man2/ioctl_tty.2

   1 .\" Copyright 2002 Walter Harms <walter.harms@informatik.uni-oldenburg.de>
   2 .\" and Andries Brouwer <aeb@cwi.nl>.
   3 .\"
   4 .\" SPDX-License-Identifier: GPL-1.0-or-later
   5 .\"
   6 .TH IOCTL_TTY 2 2021-08-27 "Linux" "Linux Programmer's Manual"
   7 .SH NAME
   8 ioctl_tty \- ioctls for terminals and serial lines
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc ", " \-lc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #include <sys/ioctl.h>
  15 .BR "#include <asm/termbits.h>" "   /* Definition of " "struct termios" ,
  16 .BR    "                               struct termios2" ", and"
  17 .BR    "                               Bnnn" ", " BOTHER ", " CBAUD ", " CLOCAL ,
  18 .BR    "                               TC*" { FLUSH , ON , OFF "} and other constants */"
  19 .PP
  20 .BI "int ioctl(int " fd ", int " cmd ", ...);"
  21 .fi
  22 .SH DESCRIPTION
  23 The
  24 .BR ioctl (2)
  25 call for terminals and serial ports accepts many possible command arguments.
  26 Most require a third argument, of varying type, here called
  27 .I argp
  28 or
  29 .IR arg .
  30 .PP
  31 Use of
  32 .BR ioctl ()
  33 makes for nonportable programs.
  34 Use the POSIX interface described in
  35 .BR termios (3)
  36 whenever possible.
  37 .PP
  38 Please note that
  39 .B struct termios
  40 from
  41 .I <asm/termbits.h>
  42 is different and incompatible with
  43 .B struct termios
  44 from
  45 .IR <termios.h> .
  46 These ioctl calls require
  47 .B struct termios
  48 from
  49 .IR <asm/termbits.h> .
  50 .SS Get and set terminal attributes
  51 .TP
  52 .B TCGETS
  53 Argument:
  54 .BI "struct termios\~*" argp
  55 .IP
  56 Equivalent to
  57 .IR "tcgetattr(fd, argp)" .
  58 .IP
  59 Get the current serial port settings.
  60 .TP
  61 .B TCSETS
  62 Argument:
  63 .BI "const struct termios\~*" argp
  64 .IP
  65 Equivalent to
  66 .IR "tcsetattr(fd, TCSANOW, argp)" .
  67 .IP
  68 Set the current serial port settings.
  69 .TP
  70 .B TCSETSW
  71 Argument:
  72 .BI "const struct termios\~*" argp
  73 .IP
  74 Equivalent to
  75 .IR "tcsetattr(fd, TCSADRAIN, argp)" .
  76 .IP
  77 Allow the output buffer to drain, and
  78 set the current serial port settings.
  79 .TP
  80 .B TCSETSF
  81 Argument:
  82 .BI "const struct termios\~*" argp
  83 .IP
  84 Equivalent to
  85 .IR "tcsetattr(fd, TCSAFLUSH, argp)" .
  86 .IP
  87 Allow the output buffer to drain, discard pending input, and
  88 set the current serial port settings.
  89 .PP
  90 The following four ioctls, added in Linux 2.6.20,
  91 .\" commit 64bb6c5e1ddcd47c951740485026ef08975ee2e6
  92 .\" commit 592ee3a5e5e2a981ef2829a0380093006d045661
  93 are just like
  94 .BR TCGETS ,
  95 .BR TCSETS ,
  96 .BR TCSETSW ,
  97 .BR TCSETSF ,
  98 except that they take a
  99 .I "struct termios2\~*"
 100 instead of a
 101 .IR "struct termios\~*" .
 102 If the structure member
 103 .B c_cflag
 104 contains the flag
 105 .BR BOTHER ,
 106 then the baud rate is stored in the structure members
 107 .B c_ispeed
 108 and
 109 .B c_ospeed
 110 as integer values.
 111 These ioctls are not supported on all architectures.
 112 .RS
 113 .TS
 114 lb l.
 115 TCGETS2 \fBstruct termios2 *\fPargp
 116 TCSETS2 \fBconst struct termios2 *\fPargp
 117 TCSETSW2        \fBconst struct termios2 *\fPargp
 118 TCSETSF2        \fBconst struct termios2 *\fPargp
 119 .TE
 120 .RE
 121 .PP
 122 The following four ioctls are just like
 123 .BR TCGETS ,
 124 .BR TCSETS ,
 125 .BR TCSETSW ,
 126 .BR TCSETSF ,
 127 except that they take a
 128 .I "struct termio\~*"
 129 instead of a
 130 .IR "struct termios\~*" .
 131 .RS
 132 .TS
 133 lb l.
 134 TCGETA  \fBstruct termio *\fPargp
 135 TCSETA  \fBconst struct termio *\fPargp
 136 TCSETAW \fBconst struct termio *\fPargp
 137 TCSETAF \fBconst struct termio *\fPargp
 138 .TE
 139 .RE
 140 .SS Locking the termios structure
 141 The
 142 .I termios
 143 structure of a terminal can be locked.
 144 The lock is itself a
 145 .I termios
 146 structure, with nonzero bits or fields indicating a
 147 locked value.
 148 .TP
 149 .B TIOCGLCKTRMIOS
 150 Argument:
 151 .BI "struct termios\~*" argp
 152 .IP
 153 Gets the locking status of the
 154 .I termios
 155 structure of the terminal.
 156 .TP
 157 .B TIOCSLCKTRMIOS
 158 Argument:
 159 .BI "const struct termios\~*" argp
 160 .IP
 161 Sets the locking status of the
 162 .I termios
 163 structure of the terminal.
 164 Only a process with the
 165 .B CAP_SYS_ADMIN
 166 capability can do this.
 167 .SS Get and set window size
 168 Window sizes are kept in the kernel, but not used by the kernel
 169 (except in the case of virtual consoles, where the kernel will
 170 update the window size when the size of the virtual console changes,
 171 for example, by loading a new font).
 172 .TP
 173 .B TIOCGWINSZ
 174 Argument:
 175 .BI "struct winsize\~*" argp
 176 .IP
 177 Get window size.
 178 .TP
 179 .B TIOCSWINSZ
 180 Argument:
 181 .BI "const struct winsize\~*" argp
 182 .IP
 183 Set window size.
 184 .PP
 185 The struct used by these ioctls is defined as
 186 .PP
 187 .in +4n
 188 .EX
 189 struct winsize {
 190     unsigned short ws_row;
 191     unsigned short ws_col;
 192     unsigned short ws_xpixel;   /* unused */
 193     unsigned short ws_ypixel;   /* unused */
 194 };
 195 .EE
 196 .in
 197 .PP
 198 When the window size changes, a
 199 .B SIGWINCH
 200 signal is sent to the
 201 foreground process group.
 202 .SS Sending a break
 203 .TP
 204 .B TCSBRK
 205 Argument:
 206 .BI "int " arg
 207 .IP
 208 Equivalent to
 209 .IR "tcsendbreak(fd, arg)" .
 210 .IP
 211 If the terminal is using asynchronous serial data transmission, and
 212 .I arg
 213 is zero, then send a break (a stream of zero bits) for between
 214 0.25 and 0.5 seconds.
 215 If the terminal is not using asynchronous
 216 serial data transmission, then either a break is sent, or the function
 217 returns without doing anything.
 218 When
 219 .I arg
 220 is nonzero, nobody knows what will happen.
 221 .IP
 222 (SVr4, UnixWare, Solaris, and Linux treat
 223 .I "tcsendbreak(fd,arg)"
 224 with nonzero
 225 .I arg
 226 like
 227 .IR "tcdrain(fd)" .
 228 SunOS treats
 229 .I arg
 230 as a multiplier, and sends a stream of bits
 231 .I arg
 232 times as long as done for zero
 233 .IR arg .
 234 DG/UX and AIX treat
 235 .I arg
 236 (when nonzero) as a time interval measured in milliseconds.
 237 HP-UX ignores
 238 .IR arg .)
 239 .TP
 240 .B TCSBRKP
 241 Argument:
 242 .BI "int " arg
 243 .IP
 244 So-called "POSIX version" of
 245 .BR TCSBRK .
 246 It treats nonzero
 247 .I arg
 248 as a time interval measured in deciseconds, and does nothing
 249 when the driver does not support breaks.
 250 .TP
 251 .B TIOCSBRK
 252 Argument:
 253 .B void
 254 .IP
 255 Turn break on, that is, start sending zero bits.
 256 .TP
 257 .B TIOCCBRK
 258 Argument:
 259 .B void
 260 .IP
 261 Turn break off, that is, stop sending zero bits.
 262 .SS Software flow control
 263 .TP
 264 .B TCXONC
 265 Argument:
 266 .BI "int " arg
 267 .IP
 268 Equivalent to
 269 .IR "tcflow(fd, arg)" .
 270 .IP
 271 See
 272 .BR tcflow (3)
 273 for the argument values
 274 .BR TCOOFF ,
 275 .BR TCOON ,
 276 .BR TCIOFF ,
 277 .BR TCION .
 278 .SS Buffer count and flushing
 279 .TP
 280 .B FIONREAD
 281 Argument:
 282 .BI "int\~*" argp
 283 .IP
 284 Get the number of bytes in the input buffer.
 285 .TP
 286 .B TIOCINQ
 287 Argument:
 288 .BI "int\~*" argp
 289 .IP
 290 Same as
 291 .BR FIONREAD .
 292 .TP
 293 .B TIOCOUTQ
 294 Argument:
 295 .BI "int\~*" argp
 296 .IP
 297 Get the number of bytes in the output buffer.
 298 .TP
 299 .B TCFLSH
 300 Argument:
 301 .BI "int " arg
 302 .IP
 303 Equivalent to
 304 .IR "tcflush(fd, arg)" .
 305 .IP
 306 See
 307 .BR tcflush (3)
 308 for the argument values
 309 .BR TCIFLUSH ,
 310 .BR TCOFLUSH ,
 311 .BR TCIOFLUSH .
 312 .SS Faking input
 313 .TP
 314 .B TIOCSTI
 315 Argument:
 316 .BI "const char\~*" argp
 317 .IP
 318 Insert the given byte in the input queue.
 319 .SS Redirecting console output
 320 .TP
 321 .B TIOCCONS
 322 Argument:
 323 .B void
 324 .IP
 325 Redirect output that would have gone to
 326 .I /dev/console
 327 or
 328 .I /dev/tty0
 329 to the given terminal.
 330 If that was a pseudoterminal master, send it to the slave.
 331 In Linux before version 2.6.10,
 332 anybody can do this as long as the output was not redirected yet;
 333 since version 2.6.10, only a process with the
 334 .B CAP_SYS_ADMIN
 335 capability may do this.
 336 If output was redirected already, then
 337 .B EBUSY
 338 is returned,
 339 but redirection can be stopped by using this ioctl with
 340 .I fd
 341 pointing at
 342 .I /dev/console
 343 or
 344 .IR /dev/tty0 .
 345 .SS Controlling terminal
 346 .TP
 347 .B TIOCSCTTY
 348 Argument:
 349 .BI "int " arg
 350 .IP
 351 Make the given terminal the controlling terminal of the calling process.
 352 The calling process must be a session leader and not have a
 353 controlling terminal already.
 354 For this case,
 355 .I arg
 356 should be specified as zero.
 357 .IP
 358 If this terminal is already the controlling terminal
 359 of a different session group, then the ioctl fails with
 360 .BR EPERM ,
 361 unless the caller has the
 362 .B CAP_SYS_ADMIN
 363 capability and
 364 .I arg
 365 equals 1, in which case the terminal is stolen, and all processes that had
 366 it as controlling terminal lose it.
 367 .TP
 368 .B TIOCNOTTY
 369 Argument:
 370 .B void
 371 .IP
 372 If the given terminal was the controlling terminal of the calling process,
 373 give up this controlling terminal.
 374 If the process was session leader,
 375 then send
 376 .B SIGHUP
 377 and
 378 .B SIGCONT
 379 to the foreground process group
 380 and all processes in the current session lose their controlling terminal.
 381 .SS Process group and session ID
 382 .TP
 383 .B TIOCGPGRP
 384 Argument:
 385 .BI "pid_t\~*" argp
 386 .IP
 387 When successful, equivalent to
 388 .IR "*argp = tcgetpgrp(fd)" .
 389 .IP
 390 Get the process group ID of the foreground process group on this terminal.
 391 .TP
 392 .B TIOCSPGRP
 393 Argument:
 394 .BI "const pid_t\~*" argp
 395 .IP
 396 Equivalent to
 397 .IR "tcsetpgrp(fd, *argp)" .
 398 .IP
 399 Set the foreground process group ID of this terminal.
 400 .TP
 401 .B TIOCGSID
 402 Argument:
 403 .BI "pid_t\~*" argp
 404 .IP
 405 When successful, equivalent to
 406 .IR "*argp = tcgetsid(fd)" .
 407 .IP
 408 Get the session ID of the given terminal.
 409 This fails with the error
 410 .B ENOTTY
 411 if the terminal is not a master pseudoterminal
 412 and not our controlling terminal.
 413 Strange.
 414 .SS Exclusive mode
 415 .TP
 416 .B TIOCEXCL
 417 Argument:
 418 .B void
 419 .IP
 420 Put the terminal into exclusive mode.
 421 No further
 422 .BR open (2)
 423 operations on the terminal are permitted.
 424 (They fail with
 425 .BR EBUSY ,
 426 except for a process with the
 427 .B CAP_SYS_ADMIN
 428 capability.)
 429 .TP
 430 .B TIOCGEXCL
 431 Argument:
 432 .BI "int\~*" argp
 433 .IP
 434 (since Linux 3.8)
 435 If the terminal is currently in exclusive mode,
 436 place a nonzero value in the location pointed to by
 437 .IR argp ;
 438 otherwise, place zero in
 439 .IR *argp .
 440 .TP
 441 .B TIOCNXCL
 442 Argument:
 443 .B void
 444 .IP
 445 Disable exclusive mode.
 446 .SS Line discipline
 447 .TP
 448 .B TIOCGETD
 449 Argument:
 450 .BI "int\~*" argp
 451 .IP
 452 Get the line discipline of the terminal.
 453 .TP
 454 .B TIOCSETD
 455 Argument:
 456 .BI "const int\~*" argp
 457 .IP
 458 Set the line discipline of the terminal.
 459 .SS Pseudoterminal ioctls
 460 .TP
 461 .B TIOCPKT
 462 Argument:
 463 .BI "const int\~*" argp
 464 .IP
 465 Enable (when
 466 .RI * argp
 467 is nonzero) or disable packet mode.
 468 Can be applied to the master side of a pseudoterminal only (and will return
 469 .B ENOTTY
 470 otherwise).
 471 In packet mode, each subsequent
 472 .BR read (2)
 473 will return a packet that either contains a single nonzero control byte,
 474 or has a single byte containing zero (\(aq\e0\(aq) followed by data
 475 written on the slave side of the pseudoterminal.
 476 If the first byte is not
 477 .B TIOCPKT_DATA
 478 (0), it is an OR of one
 479 or more of the following bits:
 480 .IP
 481 .ad l
 482 .TS
 483 lb l.
 484 TIOCPKT_FLUSHREAD       T{
 485 The read queue for the terminal is flushed.
 486 T}
 487 TIOCPKT_FLUSHWRITE      T{
 488 The write queue for the terminal is flushed.
 489 T}
 490 TIOCPKT_STOP    T{
 491 Output to the terminal is stopped.
 492 T}
 493 TIOCPKT_START   T{
 494 Output to the terminal is restarted.
 495 T}
 496 TIOCPKT_DOSTOP  T{
 497 The start and stop characters are \fB\(haS\fP/\fB\(haQ\fP.
 498 T}
 499 TIOCPKT_NOSTOP  T{
 500 The start and stop characters are not \fB\(haS\fP/\fB\(haQ\fP.
 501 T}
 502 .TE
 503 .ad
 504 .IP
 505 While packet mode is in use, the presence
 506 of control status information to be read
 507 from the master side may be detected by a
 508 .BR select (2)
 509 for exceptional conditions or a
 510 .BR poll (2)
 511 for the
 512 .B POLLPRI
 513 event.
 514 .IP
 515 This mode is used by
 516 .BR rlogin (1)
 517 and
 518 .BR rlogind (8)
 519 to implement a remote-echoed,
 520 locally \fB\(haS\fP/\fB\(haQ\fP flow-controlled remote login.
 521 .TP
 522 .B TIOCGPKT
 523 Argument:
 524 .BI "const int\~*" argp
 525 .IP
 526 (since Linux 3.8)
 527 Return the current packet mode setting in the integer pointed to by
 528 .IR argp .
 529 .TP
 530 .B TIOCSPTLCK
 531 Argument:
 532 .BI "int\~*" argp
 533 .IP
 534 Set (if
 535 .I *argp
 536 is nonzero) or remove (if
 537 .I *argp
 538 is zero) the lock on the pseudoterminal slave device.
 539 (See also
 540 .BR unlockpt (3).)
 541 .TP
 542 .B TIOCGPTLCK
 543 Argument:
 544 .BI "int\~*" argp
 545 .IP
 546 (since Linux 3.8)
 547 Place the current lock state of the pseudoterminal slave device
 548 in the location pointed to by
 549 .IR argp .
 550 .TP
 551 .B TIOCGPTPEER
 552 Argument:
 553 .BI "int " flags
 554 .IP
 555 .\" commit 54ebbfb1603415d9953c150535850d30609ef077
 556 (since Linux 4.13)
 557 Given a file descriptor in
 558 .I fd
 559 that refers to a pseudoterminal master,
 560 open (with the given
 561 .BR open (2)-style
 562 .IR flags )
 563 and return a new file descriptor that refers to the peer
 564 pseudoterminal slave device.
 565 This operation can be performed
 566 regardless of whether the pathname of the slave device
 567 is accessible through the calling process's mount namespace.
 568 .IP
 569 Security-conscious programs interacting with namespaces may wish to use this
 570 operation rather than
 571 .BR open (2)
 572 with the pathname returned by
 573 .BR ptsname (3),
 574 and similar library functions that have insecure APIs.
 575 (For example, confusion can occur in some cases using
 576 .BR ptsname (3)
 577 with a pathname where a devpts filesystem
 578 has been mounted in a different mount namespace.)
 579 .PP
 580 The BSD ioctls
 581 .BR TIOCSTOP ,
 582 .BR TIOCSTART ,
 583 .BR TIOCUCNTL ,
 584 and
 585 .B TIOCREMOTE
 586 have not been implemented under Linux.
 587 .SS Modem control
 588 .TP
 589 .B TIOCMGET
 590 Argument:
 591 .BI "int\~*" argp
 592 .IP
 593 Get the status of modem bits.
 594 .TP
 595 .B TIOCMSET
 596 Argument:
 597 .BI "const int\~*" argp
 598 .IP
 599 Set the status of modem bits.
 600 .TP
 601 .B TIOCMBIC
 602 Argument:
 603 .BI "const int\~*" argp
 604 .IP
 605 Clear the indicated modem bits.
 606 .TP
 607 .B TIOCMBIS
 608 Argument:
 609 .BI "const int\~*" argp
 610 .IP
 611 Set the indicated modem bits.
 612 .PP
 613 The following bits are used by the above ioctls:
 614 .PP
 615 .TS
 616 lb l.
 617 TIOCM_LE        DSR (data set ready/line enable)
 618 TIOCM_DTR       DTR (data terminal ready)
 619 TIOCM_RTS       RTS (request to send)
 620 TIOCM_ST        Secondary TXD (transmit)
 621 TIOCM_SR        Secondary RXD (receive)
 622 TIOCM_CTS       CTS (clear to send)
 623 TIOCM_CAR       DCD (data carrier detect)
 624 TIOCM_CD        see TIOCM_CAR
 625 TIOCM_RNG       RNG (ring)
 626 TIOCM_RI        see TIOCM_RNG
 627 TIOCM_DSR       DSR (data set ready)
 628 .TE
 629 .TP
 630 .B TIOCMIWAIT
 631 Argument:
 632 .BI "int " arg
 633 .IP
 634 Wait for any of the 4 modem bits (DCD, RI, DSR, CTS) to change.
 635 The bits of interest are specified as a bit mask in
 636 .IR arg ,
 637 by ORing together any of the bit values,
 638 .BR TIOCM_RNG ,
 639 .BR TIOCM_DSR ,
 640 .BR TIOCM_CD ,
 641 and
 642 .BR TIOCM_CTS .
 643 The caller should use
 644 .B TIOCGICOUNT
 645 to see which bit has changed.
 646 .TP
 647 .B TIOCGICOUNT
 648 Argument:
 649 .BI "struct serial_icounter_struct\~*" argp
 650 .IP
 651 Get counts of input serial line interrupts (DCD, RI, DSR, CTS).
 652 The counts are written to the
 653 .I serial_icounter_struct
 654 structure pointed to by
 655 .IR argp .
 656 .IP
 657 Note: both 1->0 and 0->1 transitions are counted, except for
 658 RI, where only 0->1 transitions are counted.
 659 .SS Marking a line as local
 660 .TP
 661 .B TIOCGSOFTCAR
 662 Argument:
 663 .BI "int\~*" argp
 664 .IP
 665 ("Get software carrier flag")
 666 Get the status of the CLOCAL flag in the c_cflag field of the
 667 .I termios
 668 structure.
 669 .TP
 670 .B TIOCSSOFTCAR
 671 Argument:
 672 .BI "const int\~*" argp
 673 .IP
 674 ("Set software carrier flag")
 675 Set the CLOCAL flag in the
 676 .I termios
 677 structure when
 678 .RI * argp
 679 is nonzero, and clear it otherwise.
 680 .PP
 681 If the
 682 .B CLOCAL
 683 flag for a line is off, the hardware carrier detect (DCD)
 684 signal is significant, and an
 685 .BR open (2)
 686 of the corresponding terminal will block until DCD is asserted,
 687 unless the
 688 .B O_NONBLOCK
 689 flag is given.
 690 If
 691 .B CLOCAL
 692 is set, the line behaves as if DCD is always asserted.
 693 The software carrier flag is usually turned on for local devices,
 694 and is off for lines with modems.
 695 .SS Linux-specific
 696 For the
 697 .B TIOCLINUX
 698 ioctl, see
 699 .BR ioctl_console (2).
 700 .SS Kernel debugging
 701 .B "#include <linux/tty.h>"
 702 .TP
 703 .B TIOCTTYGSTRUCT
 704 Argument:
 705 .BI "struct tty_struct\~*" argp
 706 .IP
 707 Get the
 708 .I tty_struct
 709 corresponding to
 710 .IR fd .
 711 This command was removed in Linux 2.5.67.
 712 .\"     commit b3506a09d15dc5aee6d4bb88d759b157016e1864
 713 .\"     Author: Andries E. Brouwer <andries.brouwer@cwi.nl>
 714 .\"     Date:   Tue Apr 1 04:42:46 2003 -0800
 715 .\"
 716 .\"     [PATCH] kill TIOCTTYGSTRUCT
 717 .\"
 718 .\"     Only used for (dubious) debugging purposes, and exposes
 719 .\"     internal kernel state.
 720 .\"
 721 .\" .SS Serial info
 722 .\" .BR "#include <linux/serial.h>"
 723 .\" .PP
 724 .\" .TP
 725 .\" .BI "TIOCGSERIAL    struct serial_struct *" argp
 726 .\" Get serial info.
 727 .\" .TP
 728 .\" .BI "TIOCSSERIAL    const struct serial_struct *" argp
 729 .\" Set serial info.
 730 .SH RETURN VALUE
 731 The
 732 .BR ioctl (2)
 733 system call returns 0 on success.
 734 On error, it returns \-1 and sets
 735 .I errno
 736 to indicate the error.
 737 .SH ERRORS
 738 .TP
 739 .B EINVAL
 740 Invalid command parameter.
 741 .TP
 742 .B ENOIOCTLCMD
 743 Unknown command.
 744 .TP
 745 .B ENOTTY
 746 Inappropriate
 747 .IR fd .
 748 .TP
 749 .B EPERM
 750 Insufficient permission.
 751 .SH EXAMPLES
 752 Check the condition of DTR on the serial port.
 753 .PP
 754 .\" SRC BEGIN (tiocmget.c)
 755 .EX
 756 #include <fcntl.h>
 757 #include <stdio.h>
 758 #include <sys/ioctl.h>
 759 #include <unistd.h>
 760
 761 int
 762 main(void)
 763 {
 764     int fd, serial;
 765
 766     fd = open("/dev/ttyS0", O_RDONLY);
 767     ioctl(fd, TIOCMGET, &serial);
 768     if (serial & TIOCM_DTR)
 769         puts("TIOCM_DTR is set");
 770     else
 771         puts("TIOCM_DTR is not set");
 772     close(fd);
 773 }
 774 .EE
 775 .\" SRC END
 776 .PP
 777 Get or set arbitrary baudrate on the serial port.
 778 .PP
 779 .\" SRC BEGIN (tcgets.c)
 780 .EX
 781 /* SPDX-License-Identifier: GPL-2.0-or-later */
 782
 783 #include <asm/termbits.h>
 784 #include <fcntl.h>
 785 #include <stdio.h>
 786 #include <stdlib.h>
 787 #include <sys/ioctl.h>
 788 #include <sys/types.h>
 789 #include <unistd.h>
 790
 791 int
 792 main(int argc, char *argv[])
 793 {
 794 #if !defined BOTHER
 795     fprintf(stderr, "BOTHER is unsupported\en");
 796     /* Program may fallback to TCGETS/TCSETS with Bnnn constants */
 797     exit(EXIT_FAILURE);
 798 #else
 799     /* Declare tio structure, its type depends on supported ioctl */
 800 # if defined TCGETS2
 801     struct termios2 tio;
 802 # else
 803     struct termios tio;
 804 # endif
 805     int fd, rc;
 806
 807     if (argc != 2 && argc != 3 && argc != 4) {
 808         fprintf(stderr, "Usage: %s device [output [input] ]\en", argv[0]);
 809         exit(EXIT_FAILURE);
 810     }
 811
 812     fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
 813     if (fd < 0) {
 814         perror("open");
 815         exit(EXIT_FAILURE);
 816     }
 817
 818     /* Get the current serial port settings via supported ioctl */
 819 # if defined TCGETS2
 820     rc = ioctl(fd, TCGETS2, &tio);
 821 # else
 822     rc = ioctl(fd, TCGETS, &tio);
 823 # endif
 824     if (rc) {
 825         perror("TCGETS");
 826         close(fd);
 827         exit(EXIT_FAILURE);
 828     }
 829
 830     /* Change baud rate when more arguments were provided */
 831     if (argc == 3 || argc == 4) {
 832         /* Clear the current output baud rate and fill a new value */
 833         tio.c_cflag &= ~CBAUD;
 834         tio.c_cflag |= BOTHER;
 835         tio.c_ospeed = atoi(argv[2]);
 836
 837         /* Clear the current input baud rate and fill a new value */
 838         tio.c_cflag &= ~(CBAUD << IBSHIFT);
 839         tio.c_cflag |= BOTHER << IBSHIFT;
 840         /* When 4th argument is not provided reuse output baud rate */
 841         tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);
 842
 843         /* Set new serial port settings via supported ioctl */
 844 # if defined TCSETS2
 845         rc = ioctl(fd, TCSETS2, &tio);
 846 # else
 847         rc = ioctl(fd, TCSETS, &tio);
 848 # endif
 849         if (rc) {
 850             perror("TCSETS");
 851             close(fd);
 852             exit(EXIT_FAILURE);
 853         }
 854
 855         /* And get new values which were really configured */
 856 # if defined TCGETS2
 857         rc = ioctl(fd, TCGETS2, &tio);
 858 # else
 859         rc = ioctl(fd, TCGETS, &tio);
 860 # endif
 861         if (rc) {
 862             perror("TCGETS");
 863             close(fd);
 864             exit(EXIT_FAILURE);
 865         }
 866     }
 867
 868     close(fd);
 869
 870     printf("output baud rate: %u\en", tio.c_ospeed);
 871     printf("input baud rate: %u\en", tio.c_ispeed);
 872
 873     exit(EXIT_SUCCESS);
 874 #endif
 875 }
 876 .EE
 877 .\" SRC END
 878 .SH SEE ALSO
 879 .BR ldattach (8),
 880 .BR ioctl (2),
 881 .BR ioctl_console (2),
 882 .BR termios (3),
 883 .BR pty (7)
 884 .\"
 885 .\" FIONBIO                     const int *
 886 .\" FIONCLEX                    void
 887 .\" FIOCLEX                     void
 888 .\" FIOASYNC                    const int *
 889 .\" from serial.c:
 890 .\" TIOCSERCONFIG               void
 891 .\" TIOCSERGWILD                int *
 892 .\" TIOCSERSWILD                const int *
 893 .\" TIOCSERGSTRUCT              struct async_struct *
 894 .\" TIOCSERGETLSR               int *
 895 .\" TIOCSERGETMULTI             struct serial_multiport_struct *
 896 .\" TIOCSERSETMULTI             const struct serial_multiport_struct *
 897 .\" TIOCGSERIAL, TIOCSSERIAL (see above)