23927985597

Committed 02 Apr 2026 07:45PM UTC coverage: 72.362% (+0.02%) from 72.343%

Build # 23927985597

Build Type

push

github

Committed by

daandemeyer

Commit Message

ci: Drop base64 encoding in claude review workflow

Doesn't seem to work nearly as good as the previous solution which
just told claude not to escape stuff.

Coverage Stats

319121 of 441004 relevant lines covered (72.36%)

1167673.48 hits per line

Source File
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41.99

/src/basic/terminal-util.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <fcntl.h>
#include <linux/kd.h>
#include <linux/magic.h>
#include <linux/tiocl.h>
#include <linux/vt.h>
#include <poll.h>
#include <signal.h>
#include <stdlib.h>
#include <sys/inotify.h>
#include <sys/ioctl.h>
#include <sys/sysmacros.h>
#include <termios.h>
#include <time.h>
#include <unistd.h>

#include "alloc-util.h"
#include "ansi-color.h"
#include "chase.h"
#include "devnum-util.h"
#include "errno-util.h"
#include "extract-word.h"
#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
#include "hexdecoct.h"
#include "inotify-util.h"
#include "io-util.h"
#include "log.h"
#include "namespace-util.h"
#include "parse-util.h"
#include "path-util.h"
#include "pidref.h"
#include "proc-cmdline.h"
#include "process-util.h"
#include "signal-util.h"
#include "socket-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "string-util.h"
#include "strv.h"
#include "terminal-util.h"
#include "time-util.h"
#include "utf8.h"

/* How much to wait when reading/writing ANSI sequences from/to the console */
#define CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC (333 * USEC_PER_MSEC)

static volatile unsigned cached_columns = 0;
static volatile unsigned cached_lines = 0;

static volatile int cached_on_tty = -1;
static volatile int cached_on_dev_null = -1;

bool isatty_safe(int fd) {
        assert(fd >= 0);

        if (isatty(fd))
                return true;

        /* Linux/glibc returns EIO for hung up TTY on isatty(). Which is wrong, the thing doesn't stop being
         * a TTY after all, just because it is temporarily hung up. Let's work around this here, until this
         * is fixed in glibc. See: https://sourceware.org/bugzilla/show_bug.cgi?id=32103 */
        if (errno == EIO)
                return true;

        /* Be resilient if we're working on stdio, since they're set up by parent process. */
        assert(errno != EBADF || IN_SET(fd, STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO));

        return false;
}

int chvt(int vt) {
        _cleanup_close_ int fd = -EBADF;

        /* Switch to the specified vt number. If the VT is specified <= 0 switch to the VT the kernel log messages go,
         * if that's configured. */

        fd = open_terminal("/dev/tty0", O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
        if (fd < 0)
                return fd;

        if (vt <= 0) {
                int tiocl[2] = {
                        TIOCL_GETKMSGREDIRECT,
                        0
                };

                if (ioctl(fd, TIOCLINUX, tiocl) < 0)
                        return -errno;

                vt = tiocl[0] <= 0 ? 1 : tiocl[0];
        }

        return RET_NERRNO(ioctl(fd, VT_ACTIVATE, vt));
}

int read_one_char(FILE *f, char *ret, usec_t t, bool echo, bool *need_nl) {
        _cleanup_free_ char *line = NULL;
        struct termios old_termios;
        int r, fd;

        assert(ret);

        if (!f)
                f = stdin;

        /* If this is a terminal, then switch canonical mode off, so that we can read a single
         * character. (Note that fmemopen() streams do not have an fd associated with them, let's handle that
         * nicely.) If 'echo' is false we'll also disable ECHO mode so that the pressed key is not made
         * visible to the user. */
        fd = fileno(f);
        if (fd >= 0 && tcgetattr(fd, &old_termios) >= 0) {
                struct termios new_termios = old_termios;

                new_termios.c_lflag &= ~(ICANON|(echo ? 0 : ECHO));
                new_termios.c_cc[VMIN] = 1;
                new_termios.c_cc[VTIME] = 0;

                if (tcsetattr(fd, TCSANOW, &new_termios) >= 0) {
                        char c;

                        if (t != USEC_INFINITY) {
                                if (fd_wait_for_event(fd, POLLIN, t) <= 0) {
                                        (void) tcsetattr(fd, TCSANOW, &old_termios);
                                        return -ETIMEDOUT;
                                }
                        }

                        r = safe_fgetc(f, &c);
                        (void) tcsetattr(fd, TCSANOW, &old_termios);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -EIO;

                        if (need_nl)
                                *need_nl = c != '\n';

                        *ret = c;
                        return 0;
                }
        }

        if (t != USEC_INFINITY && fd >= 0) {
                /* Let's wait the specified amount of time for input. When we have no fd we skip this, under
                 * the assumption that this is an fmemopen() stream or so where waiting doesn't make sense
                 * anyway, as the data is either already in the stream or cannot possible be placed there
                 * while we access the stream */

                if (fd_wait_for_event(fd, POLLIN, t) <= 0)
                        return -ETIMEDOUT;
        }

        /* If this is not a terminal, then read a full line instead */

        r = read_line(f, 16, &line); /* longer than necessary, to eat up UTF-8 chars/vt100 key sequences */
        if (r < 0)
                return r;
        if (r == 0)
                return -EIO;

        if (strlen(line) != 1)
                return -EBADMSG;

        if (need_nl)
                *need_nl = false;

        *ret = line[0];
        return 0;
}

#define DEFAULT_ASK_REFRESH_USEC (2*USEC_PER_SEC)

int ask_char(char *ret, const char *replies, const char *fmt, ...) {
        int r;

        assert(ret);
        assert(replies);
        assert(fmt);

        for (;;) {
                va_list ap;
                char c;
                bool need_nl = true;

                fputs(ansi_highlight(), stdout);

                putchar('\r');

                va_start(ap, fmt);
                vprintf(fmt, ap);
                va_end(ap);

                fputs(ansi_normal(), stdout);

                fflush(stdout);

                r = read_one_char(stdin, &c, DEFAULT_ASK_REFRESH_USEC, /* echo= */ true, &need_nl);
                if (r < 0) {

                        if (r == -ETIMEDOUT)
                                continue;

                        if (r == -EBADMSG) {
                                puts("Bad input, please try again.");
                                continue;
                        }

                        putchar('\n');
                        return r;
                }

                if (need_nl)
                        putchar('\n');

                if (strchr(replies, c)) {
                        *ret = c;
                        return 0;
                }

                puts("Read unexpected character, please try again.");
        }
}

typedef enum CompletionResult{
        COMPLETION_ALREADY,       /* the input string is already complete */
        COMPLETION_FULL,          /* completed the input string to be complete now */
        COMPLETION_PARTIAL,       /* completed the input string so that is still incomplete */
        COMPLETION_NONE,          /* found no matching completion */
        _COMPLETION_RESULT_MAX,
        _COMPLETION_RESULT_INVALID = -EINVAL,
        _COMPLETION_RESULT_ERRNO_MAX = -ERRNO_MAX,
} CompletionResult;

static CompletionResult pick_completion(const char *string, char *const*completions, char **ret) {
        _cleanup_free_ char *found = NULL;
        bool partial = false;

        string = strempty(string);

        STRV_FOREACH(c, completions) {

                /* Ignore entries that are not actually completions */
                if (!startswith(*c, string))
                        continue;

                /* Store first completion that matches */
                if (!found) {
                        found = strdup(*c);
                        if (!found)
                                return -ENOMEM;

                        continue;
                }

                /* If there's another completion that works truncate the one we already found by common
                 * prefix */
                size_t n = str_common_prefix(found, *c);
                if (n == SIZE_MAX)
                        continue;

                found[n] = 0;
                partial = true;
        }

        *ret = TAKE_PTR(found);

        if (!*ret)
                return COMPLETION_NONE;
        if (partial)
                return COMPLETION_PARTIAL;

        return streq(string, *ret) ? COMPLETION_ALREADY : COMPLETION_FULL;
}

static void clear_by_backspace(size_t n) {
        /* Erase the specified number of character cells backwards on the terminal */
        for (size_t i = 0; i < n; i++)
                fputs("\b \b", stdout);
}

int ask_string_full(
                char **ret,
                GetCompletionsCallback get_completions,
                void *userdata,
                const char *text, ...) {

        va_list ap;
        int r;

        assert(ret);
        assert(text);

        /* Output the prompt */
        fputs(ansi_highlight(), stdout);
        va_start(ap, text);
        vprintf(text, ap);
        va_end(ap);
        fputs(ansi_normal(), stdout);
        fflush(stdout);

        _cleanup_free_ char *string = NULL;
        size_t n = 0;

        /* Do interactive logic only if stdin + stdout are connected to the same place. And yes, we could use
         * STDIN_FILENO and STDOUT_FILENO here, but let's be overly correct for once, after all libc allows
         * swapping out stdin/stdout. */
        int fd_input = fileno(stdin);
        int fd_output = fileno(stdout);
        struct termios old_termios = TERMIOS_NULL;
        CLEANUP_TERMIOS_RESET(fd_input, old_termios);

        if (fd_input < 0 || fd_output < 0 || same_fd(fd_input, fd_output) <= 0)
                goto fallback;

        /* Try to disable echo, which also tells us if this even is a terminal */
        if (tcgetattr(fd_input, &old_termios) < 0) {
                old_termios = TERMIOS_NULL;
                goto fallback;
        }

        struct termios new_termios = old_termios;
        termios_disable_echo(&new_termios);
        if (tcsetattr(fd_input, TCSANOW, &new_termios) < 0)
                return -errno;

        for (;;) {
                int c = fgetc(stdin);

                /* On EOF or NUL, end the request, don't output anything anymore */
                if (IN_SET(c, EOF, 0))
                        break;

                /* On Return also end the request, but make this visible */
                if (IN_SET(c, '\n', '\r')) {
                        fputc('\n', stdout);
                        break;
                }

                if (c == '\t') {
                        /* Tab */

                        _cleanup_strv_free_ char **completions = NULL;
                        if (get_completions) {
                                r = get_completions(string, &completions, userdata);
                                if (r < 0)
                                        return r;
                        }

                        _cleanup_free_ char *new_string = NULL;
                        CompletionResult cr = pick_completion(string, completions, &new_string);
                        if (cr < 0)
                                return cr;
                        if (IN_SET(cr, COMPLETION_PARTIAL, COMPLETION_FULL)) {
                                /* Output the new suffix we learned */
                                fputs(ASSERT_PTR(startswith(new_string, strempty(string))), stdout);

                                /* And update the whole string */
                                free_and_replace(string, new_string);
                                n = strlen(string);
                        }
                        if (cr == COMPLETION_NONE)
                                fputc('\a', stdout); /* BEL */

                        if (IN_SET(cr, COMPLETION_PARTIAL, COMPLETION_ALREADY)) {
                                /* If this worked only partially, or if the user hit TAB even though we were
                                 * complete already, then show the remaining options (in the latter case just
                                 * the one). */
                                fputc('\n', stdout);

                                _cleanup_strv_free_ char **filtered = strv_filter_prefix(completions, string);
                                if (!filtered)
                                        return -ENOMEM;

                                r = show_menu(filtered,
                                              /* n_columns= */ SIZE_MAX,
                                              /* column_width= */ SIZE_MAX,
                                              /* ellipsize_percentage= */ 0,
                                              /* grey_prefix= */ string,
                                              /* with_numbers= */ false);
                                if (r < 0)
                                        return r;

                                /* Show the prompt again */
                                fputs(ansi_highlight(), stdout);
                                va_start(ap, text);
                                vprintf(text, ap);
                                va_end(ap);
                                fputs(ansi_normal(), stdout);
                                fputs(string, stdout);
                        }

                } else if (IN_SET(c, '\b', 127)) {
                        /* Backspace */

                        if (n == 0)
                                fputc('\a', stdout); /* BEL */
                        else {
                                size_t m = utf8_last_length(string, n);

                                char *e = string + n - m;
                                clear_by_backspace(utf8_console_width(e));

                                *e = 0;
                                n -= m;
                        }

                } else if (c == 21) {
                        /* Ctrl-u → erase all input */

                        clear_by_backspace(utf8_console_width(string));
                        if (string)
                                string[n = 0] = 0;
                        else
                                assert(n == 0);

                } else if (c == 4) {
                        /* Ctrl-d → cancel this field input */

                        return -ECANCELED;

                } else if (char_is_cc(c) || n >= LINE_MAX)
                        /* refuse control characters and too long strings */
                        fputc('\a', stdout); /* BEL */
                else {
                        /* Regular char */

                        if (!GREEDY_REALLOC(string, n+2))
                                return -ENOMEM;

                        string[n++] = (char) c;
                        string[n] = 0;

                        fputc(c, stdout);
                }

                fflush(stdout);
        }

        if (!string) {
                string = strdup("");
                if (!string)
                        return -ENOMEM;
        }

        *ret = TAKE_PTR(string);
        return 0;

fallback:
        /* A simple fallback without TTY magic */
        r = read_line(stdin, LONG_LINE_MAX, &string);
        if (r < 0)
                return r;
        if (r == 0)
                return -EIO;

        *ret = TAKE_PTR(string);
        return 0;
}

bool any_key_to_proceed(void) {

        /* Insert a new line here as well as to when the user inputs, as this is also used during the boot up
         * sequence when status messages may be interleaved with the current program output. This ensures
         * that the status messages aren't appended on the same line as this message. */

        fputc('\n', stdout);
        fputs(ansi_highlight_magenta(), stdout);
        fputs("-- Press any key to proceed --", stdout);
        fputs(ansi_normal(), stdout);
        fputc('\n', stdout);
        fflush(stdout);

        char key = 0;
        (void) read_one_char(stdin, &key, USEC_INFINITY, /* echo= */ false, /* need_nl= */ NULL);

        fputc('\n', stdout);
        fflush(stdout);

        return key != 'q';
}

static size_t widest_list_element(char *const*l) {
        size_t w = 0;

        /* Returns the largest console width of all elements in 'l' */

        STRV_FOREACH(i, l)
                w = MAX(w, utf8_console_width(*i));

        return w;
}

int show_menu(char **x,
              size_t n_columns,
              size_t column_width,
              unsigned ellipsize_percentage,
              const char *grey_prefix,
              bool with_numbers) {

        assert(n_columns > 0);

        if (n_columns == SIZE_MAX)
                n_columns = 3;

        if (column_width == SIZE_MAX) {
                size_t widest = widest_list_element(x);

                /* If not specified, derive column width from screen width */
                size_t column_max = (columns()-1) / n_columns;

                /* Subtract room for numbers */
                if (with_numbers && column_max > 6)
                        column_max -= 6;

                /* If columns would get too tight let's make this a linear list instead. */
                if (column_max < 10 && widest > 10) {
                        n_columns = 1;
                        column_max = columns()-1;

                        if (with_numbers && column_max > 6)
                                column_max -= 6;
                }

                column_width = CLAMP(widest+1, 10U, column_max);
        }

        size_t n = strv_length(x);
        size_t per_column = DIV_ROUND_UP(n, n_columns);

        size_t break_lines = lines();
        if (break_lines > 2)
                break_lines--;

        /* The first page gets two extra lines, since we want to show
         * a title */
        size_t break_modulo = break_lines;
        if (break_modulo > 3)
                break_modulo -= 3;

        for (size_t i = 0; i < per_column; i++) {

                for (size_t j = 0; j < n_columns; j++) {
                        _cleanup_free_ char *e = NULL;

                        if (j * per_column + i >= n)
                                break;

                        e = ellipsize(x[j * per_column + i], column_width, ellipsize_percentage);
                        if (!e)
                                return -ENOMEM;

                        if (with_numbers)
                                printf("%s%4zu)%s ",
                                       ansi_grey(),
                                       j * per_column + i + 1,
                                       ansi_normal());

                        if (grey_prefix && startswith(e, grey_prefix)) {
                                size_t k = MIN(strlen(grey_prefix), column_width);
                                printf("%s%.*s%s",
                                       ansi_grey(),
                                       (int) k, e,
                                       ansi_normal());
                                printf("%-*s",
                                       (int) (column_width - k), e+k);
                        } else
                                printf("%-*s", (int) column_width, e);
                }

                putchar('\n');

                /* on the first screen we reserve 2 extra lines for the title */
                if (i % break_lines == break_modulo)
                        if (!any_key_to_proceed())
                                return 0;
        }

        return 0;
}

int open_terminal(const char *name, int mode) {
        _cleanup_close_ int fd = -EBADF;

        /*
         * If a TTY is in the process of being closed opening it might cause EIO. This is horribly awful, but
         * unlikely to be changed in the kernel. Hence we work around this problem by retrying a couple of
         * times.
         *
         * https://bugs.launchpad.net/ubuntu/+source/linux/+bug/554172/comments/245
         */

        assert((mode & (O_CREAT|O_PATH|O_DIRECTORY|O_TMPFILE)) == 0);

        for (unsigned c = 0;; c++) {
                fd = open(name, mode, 0);
                if (fd >= 0)
                        break;

                if (errno != EIO)
                        return -errno;

                /* Max 1s in total */
                if (c >= 20)
                        return -EIO;

                (void) usleep_safe(50 * USEC_PER_MSEC);
        }

        if (!isatty_safe(fd))
                return -ENOTTY;

        return TAKE_FD(fd);
}

int acquire_terminal(
                const char *name,
                AcquireTerminalFlags flags,
                usec_t timeout) {

        _cleanup_close_ int notify = -EBADF, fd = -EBADF;
        usec_t ts = USEC_INFINITY;
        int r, wd = -1;

        assert(name);

        AcquireTerminalFlags mode = flags & _ACQUIRE_TERMINAL_MODE_MASK;
        assert(IN_SET(mode, ACQUIRE_TERMINAL_TRY, ACQUIRE_TERMINAL_FORCE, ACQUIRE_TERMINAL_WAIT));
        assert(mode == ACQUIRE_TERMINAL_WAIT || !FLAGS_SET(flags, ACQUIRE_TERMINAL_WATCH_SIGTERM));

        /* We use inotify to be notified when the tty is closed. We create the watch before checking if we can actually
         * acquire it, so that we don't lose any event.
         *
         * Note: strictly speaking this actually watches for the device being closed, it does *not* really watch
         * whether a tty loses its controlling process. However, unless some rogue process uses TIOCNOTTY on /dev/tty
         * *after* closing its tty otherwise this will not become a problem. As long as the administrator makes sure to
         * not configure any service on the same tty as an untrusted user this should not be a problem. (Which they
         * probably should not do anyway.) */

        if (mode == ACQUIRE_TERMINAL_WAIT) {
                notify = inotify_init1(IN_CLOEXEC | IN_NONBLOCK);
                if (notify < 0)
                        return -errno;

                wd = inotify_add_watch(notify, name, IN_CLOSE);
                if (wd < 0)
                        return -errno;

                if (timeout != USEC_INFINITY)
                        ts = now(CLOCK_MONOTONIC);
        }

        /* If we are called with ACQUIRE_TERMINAL_WATCH_SIGTERM we'll unblock SIGTERM during ppoll() temporarily */
        sigset_t poll_ss;
        assert_se(sigprocmask(SIG_SETMASK, /* newset= */ NULL, &poll_ss) >= 0);
        if (flags & ACQUIRE_TERMINAL_WATCH_SIGTERM) {
                assert_se(sigismember(&poll_ss, SIGTERM) > 0);
                assert_se(sigdelset(&poll_ss, SIGTERM) >= 0);
        }

        for (;;) {
                if (notify >= 0) {
                        r = flush_fd(notify);
                        if (r < 0)
                                return r;
                }

                /* We pass here O_NOCTTY only so that we can check the return value TIOCSCTTY and have a reliable way
                 * to figure out if we successfully became the controlling process of the tty */
                fd = open_terminal(name, O_RDWR|O_NOCTTY|O_CLOEXEC);
                if (fd < 0)
                        return fd;

                /* Temporarily ignore SIGHUP, so that we don't get SIGHUP'ed if we already own the tty. */
                struct sigaction sa_old;
                assert_se(sigaction(SIGHUP, &sigaction_ignore, &sa_old) >= 0);

                /* First, try to get the tty */
                r = RET_NERRNO(ioctl(fd, TIOCSCTTY, mode == ACQUIRE_TERMINAL_FORCE));

                /* Reset signal handler to old value */
                assert_se(sigaction(SIGHUP, &sa_old, NULL) >= 0);

                /* Success? Exit the loop now! */
                if (r >= 0)
                        break;

                /* Any failure besides -EPERM? Fail, regardless of the mode. */
                if (r != -EPERM)
                        return r;

                if (flags & ACQUIRE_TERMINAL_PERMISSIVE) /* If we are in permissive mode, then EPERM is fine, turn this
                                                          * into a success. Note that EPERM is also returned if we
                                                          * already are the owner of the TTY. */
                        break;

                if (mode != ACQUIRE_TERMINAL_WAIT) /* If we are in TRY or FORCE mode, then propagate EPERM as EPERM */
                        return r;

                assert(notify >= 0);
                assert(wd >= 0);

                for (;;) {
                        usec_t left;
                        if (timeout == USEC_INFINITY)
                                left = USEC_INFINITY;
                        else {
                                assert(ts != USEC_INFINITY);

                                usec_t n = usec_sub_unsigned(now(CLOCK_MONOTONIC), ts);
                                if (n >= timeout)
                                        return -ETIMEDOUT;

                                left = timeout - n;
                        }

                        r = ppoll_usec_full(
                                        &(struct pollfd) {
                                                .fd = notify,
                                                .events = POLLIN,
                                        },
                                        /* n_fds= */ 1,
                                        left,
                                        &poll_ss);
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -ETIMEDOUT;

                        union inotify_event_buffer buffer;
                        ssize_t l;
                        l = read(notify, &buffer, sizeof(buffer));
                        if (l < 0) {
                                if (ERRNO_IS_TRANSIENT(errno))
                                        continue;

                                return -errno;
                        }

                        FOREACH_INOTIFY_EVENT(e, buffer, l) {
                                if (e->mask & IN_Q_OVERFLOW) /* If we hit an inotify queue overflow, simply check if the terminal is up for grabs now. */
                                        break;

                                if (e->wd != wd || !(e->mask & IN_CLOSE)) /* Safety checks */
                                        return -EIO;
                        }

                        break;
                }

                /* We close the tty fd here since if the old session ended our handle will be dead. It's important that
                 * we do this after sleeping, so that we don't enter an endless loop. */
                fd = safe_close(fd);
        }

        return TAKE_FD(fd);
}

int release_terminal(void) {
        _cleanup_close_ int fd = -EBADF;
        int r;

        fd = open("/dev/tty", O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
        if (fd < 0)
                return -errno;

        /* Temporarily ignore SIGHUP, so that we don't get SIGHUP'ed
         * by our own TIOCNOTTY */
        struct sigaction sa_old;
        assert_se(sigaction(SIGHUP, &sigaction_ignore, &sa_old) >= 0);

        r = RET_NERRNO(ioctl(fd, TIOCNOTTY));

        assert_se(sigaction(SIGHUP, &sa_old, NULL) >= 0);

        return r;
}

int terminal_new_session(void) {

        /* Make us the new session leader, and set stdin tty to be our controlling terminal.
         *
         * Why stdin? Well, the ctty logic is relevant for signal delivery mostly, i.e. if people hit C-c
         * or the line is hung up. Such events are basically just a form of input, via a side channel
         * (that side channel being signal delivery, i.e. SIGINT, SIGHUP et al). Hence we focus on input,
         * not output here. */

        if (!isatty_safe(STDIN_FILENO))
                return -ENXIO;

        (void) setsid();
        return RET_NERRNO(ioctl(STDIN_FILENO, TIOCSCTTY, 0));
}

void terminal_detach_session(void) {
        (void) setsid();
        (void) release_terminal();
}

int terminal_vhangup_fd(int fd) {
        assert(fd >= 0);
        return RET_NERRNO(ioctl(fd, TIOCVHANGUP));
}

int terminal_vhangup(const char *tty) {
        _cleanup_close_ int fd = -EBADF;

        assert(tty);

        fd = open_terminal(tty, O_RDWR|O_NOCTTY|O_CLOEXEC);
        if (fd < 0)
                return fd;

        return terminal_vhangup_fd(fd);
}

int vt_disallocate(const char *tty_path) {
        assert(tty_path);

        /* Deallocate the VT if possible. If not possible (i.e. because it is the active one), at least clear
         * it entirely (including the scrollback buffer). */

        int ttynr = vtnr_from_tty(tty_path);
        if (ttynr > 0) {
                _cleanup_close_ int fd = open_terminal("/dev/tty0", O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
                if (fd < 0)
                        return fd;

                /* Try to deallocate */
                if (ioctl(fd, VT_DISALLOCATE, ttynr) >= 0)
                        return 0;
                if (errno != EBUSY)
                        return -errno;
        }

        /* So this is not a VT (in which case we cannot deallocate it), or we failed to deallocate. Let's at
         * least clear the screen. */

        _cleanup_close_ int fd2 = open_terminal(tty_path, O_WRONLY|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
        if (fd2 < 0)
                return fd2;

        return loop_write_full(fd2,
                               "\033[r"   /* clear scrolling region */
                               "\033[H"   /* move home */
                               "\033[3J"  /* clear screen including scrollback, requires Linux 2.6.40 */
                               "\033c",   /* reset to initial state */
                               SIZE_MAX,
                               CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
}

static int vt_default_utf8(void) {
        _cleanup_free_ char *b = NULL;
        int r;

        /* Read the default VT UTF8 setting from the kernel */

        r = read_one_line_file("/sys/module/vt/parameters/default_utf8", &b);
        if (r < 0)
                return r;

        return parse_boolean(b);
}

static int vt_reset_keyboard(int fd) {
        int r, kb;

        assert(fd >= 0);

        /* If we can't read the default, then default to Unicode. It's 2024 after all. */
        r = vt_default_utf8();
        if (r < 0)
                log_debug_errno(r, "Failed to determine kernel VT UTF-8 mode, assuming enabled: %m");

        kb = vt_default_utf8() != 0 ? K_UNICODE : K_XLATE;
        return RET_NERRNO(ioctl(fd, KDSKBMODE, kb));
}

static int terminal_reset_ioctl(int fd, bool switch_to_text) {
        struct termios termios;
        int r;

        /* Set terminal to some sane defaults */

        assert(fd >= 0);

        /* We leave locked terminal attributes untouched, so that Plymouth may set whatever it wants to set,
         * and we don't interfere with that. */

        /* Disable exclusive mode, just in case */
        if (ioctl(fd, TIOCNXCL) < 0)
                log_debug_errno(errno, "TIOCNXCL ioctl failed on TTY, ignoring: %m");

        /* Switch to text mode */
        if (switch_to_text)
                if (ioctl(fd, KDSETMODE, KD_TEXT) < 0)
                        log_debug_errno(errno, "KDSETMODE ioctl for switching to text mode failed on TTY, ignoring: %m");

        /* Set default keyboard mode */
        r = vt_reset_keyboard(fd);
        if (r < 0)
                log_debug_errno(r, "Failed to reset VT keyboard, ignoring: %m");

        if (tcgetattr(fd, &termios) < 0) {
                r = log_debug_errno(errno, "Failed to get terminal parameters: %m");
                goto finish;
        }

        /* We only reset the stuff that matters to the software. How
         * hardware is set up we don't touch assuming that somebody
         * else will do that for us */

        termios.c_iflag &= ~(IGNBRK | BRKINT | ISTRIP | INLCR | IGNCR | IUCLC);
        termios.c_iflag |= ICRNL | IMAXBEL | IUTF8;
        termios.c_oflag |= ONLCR | OPOST;
        termios.c_cflag |= CREAD;
        termios.c_lflag = ISIG | ICANON | IEXTEN | ECHO | ECHOE | ECHOK | ECHOCTL | ECHOKE;

        termios.c_cc[VINTR]    =   03;  /* ^C */
        termios.c_cc[VQUIT]    =  034;  /* ^\ */
        termios.c_cc[VERASE]   = 0177;
        termios.c_cc[VKILL]    =  025;  /* ^X */
        termios.c_cc[VEOF]     =   04;  /* ^D */
        termios.c_cc[VSTART]   =  021;  /* ^Q */
        termios.c_cc[VSTOP]    =  023;  /* ^S */
        termios.c_cc[VSUSP]    =  032;  /* ^Z */
        termios.c_cc[VLNEXT]   =  026;  /* ^V */
        termios.c_cc[VWERASE]  =  027;  /* ^W */
        termios.c_cc[VREPRINT] =  022;  /* ^R */
        termios.c_cc[VEOL]     =    0;
        termios.c_cc[VEOL2]    =    0;

        termios.c_cc[VTIME]  = 0;
        termios.c_cc[VMIN]   = 1;

        r = RET_NERRNO(tcsetattr(fd, TCSANOW, &termios));
        if (r < 0)
                log_debug_errno(r, "Failed to set terminal parameters: %m");

finish:
        /* Just in case, flush all crap out */
        (void) tcflush(fd, TCIOFLUSH);

        return r;
}

int terminal_reset_ansi_seq(int fd) {
        _cleanup_(nonblock_resetp) int nonblock_reset = -EBADF;
        int r;

        assert(fd >= 0);

        if (getenv_terminal_is_dumb())
                return 0;

        r = fd_nonblock(fd, true);
        if (r < 0)
                return log_debug_errno(r, "Failed to set terminal to non-blocking mode: %m");
        if (r > 0)
                nonblock_reset = fd;

        r = loop_write_full(fd,
                            "\033[!p"              /* soft terminal reset */
                            ANSI_OSC "104" ANSI_ST /* reset color palette via OSC 104 */
                            ANSI_NORMAL            /* reset colors */
                            "\033[?7h"             /* enable line-wrapping */
                            "\033[1G"              /* place cursor at beginning of current line */
                            "\033[0J",             /* erase till end of screen */
                            SIZE_MAX,
                            CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        if (r < 0)
                log_debug_errno(r, "Failed to reset terminal through ANSI sequences: %m");

        return r;
}

void reset_dev_console_fd(int fd, bool switch_to_text) {
        int r;

        assert(fd >= 0);

        _cleanup_close_ int lock_fd = lock_dev_console();
        if (lock_fd < 0)
                log_debug_errno(lock_fd, "Failed to lock /dev/console, ignoring: %m");

        r = terminal_reset_ioctl(fd, switch_to_text);
        if (r < 0)
                log_warning_errno(r, "Failed to reset /dev/console, ignoring: %m");

        unsigned rows, cols;
        r = proc_cmdline_tty_size("/dev/console", &rows, &cols);
        if (r < 0)
                log_warning_errno(r, "Failed to get /dev/console size, ignoring: %m");
        else if (r > 0) {
                r = terminal_set_size_fd(fd, NULL, rows, cols);
                if (r < 0)
                        log_warning_errno(r, "Failed to set configured terminal size on /dev/console, ignoring: %m");
        } else
                (void) terminal_fix_size(fd, fd);

        r = terminal_reset_ansi_seq(fd);
        if (r < 0)
                log_warning_errno(r, "Failed to reset /dev/console using ANSI sequences, ignoring: %m");
}

int lock_dev_console(void) {
        _cleanup_close_ int fd = -EBADF;
        int r;

        /* NB: We do not use O_NOFOLLOW here, because some container managers might place a symlink to some
         * pty in /dev/console, in which case it should be fine to lock the target TTY. */
        fd = open_terminal("/dev/console", O_RDONLY|O_CLOEXEC|O_NOCTTY);
        if (fd < 0)
                return fd;

        r = lock_generic(fd, LOCK_BSD, LOCK_EX);
        if (r < 0)
                return r;

        return TAKE_FD(fd);
}

int make_console_stdio(void) {
        int fd, r;

        /* Make /dev/console the controlling terminal and stdin/stdout/stderr, if we can. If we can't use
         * /dev/null instead. This is particularly useful if /dev/console is turned off, e.g. if console=null
         * is specified on the kernel command line. */

        fd = acquire_terminal("/dev/console", ACQUIRE_TERMINAL_FORCE|ACQUIRE_TERMINAL_PERMISSIVE, USEC_INFINITY);
        if (fd < 0) {
                log_warning_errno(fd, "Failed to acquire terminal, using /dev/null stdin/stdout/stderr instead: %m");

                r = make_null_stdio();
                if (r < 0)
                        return log_error_errno(r, "Failed to make /dev/null stdin/stdout/stderr: %m");

        } else {
                reset_dev_console_fd(fd, /* switch_to_text= */ true);

                r = rearrange_stdio(fd, fd, fd); /* This invalidates 'fd' both on success and on failure. */
                if (r < 0)
                        return log_error_errno(r, "Failed to make terminal stdin/stdout/stderr: %m");
        }

        reset_terminal_feature_caches();
        return 0;
}

static int vtnr_from_tty_raw(const char *tty, unsigned *ret) {
        assert(tty);

        tty = skip_dev_prefix(tty);

        const char *e = startswith(tty, "tty");
        if (!e)
                return -EINVAL;

        return safe_atou(e, ret);
}

int vtnr_from_tty(const char *tty) {
        unsigned u;
        int r;

        assert(tty);

        r = vtnr_from_tty_raw(tty, &u);
        if (r < 0)
                return r;
        if (!vtnr_is_valid(u))
                return -ERANGE;

        return (int) u;
}

bool tty_is_vc(const char *tty) {
        assert(tty);

        /* NB: for >= 0 values no range check is conducted here, on the assumption that the caller will
         * either extract vtnr through vtnr_from_tty() later where ERANGE would be reported, or doesn't care
         * about whether it's strictly valid, but only asking "does this fall into the vt category?", for which
         * "yes" seems to be a better answer. */

        return vtnr_from_tty_raw(tty, /* ret= */ NULL) >= 0;
}

bool tty_is_console(const char *tty) {
        assert(tty);

        return streq(skip_dev_prefix(tty), "console");
}

int resolve_dev_console(char **ret) {
        int r;

        assert(ret);

        /* Resolve where /dev/console is pointing to. If /dev/console is a symlink (like in container
         * managers), we'll just resolve the symlink. If it's a real device node, we'll use if
         * /sys/class/tty/tty0/active, but only if /sys/ is actually ours (i.e. not read-only-mounted which
         * is a sign for container setups). */

        _cleanup_free_ char *chased = NULL;
        r = chase("/dev/console", /* root= */ NULL, /* flags= */ 0, &chased, /* ret_fd= */ NULL);
        if (r < 0)
                return r;
        if (!path_equal(chased, "/dev/console")) {
                *ret = TAKE_PTR(chased);
                return 0;
        }

        r = path_is_read_only_fs("/sys");
        if (r < 0)
                return r;
        if (r > 0)
                return -ENOMEDIUM;

        _cleanup_free_ char *active = NULL;
        r = read_one_line_file("/sys/class/tty/console/active", &active);
        if (r < 0)
                return r;
        if (r == 0)
                return -ENXIO;

        /* If multiple log outputs are configured the last one is what /dev/console points to */
        const char *tty = strrchr(active, ' ');
        if (tty)
                tty++;
        else
                tty = active;

        if (streq(tty, "tty0")) {
                active = mfree(active);

                /* Get the active VC (e.g. tty1) */
                r = read_one_line_file("/sys/class/tty/tty0/active", &active);
                if (r < 0)
                        return r;
                if (r == 0)
                        return -ENXIO;

                tty = active;
        }

        _cleanup_free_ char *path = NULL;
        path = path_join("/dev", tty);
        if (!path)
                return -ENOMEM;

        *ret = TAKE_PTR(path);
        return 0;
}

int get_kernel_consoles(char ***ret) {
        _cleanup_strv_free_ char **l = NULL;
        _cleanup_free_ char *line = NULL;
        int r;

        assert(ret);

        /* If /sys/ is mounted read-only this means we are running in some kind of container environment.
         * In that case /sys/ would reflect the host system, not us, hence ignore the data we can read from it. */
        if (path_is_read_only_fs("/sys") > 0)
                goto fallback;

        r = read_one_line_file("/sys/class/tty/console/active", &line);
        if (r < 0)
                return r;

        for (const char *p = line;;) {
                _cleanup_free_ char *tty = NULL, *path = NULL;

                r = extract_first_word(&p, &tty, NULL, 0);
                if (r < 0)
                        return r;
                if (r == 0)
                        break;

                if (streq(tty, "tty0")) {
                        tty = mfree(tty);
                        r = read_one_line_file("/sys/class/tty/tty0/active", &tty);
                        if (r < 0)
                                return r;
                        if (r == 0) {
                                log_debug("No VT active, skipping /dev/tty0.");
                                continue;
                        }
                }

                path = path_join("/dev", tty);
                if (!path)
                        return -ENOMEM;

                if (access(path, F_OK) < 0) {
                        log_debug_errno(errno, "Console device %s is not accessible, skipping: %m", path);
                        continue;
                }

                r = strv_consume(&l, TAKE_PTR(path));
                if (r < 0)
                        return r;
        }

        if (strv_isempty(l)) {
                log_debug("No devices found for system console");
                goto fallback;
        }

        *ret = TAKE_PTR(l);
        return strv_length(*ret);

fallback:
        r = strv_extend(&l, "/dev/console");
        if (r < 0)
                return r;

        *ret = TAKE_PTR(l);
        return 0;
}

bool tty_is_vc_resolve(const char *tty) {
        _cleanup_free_ char *resolved = NULL;

        assert(tty);

        if (streq(skip_dev_prefix(tty), "console")) {
                if (resolve_dev_console(&resolved) < 0)
                        return false;

                tty = resolved;
        }

        return tty_is_vc(tty);
}

int fd_columns(int fd) {
        struct winsize ws = {};

        if (fd < 0)
                return -EBADF;

        if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
                return -errno;

        if (ws.ws_col <= 0)
                return -ENODATA; /* some tty types come up with invalid row/column initially, return a recognizable error for that */

        return ws.ws_col;
}

int getenv_columns(void) {
        int r;

        const char *e = getenv("COLUMNS");
        if (!e)
                return -ENXIO;

        unsigned c;
        r = safe_atou_bounded(e, 1, USHRT_MAX, &c);
        if (r < 0)
                return r;

        return (int) c;
}

unsigned columns(void) {

        if (cached_columns > 0)
                return cached_columns;

        int c = getenv_columns();
        if (c < 0) {
                c = fd_columns(STDOUT_FILENO);
                if (c < 0)
                        c = 80;
        }

        assert(c > 0);

        cached_columns = c;
        return cached_columns;
}

int fd_lines(int fd) {
        struct winsize ws = {};

        if (fd < 0)
                return -EBADF;

        if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
                return -errno;

        if (ws.ws_row <= 0)
                return -ENODATA; /* some tty types come up with invalid row/column initially, return a recognizable error for that */

        return ws.ws_row;
}

unsigned lines(void) {
        const char *e;
        int l;

        if (cached_lines > 0)
                return cached_lines;

        l = 0;
        e = getenv("LINES");
        if (e)
                (void) safe_atoi(e, &l);

        if (l <= 0 || l > USHRT_MAX) {
                l = fd_lines(STDOUT_FILENO);
                if (l <= 0)
                        l = 24;
        }

        cached_lines = l;
        return cached_lines;
}

int terminal_set_size_fd(int fd, const char *ident, unsigned rows, unsigned cols) {
        struct winsize ws;

        assert(fd >= 0);

        if (!ident)
                ident = "TTY";

        if (rows == UINT_MAX && cols == UINT_MAX)
                return 0;

        if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
                return log_debug_errno(errno,
                                       "TIOCGWINSZ ioctl for getting %s size failed, not setting terminal size: %m",
                                       ident);

        if (rows == UINT_MAX)
                rows = ws.ws_row;
        else if (rows > USHRT_MAX)
                rows = USHRT_MAX;

        if (cols == UINT_MAX)
                cols = ws.ws_col;
        else if (cols > USHRT_MAX)
                cols = USHRT_MAX;

        if (rows == ws.ws_row && cols == ws.ws_col)
                return 0;

        ws.ws_row = rows;
        ws.ws_col = cols;

        if (ioctl(fd, TIOCSWINSZ, &ws) < 0)
                return log_debug_errno(errno, "TIOCSWINSZ ioctl for setting %s size failed: %m", ident);

        return 0;
}

int proc_cmdline_tty_size(const char *tty, unsigned *ret_rows, unsigned *ret_cols) {
        _cleanup_free_ char *rowskey = NULL, *rowsvalue = NULL, *colskey = NULL, *colsvalue = NULL;
        unsigned rows = UINT_MAX, cols = UINT_MAX;
        int r;

        assert(tty);

        if (!ret_rows && !ret_cols)
                return 0;

        tty = skip_dev_prefix(tty);
        if (path_startswith(tty, "pts/"))
                return -EMEDIUMTYPE;
        if (!in_charset(tty, ALPHANUMERICAL))
                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL),
                                       "TTY name '%s' contains non-alphanumeric characters, not searching kernel cmdline for size.", tty);

        rowskey = strjoin("systemd.tty.rows.", tty);
        if (!rowskey)
                return -ENOMEM;

        colskey = strjoin("systemd.tty.columns.", tty);
        if (!colskey)
                return -ENOMEM;

        r = proc_cmdline_get_key_many(/* flags= */ 0,
                                      rowskey, &rowsvalue,
                                      colskey, &colsvalue);
        if (r < 0)
                return log_debug_errno(r, "Failed to read TTY size of %s from kernel cmdline: %m", tty);

        if (rowsvalue) {
                r = safe_atou(rowsvalue, &rows);
                if (r < 0)
                        return log_debug_errno(r, "Failed to parse %s=%s: %m", rowskey, rowsvalue);
        }

        if (colsvalue) {
                r = safe_atou(colsvalue, &cols);
                if (r < 0)
                        return log_debug_errno(r, "Failed to parse %s=%s: %m", colskey, colsvalue);
        }

        if (ret_rows)
                *ret_rows = rows;
        if (ret_cols)
                *ret_cols = cols;

        return rows != UINT_MAX || cols != UINT_MAX;
}

/* intended to be used as a SIGWINCH sighandler */
void columns_lines_cache_reset(int signum) {
        cached_columns = 0;
        cached_lines = 0;
}

void reset_terminal_feature_caches(void) {
        cached_columns = 0;
        cached_lines = 0;

        cached_on_tty = -1;
        cached_on_dev_null = -1;

        reset_ansi_feature_caches();
}

bool on_tty(void) {

        /* We check both stdout and stderr, so that situations where pipes on the shell are used are reliably
         * recognized, regardless if only the output or the errors are piped to some place. Since on_tty() is generally
         * used to default to a safer, non-interactive, non-color mode of operation it's probably good to be defensive
         * here, and check for both. Note that we don't check for STDIN_FILENO, because it should fine to use fancy
         * terminal functionality when outputting stuff, even if the input is piped to us. */

        if (cached_on_tty < 0)
                cached_on_tty =
                        isatty_safe(STDOUT_FILENO) &&
                        isatty_safe(STDERR_FILENO);

        return cached_on_tty;
}

int getttyname_malloc(int fd, char **ret) {
        char path[PATH_MAX]; /* PATH_MAX is counted *with* the trailing NUL byte */
        int r;

        assert(fd >= 0);
        assert(ret);

        r = ttyname_r(fd, path, sizeof path); /* positive error */
        assert(r >= 0);
        if (r == ERANGE)
                return -ENAMETOOLONG;
        if (r > 0)
                return -r;

        return strdup_to(ret, skip_dev_prefix(path));
}

int getttyname_harder(int fd, char **ret) {
        _cleanup_free_ char *s = NULL;
        int r;

        r = getttyname_malloc(fd, &s);
        if (r < 0)
                return r;

        if (streq(s, "tty"))
                return get_ctty(0, NULL, ret);

        *ret = TAKE_PTR(s);
        return 0;
}

int get_ctty_devnr(pid_t pid, dev_t *ret) {
        _cleanup_free_ char *line = NULL;
        unsigned long ttynr;
        const char *p;
        int r;

        assert(pid >= 0);

        p = procfs_file_alloca(pid, "stat");
        r = read_one_line_file(p, &line);
        if (r < 0)
                return r;

        p = strrchr(line, ')');
        if (!p)
                return -EIO;

        p++;

        if (sscanf(p, " "
                   "%*c "  /* state */
                   "%*d "  /* ppid */
                   "%*d "  /* pgrp */
                   "%*d "  /* session */
                   "%lu ", /* ttynr */
                   &ttynr) != 1)
                return -EIO;

        if (devnum_is_zero(ttynr))
                return -ENXIO;

        if (ret)
                *ret = (dev_t) ttynr;

        return 0;
}

int get_ctty(pid_t pid, dev_t *ret_devnr, char **ret) {
        char pty[STRLEN("/dev/pts/") + DECIMAL_STR_MAX(dev_t) + 1];
        _cleanup_free_ char *buf = NULL;
        const char *fn = NULL, *w;
        dev_t devnr;
        int r;

        r = get_ctty_devnr(pid, &devnr);
        if (r < 0)
                return r;

        r = device_path_make_canonical(S_IFCHR, devnr, &buf);
        if (r < 0) {
                struct stat st;

                if (r != -ENOENT) /* No symlink for this in /dev/char/? */
                        return r;

                /* Maybe this is PTY? PTY devices are not listed in /dev/char/, as they don't follow the
                 * Linux device model and hence device_path_make_canonical() doesn't work for them. Let's
                 * assume this is a PTY for a moment, and check if the device node this would then map to in
                 * /dev/pts/ matches the one we are looking for. This way we don't have to hardcode the major
                 * number (which is 136 btw), but we still rely on the fact that PTY numbers map directly to
                 * the minor number of the pty. */
                xsprintf(pty, "/dev/pts/%u", minor(devnr));

                if (stat(pty, &st) < 0) {
                        if (errno != ENOENT)
                                return -errno;

                } else if (S_ISCHR(st.st_mode) && devnr == st.st_rdev) /* Bingo! */
                        fn = pty;

                if (!fn) {
                        /* Doesn't exist, or not a PTY? Probably something similar to the PTYs which have no
                         * symlink in /dev/char/. Let's return something vaguely useful. */
                        r = device_path_make_major_minor(S_IFCHR, devnr, &buf);
                        if (r < 0)
                                return r;

                        fn = buf;
                }
        } else
                fn = buf;

        w = path_startswith(fn, "/dev/");
        if (!w)
                return -EINVAL;

        if (ret) {
                r = strdup_to(ret, w);
                if (r < 0)
                        return r;
        }

        if (ret_devnr)
                *ret_devnr = devnr;

        return 0;
}

int ptsname_malloc(int fd, char **ret) {
        assert(fd >= 0);
        assert(ret);

        for (size_t l = 50;;) {
                _cleanup_free_ char *c = NULL;

                c = new(char, l);
                if (!c)
                        return -ENOMEM;

                if (ptsname_r(fd, c, l) >= 0) {
                        *ret = TAKE_PTR(c);
                        return 0;
                }
                if (errno != ERANGE)
                        return -errno;

                if (!MUL_ASSIGN_SAFE(&l, 2))
                        return -ENOMEM;
        }
}

int openpt_allocate(int flags, char **ret_peer_path) {
        _cleanup_close_ int fd = -EBADF;
        int r;

        fd = posix_openpt(flags|O_NOCTTY|O_CLOEXEC);
        if (fd < 0)
                return -errno;

        _cleanup_free_ char *p = NULL;
        if (ret_peer_path) {
                r = ptsname_malloc(fd, &p);
                if (r < 0)
                        return r;

                if (!path_startswith(p, "/dev/pts/"))
                        return -EINVAL;
        }

        if (unlockpt(fd) < 0)
                return -errno;

        if (ret_peer_path)
                *ret_peer_path = TAKE_PTR(p);

        return TAKE_FD(fd);
}

static int ptsname_namespace(int pty, char **ret) {
        int no = -1;

        assert(pty >= 0);
        assert(ret);

        /* Like ptsname(), but doesn't assume that the path is
         * accessible in the local namespace. */

        if (ioctl(pty, TIOCGPTN, &no) < 0)
                return -errno;

        if (no < 0)
                return -EIO;

        if (asprintf(ret, "/dev/pts/%i", no) < 0)
                return -ENOMEM;

        return 0;
}

int openpt_allocate_in_namespace(
                const PidRef *pidref,
                int flags,
                char **ret_peer_path) {

        _cleanup_close_ int pidnsfd = -EBADF, mntnsfd = -EBADF, usernsfd = -EBADF, rootfd = -EBADF, fd = -EBADF;
        _cleanup_close_pair_ int pair[2] = EBADF_PAIR;
        int r;

        r = pidref_namespace_open(pidref, &pidnsfd, &mntnsfd, /* ret_netns_fd= */ NULL, &usernsfd, &rootfd);
        if (r < 0)
                return log_debug_errno(r, "Failed to open namespaces of PID "PID_FMT": %m", pidref->pid);

        if (socketpair(AF_UNIX, SOCK_DGRAM|SOCK_CLOEXEC, 0, pair) < 0)
                return -errno;

        r = namespace_fork(
                        "(sd-openptns)",
                        "(sd-openpt)",
                        FORK_RESET_SIGNALS|FORK_DEATHSIG_SIGKILL|FORK_WAIT,
                        pidnsfd,
                        mntnsfd,
                        /* netns_fd= */ -EBADF,
                        usernsfd,
                        rootfd,
                        /* ret= */ NULL);
        if (r < 0)
                return r;
        if (r == 0) {
                pair[0] = safe_close(pair[0]);

                fd = openpt_allocate(flags, /* ret_peer_path= */ NULL);
                if (fd < 0)
                        _exit(EXIT_FAILURE);

                if (send_one_fd(pair[1], fd, 0) < 0)
                        _exit(EXIT_FAILURE);

                _exit(EXIT_SUCCESS);
        }

        pair[1] = safe_close(pair[1]);

        fd = receive_one_fd(pair[0], 0);
        if (fd < 0)
                return fd;

        if (ret_peer_path) {
                r = ptsname_namespace(fd, ret_peer_path);
                if (r < 0)
                        return r;
        }

        return TAKE_FD(fd);
}

static bool on_dev_null(void) {
        struct stat dst, ost, est;

        if (cached_on_dev_null >= 0)
                return cached_on_dev_null;

        if (stat("/dev/null", &dst) < 0 || fstat(STDOUT_FILENO, &ost) < 0 || fstat(STDERR_FILENO, &est) < 0)
                cached_on_dev_null = false;
        else
                cached_on_dev_null = stat_inode_same(&dst, &ost) && stat_inode_same(&dst, &est);

        return cached_on_dev_null;
}

bool term_env_valid(const char *term) {
        /* Checks if the specified $TERM value is suitable for propagation, i.e. is not empty, not set to
         * "unknown" (as is common in CI), and only contains characters valid in terminal type names.
         * Valid $TERM values are things like "xterm-256color", "linux", "screen.xterm-256color", i.e.
         * alphanumeric characters, hyphens, underscores, dots, and plus signs. */
        return !isempty(term) &&
                !streq(term, "unknown") &&
                in_charset(term, ALPHANUMERICAL "-_+.");
}

bool getenv_terminal_is_dumb(void) {
        const char *e;

        e = getenv("TERM");
        if (!e)
                return true;

        return streq(e, "dumb");
}

bool terminal_is_dumb(void) {
        if (!on_tty() && !on_dev_null())
                return true;

        return getenv_terminal_is_dumb();
}

bool dev_console_colors_enabled(void) {
        _cleanup_free_ char *s = NULL;
        ColorMode m;

        /* Returns true if we assume that color is supported on /dev/console.
         *
         * For that we first check if we explicitly got told to use colors or not, by checking $SYSTEMD_COLORS. If that
         * isn't set we check whether PID 1 has $TERM set, and if not, whether TERM is set on the kernel command
         * line. If we find $TERM set we assume color if it's not set to "dumb", similarly to how regular
         * colors_enabled() operates. */

        m = parse_systemd_colors();
        if (m >= 0)
                return m;

        if (getenv("NO_COLOR"))
                return false;

        if (getenv_for_pid(1, "TERM", &s) <= 0)
                (void) proc_cmdline_get_key("TERM", 0, &s);

        return !streq_ptr(s, "dumb");
}

int vt_restore(int fd) {

        static const struct vt_mode mode = {
                .mode = VT_AUTO,
        };

        int r, ret = 0;

        assert(fd >= 0);

        if (!isatty_safe(fd))
                return log_debug_errno(SYNTHETIC_ERRNO(ENOTTY), "Asked to restore the VT for an fd that does not refer to a terminal.");

        if (ioctl(fd, KDSETMODE, KD_TEXT) < 0)
                RET_GATHER(ret, log_debug_errno(errno, "Failed to set VT to text mode, ignoring: %m"));

        r = vt_reset_keyboard(fd);
        if (r < 0)
                RET_GATHER(ret, log_debug_errno(r, "Failed to reset keyboard mode, ignoring: %m"));

        if (ioctl(fd, VT_SETMODE, &mode) < 0)
                RET_GATHER(ret, log_debug_errno(errno, "Failed to set VT_AUTO mode, ignoring: %m"));

        r = fchmod_and_chown(fd, TTY_MODE, 0, GID_INVALID);
        if (r < 0)
                RET_GATHER(ret, log_debug_errno(r, "Failed to chmod()/chown() VT, ignoring: %m"));

        return ret;
}

int vt_release(int fd, bool restore) {
        assert(fd >= 0);

        /* This function releases the VT by acknowledging the VT-switch signal
         * sent by the kernel and optionally reset the VT in text and auto
         * VT-switching modes. */

        if (!isatty_safe(fd))
                return log_debug_errno(SYNTHETIC_ERRNO(ENOTTY), "Asked to release the VT for an fd that does not refer to a terminal.");

        if (ioctl(fd, VT_RELDISP, 1) < 0)
                return -errno;

        if (restore)
                return vt_restore(fd);

        return 0;
}

void get_log_colors(int priority, const char **on, const char **off, const char **highlight) {
        /* Note that this will initialize output variables only when there's something to output.
         * The caller must pre-initialize to "" or NULL as appropriate. */

        if (priority <= LOG_ERR) {
                if (on)
                        *on = ansi_highlight_red();
                if (off)
                        *off = ansi_normal();
                if (highlight)
                        *highlight = ansi_highlight();

        } else if (priority <= LOG_WARNING) {
                if (on)
                        *on = ansi_highlight_yellow();
                if (off)
                        *off = ansi_normal();
                if (highlight)
                        *highlight = ansi_highlight();

        } else if (priority <= LOG_NOTICE) {
                if (on)
                        *on = ansi_highlight();
                if (off)
                        *off = ansi_normal();
                if (highlight)
                        *highlight = ansi_highlight_red();

        } else if (priority >= LOG_DEBUG) {
                if (on)
                        *on = ansi_grey();
                if (off)
                        *off = ansi_normal();
                if (highlight)
                        *highlight = ansi_highlight_red();
        }
}

int terminal_set_cursor_position(int fd, unsigned row, unsigned column) {
        assert(fd >= 0);

        char cursor_position[STRLEN("\x1B[" ";" "H") + DECIMAL_STR_MAX(unsigned) * 2 + 1];
        xsprintf(cursor_position, "\x1B[%u;%uH", row, column);

        return loop_write(fd, cursor_position, SIZE_MAX);
}

static int terminal_verify_same(int input_fd, int output_fd) {
        assert(input_fd >= 0);
        assert(output_fd >= 0);

        /* Validates that the specified fds reference the same TTY */

        if (input_fd != output_fd) {
                struct stat sti;
                if (fstat(input_fd, &sti) < 0)
                        return -errno;

                if (!S_ISCHR(sti.st_mode)) /* TTYs are character devices */
                        return -ENOTTY;

                struct stat sto;
                if (fstat(output_fd, &sto) < 0)
                        return -errno;

                if (!S_ISCHR(sto.st_mode))
                        return -ENOTTY;

                if (sti.st_rdev != sto.st_rdev)
                        return -ENOLINK;
        }

        if (!isatty_safe(input_fd)) /* The check above was just for char device, but now let's ensure it's actually a tty */
                return -ENOTTY;

        return 0;
}

typedef enum CursorPositionState {
        CURSOR_TEXT,
        CURSOR_ESCAPE,
        CURSOR_ROW,
        CURSOR_COLUMN,
} CursorPositionState;

typedef struct CursorPositionContext {
        CursorPositionState state;
        unsigned row, column;
} CursorPositionContext;

static int scan_cursor_position_response(
                CursorPositionContext *context,
                const char *buf,
                size_t size,
                size_t *ret_processed) {

        assert(context);
        assert(buf);
        assert(ret_processed);

        for (size_t i = 0; i < size; i++) {
                char c = buf[i];

                switch (context->state) {

                case CURSOR_TEXT:
                        context->state = c == '\x1B' ? CURSOR_ESCAPE : CURSOR_TEXT;
                        break;

                case CURSOR_ESCAPE:
                        context->state = c == '[' ? CURSOR_ROW : CURSOR_TEXT;
                        break;

                case CURSOR_ROW:
                        if (c == ';')
                                context->state = context->row > 0 ? CURSOR_COLUMN : CURSOR_TEXT;
                        else {
                                int d = undecchar(c);

                                /* We read a decimal character, let's suffix it to the number we so far read,
                                 * but let's do an overflow check first. */
                                if (d < 0 || context->row > (UINT_MAX-d)/10)
                                        context->state = CURSOR_TEXT;
                                else
                                        context->row = context->row * 10 + d;
                        }
                        break;

                case CURSOR_COLUMN:
                        if (c == 'R') {
                                if (context->column > 0) {
                                        *ret_processed = i + 1;
                                        return 1; /* success! */
                                }

                                context->state = CURSOR_TEXT;
                        } else {
                                int d = undecchar(c);

                                /* As above, add the decimal character to our column number */
                                if (d < 0 || context->column > (UINT_MAX-d)/10)
                                        context->state = CURSOR_TEXT;
                                else
                                        context->column = context->column * 10 + d;
                        }

                        break;
                }

                /* Reset any positions we might have picked up */
                if (IN_SET(context->state, CURSOR_TEXT, CURSOR_ESCAPE))
                        context->row = context->column = 0;
        }

        *ret_processed = size;
        return 0; /* all good, but not enough data yet */
}

int terminal_get_cursor_position(
                int input_fd,
                int output_fd,
                unsigned *ret_row,
                unsigned *ret_column) {

        _cleanup_close_ int nonblock_input_fd = -EBADF;
        int r;

        assert(input_fd >= 0);
        assert(output_fd >= 0);

        if (getenv_terminal_is_dumb())
                return -EOPNOTSUPP;

        r = terminal_verify_same(input_fd, output_fd);
        if (r < 0)
                return log_debug_errno(r, "Called with distinct input/output fds: %m");

        /* Failure to reset the terminal is ignored here and in similar cases below.
         * We already have our result; if cleanup fails it doesn't change the validity of the result. */
        struct termios old_termios = TERMIOS_NULL;
        CLEANUP_TERMIOS_RESET(input_fd, old_termios);

        if (tcgetattr(input_fd, &old_termios) < 0)
                return log_debug_errno(errno, "Failed to get terminal settings: %m");

        struct termios new_termios = old_termios;
        termios_disable_echo(&new_termios);

        if (tcsetattr(input_fd, TCSANOW, &new_termios) < 0)
                return log_debug_errno(errno, "Failed to set new terminal settings: %m");

        /* Request cursor position (DSR/CPR) */
        r = loop_write(output_fd, "\x1B[6n", SIZE_MAX);
        if (r < 0)
                return r;

        /* Open a 2nd input fd, in non-blocking mode, so that we won't ever hang in read() should someone
         * else process the POLLIN. */

        nonblock_input_fd = r = fd_reopen(input_fd, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
        if (r < 0)
                return r;

        usec_t end = usec_add(now(CLOCK_MONOTONIC), CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        char buf[STRLEN("\x1B[1;1R")]; /* The shortest valid reply possible */
        size_t buf_full = 0;
        CursorPositionContext context = {};

        for (bool first = true;; first = false) {
                if (buf_full == 0) {
                        usec_t n = now(CLOCK_MONOTONIC);
                        if (n >= end)
                                return -EOPNOTSUPP;

                        r = fd_wait_for_event(nonblock_input_fd, POLLIN, usec_sub_unsigned(end, n));
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -EOPNOTSUPP;

                        /* On the first try, read multiple characters, i.e. the shortest valid
                         * reply. Afterwards read byte-wise, since we don't want to read too much, and
                         * unnecessarily drop too many characters from the input queue. */
                        ssize_t l = read(nonblock_input_fd, buf, first ? sizeof(buf) : 1);
                        if (l < 0) {
                                if (errno == EAGAIN)
                                        continue;

                                return -errno;
                        }

                        assert((size_t) l <= sizeof(buf));
                        buf_full = l;
                }

                size_t processed;
                r = scan_cursor_position_response(&context, buf, buf_full, &processed);
                if (r < 0)
                        return r;

                assert(processed <= buf_full);
                buf_full -= processed;
                memmove(buf, buf + processed, buf_full);

                if (r > 0) {
                        /* Superficial validity check */
                        if (context.row >= 32766 || context.column >= 32766)
                                return -ENODATA;

                        if (ret_row)
                                *ret_row = context.row;
                        if (ret_column)
                                *ret_column = context.column;

                        return 0;
                }
        }
}

int terminal_reset_defensive(int fd, TerminalResetFlags flags) {
        int r = 0;

        assert(fd >= 0);
        assert(!FLAGS_SET(flags, TERMINAL_RESET_AVOID_ANSI_SEQ|TERMINAL_RESET_FORCE_ANSI_SEQ));

        /* Resets the terminal comprehensively, i.e. via both ioctl()s and via ANSI sequences, but do so only
         * if $TERM is unset or set to "dumb" */

        if (!isatty_safe(fd))
                return -ENOTTY;

        RET_GATHER(r, terminal_reset_ioctl(fd, FLAGS_SET(flags, TERMINAL_RESET_SWITCH_TO_TEXT)));

        if (!FLAGS_SET(flags, TERMINAL_RESET_AVOID_ANSI_SEQ) &&
            (FLAGS_SET(flags, TERMINAL_RESET_FORCE_ANSI_SEQ) || !getenv_terminal_is_dumb()))
                RET_GATHER(r, terminal_reset_ansi_seq(fd));

        return r;
}

int terminal_reset_defensive_locked(int fd, TerminalResetFlags flags) {
        assert(fd >= 0);

        _cleanup_close_ int lock_fd = lock_dev_console();
        if (lock_fd < 0)
                log_debug_errno(lock_fd, "Failed to acquire lock for /dev/console, ignoring: %m");

        return terminal_reset_defensive(fd, flags);
}

void termios_disable_echo(struct termios *termios) {
        assert(termios);

        termios->c_lflag &= ~(ICANON|ECHO);
        termios->c_cc[VMIN] = 1;
        termios->c_cc[VTIME] = 0;
}

static bool termios_is_null(const struct termios *t) {
        if (!t)
                return true;

        return t->c_iflag == UINT_MAX &&
               t->c_oflag == UINT_MAX &&
               t->c_cflag == UINT_MAX &&
               t->c_lflag == UINT_MAX;
}

void termios_reset(const TermiosResetContext *c) {
        assert(c);

        PROTECT_ERRNO;

        if (c->fd && *c->fd >= 0 && !termios_is_null(c->termios))
                (void) tcsetattr(*c->fd, TCSANOW, c->termios);
}

typedef enum BackgroundColorState {
        BACKGROUND_TEXT,
        BACKGROUND_ESCAPE,
        BACKGROUND_BRACKET,
        BACKGROUND_FIRST_ONE,
        BACKGROUND_SECOND_ONE,
        BACKGROUND_SEMICOLON,
        BACKGROUND_R,
        BACKGROUND_G,
        BACKGROUND_B,
        BACKGROUND_RED,
        BACKGROUND_GREEN,
        BACKGROUND_BLUE,
        BACKGROUND_STRING_TERMINATOR,
} BackgroundColorState;

typedef struct BackgroundColorContext {
        BackgroundColorState state;
        uint32_t red, green, blue;
        unsigned red_bits, green_bits, blue_bits;
} BackgroundColorContext;

static int scan_background_color_response(
                BackgroundColorContext *context,
                const char *buf,
                size_t size,
                size_t *ret_processed) {

        assert(context);
        assert(buf);
        assert(ret_processed);

        for (size_t i = 0; i < size; i++) {
                char c = buf[i];

                switch (context->state) {

                case BACKGROUND_TEXT:
                        context->state = c == '\x1B' ? BACKGROUND_ESCAPE : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_ESCAPE:
                        context->state = c == ']' ? BACKGROUND_BRACKET : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_BRACKET:
                        context->state = c == '1' ? BACKGROUND_FIRST_ONE : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_FIRST_ONE:
                        context->state = c == '1' ? BACKGROUND_SECOND_ONE : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_SECOND_ONE:
                        context->state = c == ';' ? BACKGROUND_SEMICOLON : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_SEMICOLON:
                        context->state = c == 'r' ? BACKGROUND_R : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_R:
                        context->state = c == 'g' ? BACKGROUND_G : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_G:
                        context->state = c == 'b' ? BACKGROUND_B : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_B:
                        context->state = c == ':' ? BACKGROUND_RED : BACKGROUND_TEXT;
                        break;

                case BACKGROUND_RED:
                        if (c == '/')
                                context->state = context->red_bits > 0 ? BACKGROUND_GREEN : BACKGROUND_TEXT;
                        else {
                                int d = unhexchar(c);
                                if (d < 0 || context->red_bits >= sizeof(context->red)*8)
                                        context->state = BACKGROUND_TEXT;
                                else {
                                        context->red = (context->red << 4) | d;
                                        context->red_bits += 4;
                                }
                        }
                        break;

                case BACKGROUND_GREEN:
                        if (c == '/')
                                context->state = context->green_bits > 0 ? BACKGROUND_BLUE : BACKGROUND_TEXT;
                        else {
                                int d = unhexchar(c);
                                if (d < 0 || context->green_bits >= sizeof(context->green)*8)
                                        context->state = BACKGROUND_TEXT;
                                else {
                                        context->green = (context->green << 4) | d;
                                        context->green_bits += 4;
                                }
                        }
                        break;

                case BACKGROUND_BLUE:
                        if (c == '\x07') {
                                if (context->blue_bits > 0) {
                                        *ret_processed = i + 1;
                                        return 1; /* success! */
                                }

                                context->state = BACKGROUND_TEXT;
                        } else if (c == '\x1b')
                                context->state = context->blue_bits > 0 ? BACKGROUND_STRING_TERMINATOR : BACKGROUND_TEXT;
                        else {
                                int d = unhexchar(c);
                                if (d < 0 || context->blue_bits >= sizeof(context->blue)*8)
                                        context->state = BACKGROUND_TEXT;
                                else {
                                        context->blue = (context->blue << 4) | d;
                                        context->blue_bits += 4;
                                }
                        }
                        break;

                case BACKGROUND_STRING_TERMINATOR:
                        if (c == '\\') {
                                *ret_processed = i + 1;
                                return 1; /* success! */
                        }

                        context->state = c == ']' ? BACKGROUND_ESCAPE : BACKGROUND_TEXT;
                        break;

                }

                /* Reset any colors we might have picked up */
                if (IN_SET(context->state, BACKGROUND_TEXT, BACKGROUND_ESCAPE)) {
                        /* reset color */
                        context->red = context->green = context->blue = 0;
                        context->red_bits = context->green_bits = context->blue_bits = 0;
                }
        }

        *ret_processed = size;
        return 0; /* all good, but not enough data yet */
}

int get_default_background_color(double *ret_red, double *ret_green, double *ret_blue) {
        int r;

        assert(ret_red);
        assert(ret_green);
        assert(ret_blue);

        if (!colors_enabled())
                return -EOPNOTSUPP;

        r = terminal_verify_same(STDIN_FILENO, STDOUT_FILENO);
        if (r < 0)
                return r;

        if (streq_ptr(getenv("TERM"), "linux")) {
                /* Linux console is black */
                *ret_red = *ret_green = *ret_blue = 0.0;
                return 0;
        }

        /* Open a 2nd input fd, in non-blocking mode, so that we won't ever hang in read()
         * should someone else process the POLLIN. Do all subsequent operations on the new fd. */
        _cleanup_close_ int nonblock_input_fd = r = fd_reopen(STDIN_FILENO, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
        if (r < 0)
                return r;

        struct termios old_termios = TERMIOS_NULL;
        CLEANUP_TERMIOS_RESET(nonblock_input_fd, old_termios);

        if (tcgetattr(nonblock_input_fd, &old_termios) < 0)
                return -errno;

        struct termios new_termios = old_termios;
        termios_disable_echo(&new_termios);

        if (tcsetattr(nonblock_input_fd, TCSANOW, &new_termios) < 0)
                return -errno;

        r = loop_write(STDOUT_FILENO, ANSI_OSC "11;?" ANSI_ST, SIZE_MAX);
        if (r < 0)
                return r;

        usec_t end = usec_add(now(CLOCK_MONOTONIC), CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        char buf[STRLEN(ANSI_OSC "11;rgb:0/0/0" ANSI_ST)]; /* shortest possible reply */
        size_t buf_full = 0;
        BackgroundColorContext context = {};

        for (bool first = true;; first = false) {
                if (buf_full == 0) {
                        usec_t n = now(CLOCK_MONOTONIC);
                        if (n >= end)
                                return -EOPNOTSUPP;

                        r = fd_wait_for_event(nonblock_input_fd, POLLIN, usec_sub_unsigned(end, n));
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -EOPNOTSUPP;

                        /* On the first try, read multiple characters, i.e. the shortest valid
                         * reply. Afterwards read byte-wise, since we don't want to read too much, and
                         * unnecessarily drop too many characters from the input queue. */
                        ssize_t l = read(nonblock_input_fd, buf, first ? sizeof(buf) : 1);
                        if (l < 0) {
                                if (errno == EAGAIN)
                                        continue;
                                return -errno;
                        }

                        assert((size_t) l <= sizeof(buf));
                        buf_full = l;
                }

                size_t processed;
                r = scan_background_color_response(&context, buf, buf_full, &processed);
                if (r < 0)
                        return r;

                assert(processed <= buf_full);
                buf_full -= processed;
                memmove(buf, buf + processed, buf_full);

                if (r > 0) {
                        assert(context.red_bits > 0);
                        *ret_red = (double) context.red / ((UINT64_C(1) << context.red_bits) - 1);
                        assert(context.green_bits > 0);
                        *ret_green = (double) context.green / ((UINT64_C(1) << context.green_bits) - 1);
                        assert(context.blue_bits > 0);
                        *ret_blue = (double) context.blue / ((UINT64_C(1) << context.blue_bits) - 1);
                        return 0;
                }
        }
}

/* Determine terminal dimensions by means of ANSI sequences: save the cursor via DECSC, position it far
 * to the bottom right (clamped to actual terminal dimensions), read back via DSR where we ended up, and
 * restore cursor via DECRC. Only needs a single DSR round-trip, and always restores the cursor regardless
 * of whether the response is received.
 *
 * Caller must have already opened a non-blocking input fd and configured termios (echo/icanon off). */
static int terminal_query_size_by_dsr(
                int nonblock_input_fd,
                int output_fd,
                unsigned *ret_rows,
                unsigned *ret_columns) {

        int r;

        assert(nonblock_input_fd >= 0);
        assert(output_fd >= 0);

        /* Use DECSC/DECRC to save/restore cursor instead of querying position via DSR. This way the cursor
         * is always restored — even on timeout — and we only need one DSR response instead of two. */
        r = loop_write_full(output_fd,
                            "\x1B" "7"              /* DECSC: save cursor position */
                            "\x1B[32766;32766H"     /* CUP: position cursor far to the right and to the bottom, staying within 16bit signed range */
                            "\x1B[6n"               /* DSR: request cursor position (CPR) */
                            "\x1B" "8",             /* DECRC: restore cursor position */
                            SIZE_MAX,
                            CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        if (r < 0)
                return r;

        usec_t end = usec_add(now(CLOCK_MONOTONIC), CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        char buf[STRLEN("\x1B[1;1R")]; /* The shortest valid reply possible */
        size_t buf_full = 0;
        CursorPositionContext context = {};

        for (bool first = true;; first = false) {
                if (buf_full == 0) {
                        usec_t n = now(CLOCK_MONOTONIC);
                        if (n >= end)
                                return -EOPNOTSUPP;

                        r = fd_wait_for_event(nonblock_input_fd, POLLIN, usec_sub_unsigned(end, n));
                        if (r < 0)
                                return r;
                        if (r == 0)
                                return -EOPNOTSUPP;

                        /* On the first try, read multiple characters, i.e. the shortest valid
                         * reply. Afterwards read byte-wise, since we don't want to read too much, and
                         * unnecessarily drop too many characters from the input queue. */
                        ssize_t l = read(nonblock_input_fd, buf, first ? sizeof(buf) : 1);
                        if (l < 0) {
                                if (errno == EAGAIN)
                                        continue;

                                return -errno;
                        }

                        assert((size_t) l <= sizeof(buf));
                        buf_full = l;
                }

                size_t processed;
                r = scan_cursor_position_response(&context, buf, buf_full, &processed);
                if (r < 0)
                        return r;

                assert(processed <= buf_full);
                buf_full -= processed;
                memmove(buf, buf + processed, buf_full);

                if (r > 0) {
                        /* Superficial validity checks (no particular reason to check for < 4, it's
                         * just a way to look for unreasonably small values) */
                        if (context.row < 4 || context.column < 4 || context.row >= 32766 || context.column >= 32766)
                                return -ENODATA;

                        if (ret_rows)
                                *ret_rows = context.row;
                        if (ret_columns)
                                *ret_columns = context.column;

                        return 0;
                }
        }
}

/* Common setup for ANSI terminal queries: validate the fds, open a non-blocking input fd, and configure
 * termios with echo and canonical mode disabled. Caller must restore termios and close the fd when done. */
static int terminal_prepare_query(
                int input_fd,
                int output_fd,
                int *ret_nonblock_fd,
                struct termios *ret_saved_termios) {

        int r;

        assert(input_fd >= 0);
        assert(output_fd >= 0);
        assert(ret_nonblock_fd);
        assert(ret_saved_termios);

        /* Use getenv_terminal_is_dumb() instead of terminal_is_dumb() here since we operate on an
         * explicitly passed fd, not on stdio. terminal_is_dumb() additionally checks on_tty() which
         * tests whether *stderr* is a tty — that's irrelevant when we're querying a directly opened
         * terminal such as /dev/console. */
        if (getenv_terminal_is_dumb())
                return -EOPNOTSUPP;

        r = terminal_verify_same(input_fd, output_fd);
        if (r < 0)
                return log_debug_errno(r, "Called with distinct input/output fds: %m");

        /* Open a 2nd input fd, in non-blocking mode, so that we won't ever hang in read()
         * should someone else process the POLLIN. Do all subsequent operations on the new fd. */
        _cleanup_close_ int nonblock_input_fd = r = fd_reopen(input_fd, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
        if (r < 0)
                return r;

        if (tcgetattr(nonblock_input_fd, ret_saved_termios) < 0)
                return log_debug_errno(errno, "Failed to get terminal settings: %m");

        struct termios new_termios = *ret_saved_termios;
        termios_disable_echo(&new_termios);

        if (tcsetattr(nonblock_input_fd, TCSANOW, &new_termios) < 0)
                return log_debug_errno(errno, "Failed to set new terminal settings: %m");

        *ret_nonblock_fd = TAKE_FD(nonblock_input_fd);
        return 0;
}

/*
 * See https://terminalguide.namepad.de/seq/csi_st-18/,
 * https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h3-Functions-using-CSI-_-ordered-by-the-final-character_s_.
 */
#define CSI18_Q  "\x1B[18t"               /* Report the size of the text area in characters */
#define CSI18_Rp "\x1B[8;"                /* Reply prefix */
#define CSI18_R0 CSI18_Rp "1;1t"          /* Shortest reply */
#define CSI18_R1 CSI18_Rp "32766;32766t"  /* Longest reply */

static int scan_text_area_size_response(
                const char *buf,
                size_t size,
                unsigned *ret_rows,
                unsigned *ret_columns) {

        assert(buf);
        assert(ret_rows);
        assert(ret_columns);

        /* Check if we have enough space for the shortest possible answer. */
        if (size < STRLEN(CSI18_R0))
                return -EAGAIN;

        /* Check if the terminating sequence is present */
        if (buf[size - 1] != 't')
                return -EAGAIN;

        unsigned short rows, columns;
        if (sscanf(buf, CSI18_Rp "%hu;%hut", &rows, &columns) != 2)
                return -EINVAL;

        *ret_rows = rows;
        *ret_columns = columns;
        return 0;
}

/* Determine terminal dimensions by means of an ANSI CSI 18 sequence.
 *
 * Caller must have already opened a non-blocking input fd and configured termios (echo/icanon off). */
static int terminal_query_size_by_csi18(
                int nonblock_input_fd,
                int output_fd,
                unsigned *ret_rows,
                unsigned *ret_columns) {

        int r;

        assert(nonblock_input_fd >= 0);
        assert(output_fd >= 0);

        r = loop_write_full(output_fd, CSI18_Q, SIZE_MAX, CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        if (r < 0)
                return r;

        usec_t end = usec_add(now(CLOCK_MONOTONIC), CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        char buf[STRLEN(CSI18_R1)];
        size_t bytes = 0;

        for (;;) {
                usec_t n = now(CLOCK_MONOTONIC);
                if (n >= end)
                        return -EOPNOTSUPP;

                r = fd_wait_for_event(nonblock_input_fd, POLLIN, usec_sub_unsigned(end, n));
                if (r < 0)
                        return r;
                if (r == 0)
                        return -EOPNOTSUPP;

                /* On the first read, read multiple characters, i.e. the shortest valid reply. Afterwards
                 * read byte by byte, since we don't want to read too much and drop characters from the input
                 * queue. */
                ssize_t l = read(nonblock_input_fd, buf + bytes, bytes == 0 ? STRLEN(CSI18_R0) : 1);
                if (l < 0) {
                        if (errno == EAGAIN)
                                continue;
                        return -errno;
                }

                assert((size_t) l <= sizeof(buf) - bytes);
                bytes += l;

                r = scan_text_area_size_response(buf, bytes, ret_rows, ret_columns);
                if (r != -EAGAIN)
                        return r;

                if (bytes == sizeof(buf))
                        return -EOPNOTSUPP; /* The response has the right prefix, but we didn't find a valid
                                             * answer with a terminator in the allotted space. Something is
                                             * wrong, possibly some unrelated bytes got injected into the
                                             * answer. */
        }
}

int terminal_get_size(
                int input_fd,
                int output_fd,
                unsigned *ret_rows,
                unsigned *ret_columns,
                bool try_dsr,
                bool try_csi18) {

        _cleanup_close_ int nonblock_input_fd = -EBADF;
        struct termios old_termios = TERMIOS_NULL;
        CLEANUP_TERMIOS_RESET(nonblock_input_fd, old_termios);
        _cleanup_(nonblock_resetp) int nonblock_reset = -EBADF;
        int r;

        assert(try_dsr || try_csi18);

        r = terminal_prepare_query(input_fd, output_fd, &nonblock_input_fd, &old_termios);
        if (r < 0)
                return r;

        /* Put the output fd in non-blocking mode with a write timeout, to avoid blocking indefinitely on
         * write if the terminal is not consuming data (e.g. serial console with flow control). */
        r = fd_nonblock(output_fd, true);
        if (r < 0)
                return log_debug_errno(r, "Failed to set terminal to non-blocking mode: %m");
        if (r > 0)
                nonblock_reset = output_fd;

        /* Flush any stale input that might confuse the response parsers. */
        (void) tcflush(nonblock_input_fd, TCIFLUSH);

        if (try_csi18) {
                r = terminal_query_size_by_csi18(nonblock_input_fd, output_fd, ret_rows, ret_columns);
                if (r >= 0)
                        return r;

                /* Query failed. Flush any outstanding input. */
                (void) tcflush(nonblock_input_fd, TCIFLUSH);

                if (!IN_SET(r, -EOPNOTSUPP, -EINVAL))
                        return r;
        }

        if (try_dsr) {
                r = terminal_query_size_by_dsr(nonblock_input_fd, output_fd, ret_rows, ret_columns);
                if (r >= 0)
                        return r;

                /* Query failed. Flush any outstanding input. */
                (void) tcflush(nonblock_input_fd, TCIFLUSH);
        }

        return r;
}

int terminal_fix_size(int input_fd, int output_fd) {
        unsigned rows, columns;
        int r;

        /* Tries to update the current terminal dimensions to the ones reported via ANSI sequences.
         *
         * Why bother with this? The ioctl() information is often incorrect on serial terminals (since
         * there's no handshake or protocol to determine the right dimensions in RS232), but since the ANSI
         * sequences are interpreted by the final terminal instead of an intermediary tty driver they should
         * be more accurate.
         */

        struct winsize ws = {};
        if (ioctl(output_fd, TIOCGWINSZ, &ws) < 0)
                return log_debug_errno(errno, "Failed to query terminal dimensions, ignoring: %m");

        r = terminal_get_size(input_fd, output_fd, &rows, &columns, /* try_dsr= */ true, /* try_csi18= */ true);
        if (r < 0)
                return log_debug_errno(r, "Failed to acquire terminal dimensions via ANSI sequences, not adjusting terminal dimensions: %m");

        if (ws.ws_row == rows && ws.ws_col == columns) {
                log_debug("Terminal dimensions reported via ANSI sequences match currently set terminal dimensions, not changing.");
                return 0;
        }

        ws.ws_col = columns;
        ws.ws_row = rows;

        if (ioctl(output_fd, TIOCSWINSZ, &ws) < 0)
                return log_debug_errno(errno, "Failed to update terminal dimensions, ignoring: %m");

        log_debug("Fixed terminal dimensions to %ux%u based on ANSI sequence information.", columns, rows);
        return 1;
}

#define MAX_TERMINFO_LENGTH 64
/* python -c 'print("".join(hex(ord(i))[2:] for i in "name").upper())' */
#define DCS_TERMINFO_Q ANSI_DCS "+q" "6E616D65" ANSI_ST
/* The answer is either 0+r… (invalid) or 1+r… (OK). */
#define DCS_TERMINFO_R0 ANSI_DCS "0+r" ANSI_ST
#define DCS_TERMINFO_R1 ANSI_DCS "1+r" "6E616D65" "=" /* This is followed by Pt ST. */
assert_cc(STRLEN(DCS_TERMINFO_R0) <= STRLEN(DCS_TERMINFO_R1 ANSI_ST));

static int scan_terminfo_response(
                const char *buf,
                size_t size,
                char **ret_name) {
        int r;

        assert(buf);
        assert(ret_name);

        /* Check if we have enough space for the shortest possible answer. */
        if (size < STRLEN(DCS_TERMINFO_R0))
                return -EAGAIN;

        /* Check if the terminating sequence is present */
        if (memcmp(buf + size - STRLEN(ANSI_ST), ANSI_ST, STRLEN(ANSI_ST)) != 0)
                return -EAGAIN;

        if (size <= STRLEN(DCS_TERMINFO_R1 ANSI_ST))
                return -EINVAL;  /* The answer is invalid or empty */

        if (memcmp(buf, DCS_TERMINFO_R1, STRLEN(DCS_TERMINFO_R1)) != 0)
                return -EINVAL;  /* The answer is not valid */

        _cleanup_free_ void *dec = NULL;
        size_t dec_size;
        r = unhexmem_full(buf + STRLEN(DCS_TERMINFO_R1), size - STRLEN(DCS_TERMINFO_R1 ANSI_ST),
                          /* secure= */ false,
                          &dec, &dec_size);
        if (r < 0)
                return r;

        assert(((const char *) dec)[dec_size] == '\0'); /* unhexmem appends NUL for our convenience */
        if (memchr(dec, '\0', dec_size) || string_has_cc(dec, NULL) || !filename_is_valid(dec))
                return -EUCLEAN;

        *ret_name = TAKE_PTR(dec);
        return 0;
}

int terminal_get_terminfo_by_dcs(int fd, char **ret_name) {
        int r;

        assert(fd >= 0);
        assert(ret_name);

        /* Note: fd must be in non-blocking read-write mode! */

        struct termios old_termios = TERMIOS_NULL;
        CLEANUP_TERMIOS_RESET(fd, old_termios);

        if (tcgetattr(fd, &old_termios) < 0)
                return -errno;

        struct termios new_termios = old_termios;
        termios_disable_echo(&new_termios);

        if (tcsetattr(fd, TCSANOW, &new_termios) < 0)
                return -errno;

        r = loop_write(fd, DCS_TERMINFO_Q, SIZE_MAX);
        if (r < 0)
                return r;

        usec_t end = usec_add(now(CLOCK_MONOTONIC), CONSOLE_ANSI_SEQUENCE_TIMEOUT_USEC);
        char buf[STRLEN(DCS_TERMINFO_R1) + MAX_TERMINFO_LENGTH + STRLEN(ANSI_ST)];
        size_t bytes = 0;

        for (;;) {
                usec_t n = now(CLOCK_MONOTONIC);
                if (n >= end)
                        return -EOPNOTSUPP;

                r = fd_wait_for_event(fd, POLLIN, usec_sub_unsigned(end, n));
                if (r < 0)
                        return r;
                if (r == 0)
                        return -EOPNOTSUPP;

                /* On the first read, read multiple characters, i.e. the shortest valid reply. Afterwards
                 * read byte by byte, since we don't want to read too much and drop characters from the input
                 * queue. */
                ssize_t l = read(fd, buf + bytes, bytes == 0 ? STRLEN(DCS_TERMINFO_R0) : 1);
                if (l < 0) {
                        if (errno == EAGAIN)
                                continue;
                        return -errno;
                }

                assert((size_t) l <= sizeof(buf) - bytes);
                bytes += l;

                r = scan_terminfo_response(buf, bytes, ret_name);
                if (r != -EAGAIN)
                        return r;

                if (bytes == sizeof(buf))
                        return -EOPNOTSUPP; /* The response has the right prefix, but we didn't find a valid
                                             * answer with a terminator in the allotted space. Something is
                                             * wrong, possibly some unrelated bytes got injected into the
                                             * answer. */
        }
}

int have_terminfo_file(const char *name) {
        /* This is a heuristic check if we have the file, using the directory layout used on
         * current Linux systems. Checks for other layouts can be added later if appropriate. */
        int r;

        assert(filename_is_valid(name));

        _cleanup_free_ char *p = path_join("/usr/share/terminfo", CHAR_TO_STR(name[0]), name);
        if (!p)
                return log_oom_debug();

        r = RET_NERRNO(access(p, F_OK));
        if (r == -ENOENT)
                return false;
        if (r < 0)
                return r;
        return true;
}

int query_term_for_tty(const char *tty, char **ret_term) {
        _cleanup_free_ char *dcs_term = NULL;
        int r;

        assert(tty);
        assert(ret_term);

        if (tty_is_vc_resolve(tty))
                return strdup_to(ret_term, "linux");

        /* Try to query the terminal implementation that we're on. This will not work in all
         * cases, which is fine, since this is intended to be used as a fallback. */

        _cleanup_close_ int tty_fd = open_terminal(tty, O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
        if (tty_fd < 0)
                return log_debug_errno(tty_fd, "Failed to open %s to query terminfo: %m", tty);

        r = terminal_get_terminfo_by_dcs(tty_fd, &dcs_term);
        if (r < 0)
                return log_debug_errno(r, "Failed to query %s for terminfo: %m", tty);

        r = have_terminfo_file(dcs_term);
        if (r < 0)
                return log_debug_errno(r, "Failed to look for terminfo %s: %m", dcs_term);
        if (r == 0)
                return log_info_errno(SYNTHETIC_ERRNO(ENODATA),
                                      "Terminfo %s not found for %s.", dcs_term, tty);

        *ret_term = TAKE_PTR(dcs_term);
        return 0;
}

int terminal_is_pty_fd(int fd) {
        int r;

        assert(fd >= 0);

        /* Returns true if we are looking at a pty, i.e. if it's backed by the /dev/pts/ file system */

        if (!isatty_safe(fd))
                return false;

        r = is_fs_type_at(fd, NULL, DEVPTS_SUPER_MAGIC);
        if (r != 0)
                return r;

        /* The ptmx device is weird, it exists twice, once inside and once outside devpts. To detect the
         * latter case, let's fire off an ioctl() that only works on ptmx devices. */

        int v;
        if (ioctl(fd, TIOCGPKT, &v) < 0) {
                if (ERRNO_IS_NOT_SUPPORTED(errno))
                        return false;

                return -errno;
        }

        return true;
}

int pty_open_peer(int fd, int mode) {
        assert(fd >= 0);

        /* Opens the peer PTY using the new race-free TIOCGPTPEER ioctl() (kernel 4.13).
         *
         * This is safe to be called on TTYs from other namespaces. */

        assert((mode & (O_CREAT|O_PATH|O_DIRECTORY|O_TMPFILE)) == 0);

        /* This replicates the EIO retry logic of open_terminal() in a modified way. */
        for (unsigned c = 0;; c++) {
                int peer_fd = ioctl(fd, TIOCGPTPEER, mode);
                if (peer_fd >= 0)
                        return peer_fd;

                if (errno != EIO)
                        return -errno;

                /* Max 1s in total */
                if (c >= 20)
                        return -EIO;

                (void) usleep_safe(50 * USEC_PER_MSEC);
        }
}

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