src/basic/terminal-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <limits.h>
   6 #include <linux/kd.h>
   7 #include <linux/tiocl.h>
   8 #include <linux/vt.h>
   9 #include <poll.h>
  10 #include <signal.h>
  11 #include <stdarg.h>
  12 #include <stddef.h>
  13 #include <stdlib.h>
  14 #include <sys/inotify.h>
  15 #include <sys/ioctl.h>
  16 #include <sys/sysmacros.h>
  17 #include <sys/time.h>
  18 #include <sys/types.h>
  19 #include <sys/utsname.h>
  20 #include <termios.h>
  21 #include <unistd.h>
  22
  23 #include "alloc-util.h"
  24 #include "def.h"
  25 #include "devnum-util.h"
  26 #include "env-util.h"
  27 #include "fd-util.h"
  28 #include "fileio.h"
  29 #include "fs-util.h"
  30 #include "inotify-util.h"
  31 #include "io-util.h"
  32 #include "log.h"
  33 #include "macro.h"
  34 #include "namespace-util.h"
  35 #include "parse-util.h"
  36 #include "path-util.h"
  37 #include "proc-cmdline.h"
  38 #include "process-util.h"
  39 #include "socket-util.h"
  40 #include "stat-util.h"
  41 #include "stdio-util.h"
  42 #include "string-util.h"
  43 #include "strv.h"
  44 #include "terminal-util.h"
  45 #include "time-util.h"
  46 #include "user-util.h"
  47 #include "util.h"
  48
  49 static volatile unsigned cached_columns = 0;
  50 static volatile unsigned cached_lines = 0;
  51
  52 static volatile int cached_on_tty = -1;
  53 static volatile int cached_color_mode = _COLOR_INVALID;
  54 static volatile int cached_underline_enabled = -1;
  55
  56 int chvt(int vt) {
  57         _cleanup_close_ int fd = -1;
  58
  59         /* Switch to the specified vt number. If the VT is specified <= 0 switch to the VT the kernel log messages go,
  60          * if that's configured. */
  61
  62         fd = open_terminal("/dev/tty0", O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
  63         if (fd < 0)
  64                 return -errno;
  65
  66         if (vt <= 0) {
  67                 int tiocl[2] = {
  68                         TIOCL_GETKMSGREDIRECT,
  69                         0
  70                 };
  71
  72                 if (ioctl(fd, TIOCLINUX, tiocl) < 0)
  73                         return -errno;
  74
  75                 vt = tiocl[0] <= 0 ? 1 : tiocl[0];
  76         }
  77
  78         return RET_NERRNO(ioctl(fd, VT_ACTIVATE, vt));
  79 }
  80
  81 int read_one_char(FILE *f, char *ret, usec_t t, bool *need_nl) {
  82         _cleanup_free_ char *line = NULL;
  83         struct termios old_termios;
  84         int r, fd;
  85
  86         assert(f);
  87         assert(ret);
  88
  89         /* If this is a terminal, then switch canonical mode off, so that we can read a single
  90          * character. (Note that fmemopen() streams do not have an fd associated with them, let's handle that
  91          * nicely.) */
  92         fd = fileno(f);
  93         if (fd >= 0 && tcgetattr(fd, &old_termios) >= 0) {
  94                 struct termios new_termios = old_termios;
  95
  96                 new_termios.c_lflag &= ~ICANON;
  97                 new_termios.c_cc[VMIN] = 1;
  98                 new_termios.c_cc[VTIME] = 0;
  99
 100                 if (tcsetattr(fd, TCSADRAIN, &new_termios) >= 0) {
 101                         char c;
 102
 103                         if (t != USEC_INFINITY) {
 104                                 if (fd_wait_for_event(fd, POLLIN, t) <= 0) {
 105                                         (void) tcsetattr(fd, TCSADRAIN, &old_termios);
 106                                         return -ETIMEDOUT;
 107                                 }
 108                         }
 109
 110                         r = safe_fgetc(f, &c);
 111                         (void) tcsetattr(fd, TCSADRAIN, &old_termios);
 112                         if (r < 0)
 113                                 return r;
 114                         if (r == 0)
 115                                 return -EIO;
 116
 117                         if (need_nl)
 118                                 *need_nl = c != '\n';
 119
 120                         *ret = c;
 121                         return 0;
 122                 }
 123         }
 124
 125         if (t != USEC_INFINITY && fd > 0) {
 126                 /* Let's wait the specified amount of time for input. When we have no fd we skip this, under
 127                  * the assumption that this is an fmemopen() stream or so where waiting doesn't make sense
 128                  * anyway, as the data is either already in the stream or cannot possible be placed there
 129                  * while we access the stream */
 130
 131                 if (fd_wait_for_event(fd, POLLIN, t) <= 0)
 132                         return -ETIMEDOUT;
 133         }
 134
 135         /* If this is not a terminal, then read a full line instead */
 136
 137         r = read_line(f, 16, &line); /* longer than necessary, to eat up UTF-8 chars/vt100 key sequences */
 138         if (r < 0)
 139                 return r;
 140         if (r == 0)
 141                 return -EIO;
 142
 143         if (strlen(line) != 1)
 144                 return -EBADMSG;
 145
 146         if (need_nl)
 147                 *need_nl = false;
 148
 149         *ret = line[0];
 150         return 0;
 151 }
 152
 153 #define DEFAULT_ASK_REFRESH_USEC (2*USEC_PER_SEC)
 154
 155 int ask_char(char *ret, const char *replies, const char *fmt, ...) {
 156         int r;
 157
 158         assert(ret);
 159         assert(replies);
 160         assert(fmt);
 161
 162         for (;;) {
 163                 va_list ap;
 164                 char c;
 165                 bool need_nl = true;
 166
 167                 fputs(ansi_highlight(), stdout);
 168
 169                 putchar('\r');
 170
 171                 va_start(ap, fmt);
 172                 vprintf(fmt, ap);
 173                 va_end(ap);
 174
 175                 fputs(ansi_normal(), stdout);
 176
 177                 fflush(stdout);
 178
 179                 r = read_one_char(stdin, &c, DEFAULT_ASK_REFRESH_USEC, &need_nl);
 180                 if (r < 0) {
 181
 182                         if (r == -ETIMEDOUT)
 183                                 continue;
 184
 185                         if (r == -EBADMSG) {
 186                                 puts("Bad input, please try again.");
 187                                 continue;
 188                         }
 189
 190                         putchar('\n');
 191                         return r;
 192                 }
 193
 194                 if (need_nl)
 195                         putchar('\n');
 196
 197                 if (strchr(replies, c)) {
 198                         *ret = c;
 199                         return 0;
 200                 }
 201
 202                 puts("Read unexpected character, please try again.");
 203         }
 204 }
 205
 206 int ask_string(char **ret, const char *text, ...) {
 207         _cleanup_free_ char *line = NULL;
 208         va_list ap;
 209         int r;
 210
 211         assert(ret);
 212         assert(text);
 213
 214         fputs(ansi_highlight(), stdout);
 215
 216         va_start(ap, text);
 217         vprintf(text, ap);
 218         va_end(ap);
 219
 220         fputs(ansi_normal(), stdout);
 221
 222         fflush(stdout);
 223
 224         r = read_line(stdin, LONG_LINE_MAX, &line);
 225         if (r < 0)
 226                 return r;
 227         if (r == 0)
 228                 return -EIO;
 229
 230         *ret = TAKE_PTR(line);
 231         return 0;
 232 }
 233
 234 int reset_terminal_fd(int fd, bool switch_to_text) {
 235         struct termios termios;
 236         int r = 0;
 237
 238         /* Set terminal to some sane defaults */
 239
 240         assert(fd >= 0);
 241
 242         if (isatty(fd) < 1)
 243                 return log_debug_errno(errno, "Asked to reset a terminal that actually isn't a terminal: %m");
 244
 245         /* We leave locked terminal attributes untouched, so that Plymouth may set whatever it wants to set,
 246          * and we don't interfere with that. */
 247
 248         /* Disable exclusive mode, just in case */
 249         if (ioctl(fd, TIOCNXCL) < 0)
 250                 log_debug_errno(errno, "TIOCNXCL ioctl failed on TTY, ignoring: %m");
 251
 252         /* Switch to text mode */
 253         if (switch_to_text)
 254                 if (ioctl(fd, KDSETMODE, KD_TEXT) < 0)
 255                         log_debug_errno(errno, "KDSETMODE ioctl for switching to text mode failed on TTY, ignoring: %m");
 256
 257
 258         /* Set default keyboard mode */
 259         (void) vt_reset_keyboard(fd);
 260
 261         if (tcgetattr(fd, &termios) < 0) {
 262                 r = log_debug_errno(errno, "Failed to get terminal parameters: %m");
 263                 goto finish;
 264         }
 265
 266         /* We only reset the stuff that matters to the software. How
 267          * hardware is set up we don't touch assuming that somebody
 268          * else will do that for us */
 269
 270         termios.c_iflag &= ~(IGNBRK | BRKINT | ISTRIP | INLCR | IGNCR | IUCLC);
 271         termios.c_iflag |= ICRNL | IMAXBEL | IUTF8;
 272         termios.c_oflag |= ONLCR;
 273         termios.c_cflag |= CREAD;
 274         termios.c_lflag = ISIG | ICANON | IEXTEN | ECHO | ECHOE | ECHOK | ECHOCTL | ECHOPRT | ECHOKE;
 275
 276         termios.c_cc[VINTR]    =   03;  /* ^C */
 277         termios.c_cc[VQUIT]    =  034;  /* ^\ */
 278         termios.c_cc[VERASE]   = 0177;
 279         termios.c_cc[VKILL]    =  025;  /* ^X */
 280         termios.c_cc[VEOF]     =   04;  /* ^D */
 281         termios.c_cc[VSTART]   =  021;  /* ^Q */
 282         termios.c_cc[VSTOP]    =  023;  /* ^S */
 283         termios.c_cc[VSUSP]    =  032;  /* ^Z */
 284         termios.c_cc[VLNEXT]   =  026;  /* ^V */
 285         termios.c_cc[VWERASE]  =  027;  /* ^W */
 286         termios.c_cc[VREPRINT] =  022;  /* ^R */
 287         termios.c_cc[VEOL]     =    0;
 288         termios.c_cc[VEOL2]    =    0;
 289
 290         termios.c_cc[VTIME]  = 0;
 291         termios.c_cc[VMIN]   = 1;
 292
 293         if (tcsetattr(fd, TCSANOW, &termios) < 0)
 294                 r = -errno;
 295
 296 finish:
 297         /* Just in case, flush all crap out */
 298         (void) tcflush(fd, TCIOFLUSH);
 299
 300         return r;
 301 }
 302
 303 int reset_terminal(const char *name) {
 304         _cleanup_close_ int fd = -1;
 305
 306         /* We open the terminal with O_NONBLOCK here, to ensure we
 307          * don't block on carrier if this is a terminal with carrier
 308          * configured. */
 309
 310         fd = open_terminal(name, O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
 311         if (fd < 0)
 312                 return fd;
 313
 314         return reset_terminal_fd(fd, true);
 315 }
 316
 317 int open_terminal(const char *name, int mode) {
 318         _cleanup_close_ int fd = -1;
 319         unsigned c = 0;
 320
 321         /*
 322          * If a TTY is in the process of being closed opening it might cause EIO. This is horribly awful, but
 323          * unlikely to be changed in the kernel. Hence we work around this problem by retrying a couple of
 324          * times.
 325          *
 326          * https://bugs.launchpad.net/ubuntu/+source/linux/+bug/554172/comments/245
 327          */
 328
 329         if (mode & O_CREAT)
 330                 return -EINVAL;
 331
 332         for (;;) {
 333                 fd = open(name, mode, 0);
 334                 if (fd >= 0)
 335                         break;
 336
 337                 if (errno != EIO)
 338                         return -errno;
 339
 340                 /* Max 1s in total */
 341                 if (c >= 20)
 342                         return -errno;
 343
 344                 (void) usleep(50 * USEC_PER_MSEC);
 345                 c++;
 346         }
 347
 348         if (isatty(fd) < 1)
 349                 return negative_errno();
 350
 351         return TAKE_FD(fd);
 352 }
 353
 354 int acquire_terminal(
 355                 const char *name,
 356                 AcquireTerminalFlags flags,
 357                 usec_t timeout) {
 358
 359         _cleanup_close_ int notify = -1, fd = -1;
 360         usec_t ts = USEC_INFINITY;
 361         int r, wd = -1;
 362
 363         assert(name);
 364         assert(IN_SET(flags & ~ACQUIRE_TERMINAL_PERMISSIVE, ACQUIRE_TERMINAL_TRY, ACQUIRE_TERMINAL_FORCE, ACQUIRE_TERMINAL_WAIT));
 365
 366         /* We use inotify to be notified when the tty is closed. We create the watch before checking if we can actually
 367          * acquire it, so that we don't lose any event.
 368          *
 369          * Note: strictly speaking this actually watches for the device being closed, it does *not* really watch
 370          * whether a tty loses its controlling process. However, unless some rogue process uses TIOCNOTTY on /dev/tty
 371          * *after* closing its tty otherwise this will not become a problem. As long as the administrator makes sure to
 372          * not configure any service on the same tty as an untrusted user this should not be a problem. (Which they
 373          * probably should not do anyway.) */
 374
 375         if ((flags & ~ACQUIRE_TERMINAL_PERMISSIVE) == ACQUIRE_TERMINAL_WAIT) {
 376                 notify = inotify_init1(IN_CLOEXEC | (timeout != USEC_INFINITY ? IN_NONBLOCK : 0));
 377                 if (notify < 0)
 378                         return -errno;
 379
 380                 wd = inotify_add_watch(notify, name, IN_CLOSE);
 381                 if (wd < 0)
 382                         return -errno;
 383
 384                 if (timeout != USEC_INFINITY)
 385                         ts = now(CLOCK_MONOTONIC);
 386         }
 387
 388         for (;;) {
 389                 struct sigaction sa_old, sa_new = {
 390                         .sa_handler = SIG_IGN,
 391                         .sa_flags = SA_RESTART,
 392                 };
 393
 394                 if (notify >= 0) {
 395                         r = flush_fd(notify);
 396                         if (r < 0)
 397                                 return r;
 398                 }
 399
 400                 /* We pass here O_NOCTTY only so that we can check the return value TIOCSCTTY and have a reliable way
 401                  * to figure out if we successfully became the controlling process of the tty */
 402                 fd = open_terminal(name, O_RDWR|O_NOCTTY|O_CLOEXEC);
 403                 if (fd < 0)
 404                         return fd;
 405
 406                 /* Temporarily ignore SIGHUP, so that we don't get SIGHUP'ed if we already own the tty. */
 407                 assert_se(sigaction(SIGHUP, &sa_new, &sa_old) == 0);
 408
 409                 /* First, try to get the tty */
 410                 r = RET_NERRNO(ioctl(fd, TIOCSCTTY, (flags & ~ACQUIRE_TERMINAL_PERMISSIVE) == ACQUIRE_TERMINAL_FORCE));
 411
 412                 /* Reset signal handler to old value */
 413                 assert_se(sigaction(SIGHUP, &sa_old, NULL) == 0);
 414
 415                 /* Success? Exit the loop now! */
 416                 if (r >= 0)
 417                         break;
 418
 419                 /* Any failure besides -EPERM? Fail, regardless of the mode. */
 420                 if (r != -EPERM)
 421                         return r;
 422
 423                 if (flags & ACQUIRE_TERMINAL_PERMISSIVE) /* If we are in permissive mode, then EPERM is fine, turn this
 424                                                           * into a success. Note that EPERM is also returned if we
 425                                                           * already are the owner of the TTY. */
 426                         break;
 427
 428                 if (flags != ACQUIRE_TERMINAL_WAIT) /* If we are in TRY or FORCE mode, then propagate EPERM as EPERM */
 429                         return r;
 430
 431                 assert(notify >= 0);
 432                 assert(wd >= 0);
 433
 434                 for (;;) {
 435                         union inotify_event_buffer buffer;
 436                         ssize_t l;
 437
 438                         if (timeout != USEC_INFINITY) {
 439                                 usec_t n;
 440
 441                                 assert(ts != USEC_INFINITY);
 442
 443                                 n = usec_sub_unsigned(now(CLOCK_MONOTONIC), ts);
 444                                 if (n >= timeout)
 445                                         return -ETIMEDOUT;
 446
 447                                 r = fd_wait_for_event(notify, POLLIN, usec_sub_unsigned(timeout, n));
 448                                 if (r < 0)
 449                                         return r;
 450                                 if (r == 0)
 451                                         return -ETIMEDOUT;
 452                         }
 453
 454                         l = read(notify, &buffer, sizeof(buffer));
 455                         if (l < 0) {
 456                                 if (ERRNO_IS_TRANSIENT(errno))
 457                                         continue;
 458
 459                                 return -errno;
 460                         }
 461
 462                         FOREACH_INOTIFY_EVENT(e, buffer, l) {
 463                                 if (e->mask & IN_Q_OVERFLOW) /* If we hit an inotify queue overflow, simply check if the terminal is up for grabs now. */
 464                                         break;
 465
 466                                 if (e->wd != wd || !(e->mask & IN_CLOSE)) /* Safety checks */
 467                                         return -EIO;
 468                         }
 469
 470                         break;
 471                 }
 472
 473                 /* We close the tty fd here since if the old session ended our handle will be dead. It's important that
 474                  * we do this after sleeping, so that we don't enter an endless loop. */
 475                 fd = safe_close(fd);
 476         }
 477
 478         return TAKE_FD(fd);
 479 }
 480
 481 int release_terminal(void) {
 482         static const struct sigaction sa_new = {
 483                 .sa_handler = SIG_IGN,
 484                 .sa_flags = SA_RESTART,
 485         };
 486
 487         _cleanup_close_ int fd = -1;
 488         struct sigaction sa_old;
 489         int r;
 490
 491         fd = open("/dev/tty", O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
 492         if (fd < 0)
 493                 return -errno;
 494
 495         /* Temporarily ignore SIGHUP, so that we don't get SIGHUP'ed
 496          * by our own TIOCNOTTY */
 497         assert_se(sigaction(SIGHUP, &sa_new, &sa_old) == 0);
 498
 499         r = RET_NERRNO(ioctl(fd, TIOCNOTTY));
 500
 501         assert_se(sigaction(SIGHUP, &sa_old, NULL) == 0);
 502
 503         return r;
 504 }
 505
 506 int terminal_vhangup_fd(int fd) {
 507         assert(fd >= 0);
 508         return RET_NERRNO(ioctl(fd, TIOCVHANGUP));
 509 }
 510
 511 int terminal_vhangup(const char *name) {
 512         _cleanup_close_ int fd = -1;
 513
 514         fd = open_terminal(name, O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
 515         if (fd < 0)
 516                 return fd;
 517
 518         return terminal_vhangup_fd(fd);
 519 }
 520
 521 int vt_disallocate(const char *name) {
 522         const char *e;
 523         int r;
 524
 525         /* Deallocate the VT if possible. If not possible
 526          * (i.e. because it is the active one), at least clear it
 527          * entirely (including the scrollback buffer). */
 528
 529         e = path_startswith(name, "/dev/");
 530         if (!e)
 531                 return -EINVAL;
 532
 533         if (tty_is_vc(name)) {
 534                 _cleanup_close_ int fd = -1;
 535                 unsigned u;
 536                 const char *n;
 537
 538                 n = startswith(e, "tty");
 539                 if (!n)
 540                         return -EINVAL;
 541
 542                 r = safe_atou(n, &u);
 543                 if (r < 0)
 544                         return r;
 545
 546                 if (u <= 0)
 547                         return -EINVAL;
 548
 549                 /* Try to deallocate */
 550                 fd = open_terminal("/dev/tty0", O_RDWR|O_NOCTTY|O_CLOEXEC|O_NONBLOCK);
 551                 if (fd < 0)
 552                         return fd;
 553
 554                 r = ioctl(fd, VT_DISALLOCATE, u);
 555                 if (r >= 0)
 556                         return 0;
 557                 if (errno != EBUSY)
 558                         return -errno;
 559         }
 560
 561         /* So this is not a VT (in which case we cannot deallocate it),
 562          * or we failed to deallocate. Let's at least clear the screen. */
 563
 564         _cleanup_close_ int fd2 = open_terminal(name, O_RDWR|O_NOCTTY|O_CLOEXEC);
 565         if (fd2 < 0)
 566                 return fd2;
 567
 568         (void) loop_write(fd2,
 569                           "\033[r"   /* clear scrolling region */
 570                           "\033[H"   /* move home */
 571                           "\033[3J", /* clear screen including scrollback, requires Linux 2.6.40 */
 572                           10, false);
 573         return 0;
 574 }
 575
 576 int make_console_stdio(void) {
 577         int fd, r;
 578
 579         /* Make /dev/console the controlling terminal and stdin/stdout/stderr, if we can. If we can't use
 580          * /dev/null instead. This is particularly useful if /dev/console is turned off, e.g. if console=null
 581          * is specified on the kernel command line. */
 582
 583         fd = acquire_terminal("/dev/console", ACQUIRE_TERMINAL_FORCE|ACQUIRE_TERMINAL_PERMISSIVE, USEC_INFINITY);
 584         if (fd < 0) {
 585                 log_warning_errno(fd, "Failed to acquire terminal, using /dev/null stdin/stdout/stderr instead: %m");
 586
 587                 r = make_null_stdio();
 588                 if (r < 0)
 589                         return log_error_errno(r, "Failed to make /dev/null stdin/stdout/stderr: %m");
 590
 591         } else {
 592                 r = reset_terminal_fd(fd, true);
 593                 if (r < 0)
 594                         log_warning_errno(r, "Failed to reset terminal, ignoring: %m");
 595
 596                 r = rearrange_stdio(fd, fd, fd); /* This invalidates 'fd' both on success and on failure. */
 597                 if (r < 0)
 598                         return log_error_errno(r, "Failed to make terminal stdin/stdout/stderr: %m");
 599         }
 600
 601         reset_terminal_feature_caches();
 602         return 0;
 603 }
 604
 605 bool tty_is_vc(const char *tty) {
 606         assert(tty);
 607
 608         return vtnr_from_tty(tty) >= 0;
 609 }
 610
 611 bool tty_is_console(const char *tty) {
 612         assert(tty);
 613
 614         return streq(skip_dev_prefix(tty), "console");
 615 }
 616
 617 int vtnr_from_tty(const char *tty) {
 618         int i, r;
 619
 620         assert(tty);
 621
 622         tty = skip_dev_prefix(tty);
 623
 624         if (!startswith(tty, "tty") )
 625                 return -EINVAL;
 626
 627         if (tty[3] < '0' || tty[3] > '9')
 628                 return -EINVAL;
 629
 630         r = safe_atoi(tty+3, &i);
 631         if (r < 0)
 632                 return r;
 633
 634         if (i < 0 || i > 63)
 635                 return -EINVAL;
 636
 637         return i;
 638 }
 639
 640  int resolve_dev_console(char **ret) {
 641         _cleanup_free_ char *active = NULL;
 642         char *tty;
 643         int r;
 644
 645         assert(ret);
 646
 647         /* Resolve where /dev/console is pointing to, if /sys is actually ours (i.e. not read-only-mounted which is a
 648          * sign for container setups) */
 649
 650         if (path_is_read_only_fs("/sys") > 0)
 651                 return -ENOMEDIUM;
 652
 653         r = read_one_line_file("/sys/class/tty/console/active", &active);
 654         if (r < 0)
 655                 return r;
 656
 657         /* If multiple log outputs are configured the last one is what /dev/console points to */
 658         tty = strrchr(active, ' ');
 659         if (tty)
 660                 tty++;
 661         else
 662                 tty = active;
 663
 664         if (streq(tty, "tty0")) {
 665                 active = mfree(active);
 666
 667                 /* Get the active VC (e.g. tty1) */
 668                 r = read_one_line_file("/sys/class/tty/tty0/active", &active);
 669                 if (r < 0)
 670                         return r;
 671
 672                 tty = active;
 673         }
 674
 675         if (tty == active)
 676                 *ret = TAKE_PTR(active);
 677         else {
 678                 char *tmp;
 679
 680                 tmp = strdup(tty);
 681                 if (!tmp)
 682                         return -ENOMEM;
 683
 684                 *ret = tmp;
 685         }
 686
 687         return 0;
 688 }
 689
 690 int get_kernel_consoles(char ***ret) {
 691         _cleanup_strv_free_ char **l = NULL;
 692         _cleanup_free_ char *line = NULL;
 693         const char *p;
 694         int r;
 695
 696         assert(ret);
 697
 698         /* If /sys is mounted read-only this means we are running in some kind of container environment. In that
 699          * case /sys would reflect the host system, not us, hence ignore the data we can read from it. */
 700         if (path_is_read_only_fs("/sys") > 0)
 701                 goto fallback;
 702
 703         r = read_one_line_file("/sys/class/tty/console/active", &line);
 704         if (r < 0)
 705                 return r;
 706
 707         p = line;
 708         for (;;) {
 709                 _cleanup_free_ char *tty = NULL, *path = NULL;
 710
 711                 r = extract_first_word(&p, &tty, NULL, 0);
 712                 if (r < 0)
 713                         return r;
 714                 if (r == 0)
 715                         break;
 716
 717                 if (streq(tty, "tty0")) {
 718                         tty = mfree(tty);
 719                         r = read_one_line_file("/sys/class/tty/tty0/active", &tty);
 720                         if (r < 0)
 721                                 return r;
 722                 }
 723
 724                 path = path_join("/dev", tty);
 725                 if (!path)
 726                         return -ENOMEM;
 727
 728                 if (access(path, F_OK) < 0) {
 729                         log_debug_errno(errno, "Console device %s is not accessible, skipping: %m", path);
 730                         continue;
 731                 }
 732
 733                 r = strv_consume(&l, TAKE_PTR(path));
 734                 if (r < 0)
 735                         return r;
 736         }
 737
 738         if (strv_isempty(l)) {
 739                 log_debug("No devices found for system console");
 740                 goto fallback;
 741         }
 742
 743         *ret = TAKE_PTR(l);
 744
 745         return 0;
 746
 747 fallback:
 748         r = strv_extend(&l, "/dev/console");
 749         if (r < 0)
 750                 return r;
 751
 752         *ret = TAKE_PTR(l);
 753
 754         return 0;
 755 }
 756
 757 bool tty_is_vc_resolve(const char *tty) {
 758         _cleanup_free_ char *resolved = NULL;
 759
 760         assert(tty);
 761
 762         tty = skip_dev_prefix(tty);
 763
 764         if (streq(tty, "console")) {
 765                 if (resolve_dev_console(&resolved) < 0)
 766                         return false;
 767
 768                 tty = resolved;
 769         }
 770
 771         return tty_is_vc(tty);
 772 }
 773
 774 const char *default_term_for_tty(const char *tty) {
 775         return tty && tty_is_vc_resolve(tty) ? "linux" : "vt220";
 776 }
 777
 778 int fd_columns(int fd) {
 779         struct winsize ws = {};
 780
 781         if (fd < 0)
 782                 return -EBADF;
 783
 784         if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
 785                 return -errno;
 786
 787         if (ws.ws_col <= 0)
 788                 return -EIO;
 789
 790         return ws.ws_col;
 791 }
 792
 793 unsigned columns(void) {
 794         const char *e;
 795         int c;
 796
 797         if (cached_columns > 0)
 798                 return cached_columns;
 799
 800         c = 0;
 801         e = getenv("COLUMNS");
 802         if (e)
 803                 (void) safe_atoi(e, &c);
 804
 805         if (c <= 0 || c > USHRT_MAX) {
 806                 c = fd_columns(STDOUT_FILENO);
 807                 if (c <= 0)
 808                         c = 80;
 809         }
 810
 811         cached_columns = c;
 812         return cached_columns;
 813 }
 814
 815 int fd_lines(int fd) {
 816         struct winsize ws = {};
 817
 818         if (fd < 0)
 819                 return -EBADF;
 820
 821         if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
 822                 return -errno;
 823
 824         if (ws.ws_row <= 0)
 825                 return -EIO;
 826
 827         return ws.ws_row;
 828 }
 829
 830 unsigned lines(void) {
 831         const char *e;
 832         int l;
 833
 834         if (cached_lines > 0)
 835                 return cached_lines;
 836
 837         l = 0;
 838         e = getenv("LINES");
 839         if (e)
 840                 (void) safe_atoi(e, &l);
 841
 842         if (l <= 0 || l > USHRT_MAX) {
 843                 l = fd_lines(STDOUT_FILENO);
 844                 if (l <= 0)
 845                         l = 24;
 846         }
 847
 848         cached_lines = l;
 849         return cached_lines;
 850 }
 851
 852 int terminal_set_size_fd(int fd, const char *ident, unsigned rows, unsigned cols) {
 853         struct winsize ws;
 854
 855         if (rows == UINT_MAX && cols == UINT_MAX)
 856                 return 0;
 857
 858         if (ioctl(fd, TIOCGWINSZ, &ws) < 0)
 859                 return log_debug_errno(errno,
 860                                        "TIOCGWINSZ ioctl for getting %s size failed, not setting terminal size: %m",
 861                                        ident ?: "TTY");
 862
 863         if (rows == UINT_MAX)
 864                 rows = ws.ws_row;
 865         else if (rows > USHRT_MAX)
 866                 rows = USHRT_MAX;
 867
 868         if (cols == UINT_MAX)
 869                 cols = ws.ws_col;
 870         else if (cols > USHRT_MAX)
 871                 cols = USHRT_MAX;
 872
 873         if (rows == ws.ws_row && cols == ws.ws_col)
 874                 return 0;
 875
 876         ws.ws_row = rows;
 877         ws.ws_col = cols;
 878
 879         if (ioctl(fd, TIOCSWINSZ, &ws) < 0)
 880                 return log_debug_errno(errno, "TIOCSWINSZ ioctl for setting %s size failed: %m", ident ?: "TTY");
 881
 882         return 0;
 883 }
 884
 885 /* intended to be used as a SIGWINCH sighandler */
 886 void columns_lines_cache_reset(int signum) {
 887         cached_columns = 0;
 888         cached_lines = 0;
 889 }
 890
 891 void reset_terminal_feature_caches(void) {
 892         cached_columns = 0;
 893         cached_lines = 0;
 894
 895         cached_color_mode = _COLOR_INVALID;
 896         cached_underline_enabled = -1;
 897         cached_on_tty = -1;
 898 }
 899
 900 bool on_tty(void) {
 901
 902         /* We check both stdout and stderr, so that situations where pipes on the shell are used are reliably
 903          * recognized, regardless if only the output or the errors are piped to some place. Since on_tty() is generally
 904          * used to default to a safer, non-interactive, non-color mode of operation it's probably good to be defensive
 905          * here, and check for both. Note that we don't check for STDIN_FILENO, because it should fine to use fancy
 906          * terminal functionality when outputting stuff, even if the input is piped to us. */
 907
 908         if (cached_on_tty < 0)
 909                 cached_on_tty =
 910                         isatty(STDOUT_FILENO) > 0 &&
 911                         isatty(STDERR_FILENO) > 0;
 912
 913         return cached_on_tty;
 914 }
 915
 916 int getttyname_malloc(int fd, char **ret) {
 917         char path[PATH_MAX], *c; /* PATH_MAX is counted *with* the trailing NUL byte */
 918         int r;
 919
 920         assert(fd >= 0);
 921         assert(ret);
 922
 923         r = ttyname_r(fd, path, sizeof path); /* positive error */
 924         assert(r >= 0);
 925         if (r == ERANGE)
 926                 return -ENAMETOOLONG;
 927         if (r > 0)
 928                 return -r;
 929
 930         c = strdup(skip_dev_prefix(path));
 931         if (!c)
 932                 return -ENOMEM;
 933
 934         *ret = c;
 935         return 0;
 936 }
 937
 938 int getttyname_harder(int fd, char **ret) {
 939         _cleanup_free_ char *s = NULL;
 940         int r;
 941
 942         r = getttyname_malloc(fd, &s);
 943         if (r < 0)
 944                 return r;
 945
 946         if (streq(s, "tty"))
 947                 return get_ctty(0, NULL, ret);
 948
 949         *ret = TAKE_PTR(s);
 950         return 0;
 951 }
 952
 953 int get_ctty_devnr(pid_t pid, dev_t *d) {
 954         int r;
 955         _cleanup_free_ char *line = NULL;
 956         const char *p;
 957         unsigned long ttynr;
 958
 959         assert(pid >= 0);
 960
 961         p = procfs_file_alloca(pid, "stat");
 962         r = read_one_line_file(p, &line);
 963         if (r < 0)
 964                 return r;
 965
 966         p = strrchr(line, ')');
 967         if (!p)
 968                 return -EIO;
 969
 970         p++;
 971
 972         if (sscanf(p, " "
 973                    "%*c "  /* state */
 974                    "%*d "  /* ppid */
 975                    "%*d "  /* pgrp */
 976                    "%*d "  /* session */
 977                    "%lu ", /* ttynr */
 978                    &ttynr) != 1)
 979                 return -EIO;
 980
 981         if (major(ttynr) == 0 && minor(ttynr) == 0)
 982                 return -ENXIO;
 983
 984         if (d)
 985                 *d = (dev_t) ttynr;
 986
 987         return 0;
 988 }
 989
 990 int get_ctty(pid_t pid, dev_t *ret_devnr, char **ret) {
 991         char pty[STRLEN("/dev/pts/") + DECIMAL_STR_MAX(dev_t) + 1];
 992         _cleanup_free_ char *buf = NULL;
 993         const char *fn = NULL, *w;
 994         dev_t devnr;
 995         int r;
 996
 997         r = get_ctty_devnr(pid, &devnr);
 998         if (r < 0)
 999                 return r;
1000
1001         r = device_path_make_canonical(S_IFCHR, devnr, &buf);
1002         if (r < 0) {
1003                 struct stat st;
1004
1005                 if (r != -ENOENT) /* No symlink for this in /dev/char/? */
1006                         return r;
1007
1008                 /* Maybe this is PTY? PTY devices are not listed in /dev/char/, as they don't follow the
1009                  * Linux device model and hence device_path_make_canonical() doesn't work for them. Let's
1010                  * assume this is a PTY for a moment, and check if the device node this would then map to in
1011                  * /dev/pts/ matches the one we are looking for. This way we don't have to hardcode the major
1012                  * number (which is 136 btw), but we still rely on the fact that PTY numbers map directly to
1013                  * the minor number of the pty. */
1014                 xsprintf(pty, "/dev/pts/%u", minor(devnr));
1015
1016                 if (stat(pty, &st) < 0) {
1017                         if (errno != ENOENT)
1018                                 return -errno;
1019
1020                 } else if (S_ISCHR(st.st_mode) && devnr == st.st_rdev) /* Bingo! */
1021                         fn = pty;
1022
1023                 if (!fn) {
1024                         /* Doesn't exist, or not a PTY? Probably something similar to the PTYs which have no
1025                          * symlink in /dev/char/. Let's return something vaguely useful. */
1026                         r = device_path_make_major_minor(S_IFCHR, devnr, &buf);
1027                         if (r < 0)
1028                                 return r;
1029
1030                         fn = buf;
1031                 }
1032         } else
1033                 fn = buf;
1034
1035         w = path_startswith(fn, "/dev/");
1036         if (!w)
1037                 return -EINVAL;
1038
1039         if (ret) {
1040                 _cleanup_free_ char *b = NULL;
1041
1042                 b = strdup(w);
1043                 if (!b)
1044                         return -ENOMEM;
1045
1046                 *ret = TAKE_PTR(b);
1047         }
1048
1049         if (ret_devnr)
1050                 *ret_devnr = devnr;
1051
1052         return 0;
1053 }
1054
1055 int ptsname_malloc(int fd, char **ret) {
1056         size_t l = 100;
1057
1058         assert(fd >= 0);
1059         assert(ret);
1060
1061         for (;;) {
1062                 char *c;
1063
1064                 c = new(char, l);
1065                 if (!c)
1066                         return -ENOMEM;
1067
1068                 if (ptsname_r(fd, c, l) == 0) {
1069                         *ret = c;
1070                         return 0;
1071                 }
1072                 if (errno != ERANGE) {
1073                         free(c);
1074                         return -errno;
1075                 }
1076
1077                 free(c);
1078
1079                 if (l > SIZE_MAX / 2)
1080                         return -ENOMEM;
1081
1082                 l *= 2;
1083         }
1084 }
1085
1086 int openpt_allocate(int flags, char **ret_slave) {
1087         _cleanup_close_ int fd = -1;
1088         _cleanup_free_ char *p = NULL;
1089         int r;
1090
1091         fd = posix_openpt(flags|O_NOCTTY|O_CLOEXEC);
1092         if (fd < 0)
1093                 return -errno;
1094
1095         if (ret_slave) {
1096                 r = ptsname_malloc(fd, &p);
1097                 if (r < 0)
1098                         return r;
1099
1100                 if (!path_startswith(p, "/dev/pts/"))
1101                         return -EINVAL;
1102         }
1103
1104         if (unlockpt(fd) < 0)
1105                 return -errno;
1106
1107         if (ret_slave)
1108                 *ret_slave = TAKE_PTR(p);
1109
1110         return TAKE_FD(fd);
1111 }
1112
1113 static int ptsname_namespace(int pty, char **ret) {
1114         int no = -1, r;
1115
1116         /* Like ptsname(), but doesn't assume that the path is
1117          * accessible in the local namespace. */
1118
1119         r = ioctl(pty, TIOCGPTN, &no);
1120         if (r < 0)
1121                 return -errno;
1122
1123         if (no < 0)
1124                 return -EIO;
1125
1126         if (asprintf(ret, "/dev/pts/%i", no) < 0)
1127                 return -ENOMEM;
1128
1129         return 0;
1130 }
1131
1132 int openpt_allocate_in_namespace(pid_t pid, int flags, char **ret_slave) {
1133         _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, usernsfd = -1, rootfd = -1, fd = -1;
1134         _cleanup_close_pair_ int pair[2] = { -1, -1 };
1135         pid_t child;
1136         int r;
1137
1138         assert(pid > 0);
1139
1140         r = namespace_open(pid, &pidnsfd, &mntnsfd, NULL, &usernsfd, &rootfd);
1141         if (r < 0)
1142                 return r;
1143
1144         if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
1145                 return -errno;
1146
1147         r = namespace_fork("(sd-openptns)", "(sd-openpt)", NULL, 0, FORK_RESET_SIGNALS|FORK_DEATHSIG,
1148                            pidnsfd, mntnsfd, -1, usernsfd, rootfd, &child);
1149         if (r < 0)
1150                 return r;
1151         if (r == 0) {
1152                 pair[0] = safe_close(pair[0]);
1153
1154                 fd = openpt_allocate(flags, NULL);
1155                 if (fd < 0)
1156                         _exit(EXIT_FAILURE);
1157
1158                 if (send_one_fd(pair[1], fd, 0) < 0)
1159                         _exit(EXIT_FAILURE);
1160
1161                 _exit(EXIT_SUCCESS);
1162         }
1163
1164         pair[1] = safe_close(pair[1]);
1165
1166         r = wait_for_terminate_and_check("(sd-openptns)", child, 0);
1167         if (r < 0)
1168                 return r;
1169         if (r != EXIT_SUCCESS)
1170                 return -EIO;
1171
1172         fd = receive_one_fd(pair[0], 0);
1173         if (fd < 0)
1174                 return fd;
1175
1176         if (ret_slave) {
1177                 r = ptsname_namespace(fd, ret_slave);
1178                 if (r < 0)
1179                         return r;
1180         }
1181
1182         return TAKE_FD(fd);
1183 }
1184
1185 int open_terminal_in_namespace(pid_t pid, const char *name, int mode) {
1186         _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, usernsfd = -1, rootfd = -1;
1187         _cleanup_close_pair_ int pair[2] = { -1, -1 };
1188         pid_t child;
1189         int r;
1190
1191         r = namespace_open(pid, &pidnsfd, &mntnsfd, NULL, &usernsfd, &rootfd);
1192         if (r < 0)
1193                 return r;
1194
1195         if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
1196                 return -errno;
1197
1198         r = namespace_fork("(sd-terminalns)", "(sd-terminal)", NULL, 0, FORK_RESET_SIGNALS|FORK_DEATHSIG,
1199                            pidnsfd, mntnsfd, -1, usernsfd, rootfd, &child);
1200         if (r < 0)
1201                 return r;
1202         if (r == 0) {
1203                 int master;
1204
1205                 pair[0] = safe_close(pair[0]);
1206
1207                 master = open_terminal(name, mode|O_NOCTTY|O_CLOEXEC);
1208                 if (master < 0)
1209                         _exit(EXIT_FAILURE);
1210
1211                 if (send_one_fd(pair[1], master, 0) < 0)
1212                         _exit(EXIT_FAILURE);
1213
1214                 _exit(EXIT_SUCCESS);
1215         }
1216
1217         pair[1] = safe_close(pair[1]);
1218
1219         r = wait_for_terminate_and_check("(sd-terminalns)", child, 0);
1220         if (r < 0)
1221                 return r;
1222         if (r != EXIT_SUCCESS)
1223                 return -EIO;
1224
1225         return receive_one_fd(pair[0], 0);
1226 }
1227
1228 static bool getenv_terminal_is_dumb(void) {
1229         const char *e;
1230
1231         e = getenv("TERM");
1232         if (!e)
1233                 return true;
1234
1235         return streq(e, "dumb");
1236 }
1237
1238 bool terminal_is_dumb(void) {
1239         if (!on_tty())
1240                 return true;
1241
1242         return getenv_terminal_is_dumb();
1243 }
1244
1245 static ColorMode parse_systemd_colors(void) {
1246         const char *e;
1247         int r;
1248
1249         e = getenv("SYSTEMD_COLORS");
1250         if (!e)
1251                 return _COLOR_INVALID;
1252         if (streq(e, "16"))
1253                 return COLOR_16;
1254         if (streq(e, "256"))
1255                 return COLOR_256;
1256         r = parse_boolean(e);
1257         if (r >= 0)
1258                 return r > 0 ? COLOR_ON : COLOR_OFF;
1259         return _COLOR_INVALID;
1260 }
1261
1262 ColorMode get_color_mode(void) {
1263
1264         /* Returns the mode used to choose output colors. The possible modes are COLOR_OFF for no colors,
1265          * COLOR_16 for only the base 16 ANSI colors, COLOR_256 for more colors and COLOR_ON for unrestricted
1266          * color output. For that we check $SYSTEMD_COLORS first (which is the explicit way to
1267          * change the mode). If that didn't work we turn colors off unless we are on a TTY. And if we are on a TTY
1268          * we turn it off if $TERM is set to "dumb". There's one special tweak though: if we are PID 1 then we do not
1269          * check whether we are connected to a TTY, because we don't keep /dev/console open continuously due to fear
1270          * of SAK, and hence things are a bit weird. */
1271         ColorMode m;
1272
1273         if (cached_color_mode < 0) {
1274                 m = parse_systemd_colors();
1275                 if (m >= 0)
1276                         cached_color_mode = m;
1277                 else if (getenv("NO_COLOR"))
1278                         /* We only check for the presence of the variable; value is ignored. */
1279                         cached_color_mode = COLOR_OFF;
1280
1281                 else if (getpid_cached() == 1) {
1282                         /* PID1 outputs to the console without holding it open all the time.
1283                          *
1284                          * Note that the Linux console can only display 16 colors. We still enable 256 color
1285                          * mode even for PID1 output though (which typically goes to the Linux console),
1286                          * since the Linux console is able to parse the 256 color sequences and automatically
1287                          * map them to the closest color in the 16 color palette (since kernel 3.16). Doing
1288                          * 256 colors is nice for people who invoke systemd in a container or via a serial
1289                          * link or such, and use a true 256 color terminal to do so. */
1290                         if (getenv_terminal_is_dumb())
1291                                 cached_color_mode = COLOR_OFF;
1292                 } else {
1293                         if (terminal_is_dumb())
1294                                 cached_color_mode = COLOR_OFF;
1295                 }
1296
1297                 if (cached_color_mode < 0) {
1298                         /* We failed to figure out any reason to *disable* colors.
1299                          * Let's see how many colors we shall use. */
1300                         if (STRPTR_IN_SET(getenv("COLORTERM"),
1301                                           "truecolor",
1302                                           "24bit"))
1303                                 cached_color_mode = COLOR_24BIT;
1304                         else
1305                                 cached_color_mode = COLOR_256;
1306                 }
1307         }
1308
1309         return cached_color_mode;
1310 }
1311
1312 bool dev_console_colors_enabled(void) {
1313         _cleanup_free_ char *s = NULL;
1314         ColorMode m;
1315
1316         /* Returns true if we assume that color is supported on /dev/console.
1317          *
1318          * For that we first check if we explicitly got told to use colors or not, by checking $SYSTEMD_COLORS. If that
1319          * isn't set we check whether PID 1 has $TERM set, and if not, whether TERM is set on the kernel command
1320          * line. If we find $TERM set we assume color if it's not set to "dumb", similarly to how regular
1321          * colors_enabled() operates. */
1322
1323         m = parse_systemd_colors();
1324         if (m >= 0)
1325                 return m;
1326
1327         if (getenv("NO_COLOR"))
1328                 return false;
1329
1330         if (getenv_for_pid(1, "TERM", &s) <= 0)
1331                 (void) proc_cmdline_get_key("TERM", 0, &s);
1332
1333         return !streq_ptr(s, "dumb");
1334 }
1335
1336 bool underline_enabled(void) {
1337
1338         if (cached_underline_enabled < 0) {
1339
1340                 /* The Linux console doesn't support underlining, turn it off, but only there. */
1341
1342                 if (colors_enabled())
1343                         cached_underline_enabled = !streq_ptr(getenv("TERM"), "linux");
1344                 else
1345                         cached_underline_enabled = false;
1346         }
1347
1348         return cached_underline_enabled;
1349 }
1350
1351 int vt_default_utf8(void) {
1352         _cleanup_free_ char *b = NULL;
1353         int r;
1354
1355         /* Read the default VT UTF8 setting from the kernel */
1356
1357         r = read_one_line_file("/sys/module/vt/parameters/default_utf8", &b);
1358         if (r < 0)
1359                 return r;
1360
1361         return parse_boolean(b);
1362 }
1363
1364 int vt_reset_keyboard(int fd) {
1365         int kb;
1366
1367         /* If we can't read the default, then default to unicode. It's 2017 after all. */
1368         kb = vt_default_utf8() != 0 ? K_UNICODE : K_XLATE;
1369
1370         return RET_NERRNO(ioctl(fd, KDSKBMODE, kb));
1371 }
1372
1373 int vt_restore(int fd) {
1374         static const struct vt_mode mode = {
1375                 .mode = VT_AUTO,
1376         };
1377         int r, q = 0;
1378
1379         if (isatty(fd) < 1)
1380                 return log_debug_errno(errno, "Asked to restore the VT for an fd that does not refer to a terminal: %m");
1381
1382         if (ioctl(fd, KDSETMODE, KD_TEXT) < 0)
1383                 q = log_debug_errno(errno, "Failed to set VT in text mode, ignoring: %m");
1384
1385         r = vt_reset_keyboard(fd);
1386         if (r < 0) {
1387                 log_debug_errno(r, "Failed to reset keyboard mode, ignoring: %m");
1388                 if (q >= 0)
1389                         q = r;
1390         }
1391
1392         if (ioctl(fd, VT_SETMODE, &mode) < 0) {
1393                 log_debug_errno(errno, "Failed to set VT_AUTO mode, ignoring: %m");
1394                 if (q >= 0)
1395                         q = -errno;
1396         }
1397
1398         r = fchmod_and_chown(fd, TTY_MODE, 0, GID_INVALID);
1399         if (r < 0) {
1400                 log_debug_errno(r, "Failed to chmod()/chown() VT, ignoring: %m");
1401                 if (q >= 0)
1402                         q = r;
1403         }
1404
1405         return q;
1406 }
1407
1408 int vt_release(int fd, bool restore) {
1409         assert(fd >= 0);
1410
1411         /* This function releases the VT by acknowledging the VT-switch signal
1412          * sent by the kernel and optionally reset the VT in text and auto
1413          * VT-switching modes. */
1414
1415         if (isatty(fd) < 1)
1416                 return log_debug_errno(errno, "Asked to release the VT for an fd that does not refer to a terminal: %m");
1417
1418         if (ioctl(fd, VT_RELDISP, 1) < 0)
1419                 return -errno;
1420
1421         if (restore)
1422                 return vt_restore(fd);
1423
1424         return 0;
1425 }
1426
1427 void get_log_colors(int priority, const char **on, const char **off, const char **highlight) {
1428         /* Note that this will initialize output variables only when there's something to output.
1429          * The caller must pre-initialize to "" or NULL as appropriate. */
1430
1431         if (priority <= LOG_ERR) {
1432                 if (on)
1433                         *on = ansi_highlight_red();
1434                 if (off)
1435                         *off = ansi_normal();
1436                 if (highlight)
1437                         *highlight = ansi_highlight();
1438
1439         } else if (priority <= LOG_WARNING) {
1440                 if (on)
1441                         *on = ansi_highlight_yellow();
1442                 if (off)
1443                         *off = ansi_normal();
1444                 if (highlight)
1445                         *highlight = ansi_highlight();
1446
1447         } else if (priority <= LOG_NOTICE) {
1448                 if (on)
1449                         *on = ansi_highlight();
1450                 if (off)
1451                         *off = ansi_normal();
1452                 if (highlight)
1453                         *highlight = ansi_highlight_red();
1454
1455         } else if (priority >= LOG_DEBUG) {
1456                 if (on)
1457                         *on = ansi_grey();
1458                 if (off)
1459                         *off = ansi_normal();
1460                 if (highlight)
1461                         *highlight = ansi_highlight_red();
1462         }
1463 }