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 (date) "Linux man-pages (unreleased)"
   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 .TP
 313 .B TIOCSERGETLSR
 314 Argument:
 315 .BI "int\~*" argp
 316 .IP
 317 Get line status register. Status register has
 318 .B TIOCSER_TEMT
 319 bit set when output buffer is empty and also hardware transmitter is physically empty.
 320 .IP
 321 Does not have to be supported by all serial tty drivers.
 322 .IP
 323 .BR tcdrain (3)
 324 does not wait and returns immediately when
 325 .B TIOCSER_TEMT
 326 bit is set.
 327 .SS Faking input
 328 .TP
 329 .B TIOCSTI
 330 Argument:
 331 .BI "const char\~*" argp
 332 .IP
 333 Insert the given byte in the input queue.
 334 .SS Redirecting console output
 335 .TP
 336 .B TIOCCONS
 337 Argument:
 338 .B void
 339 .IP
 340 Redirect output that would have gone to
 341 .I /dev/console
 342 or
 343 .I /dev/tty0
 344 to the given terminal.
 345 If that was a pseudoterminal master, send it to the slave.
 346 In Linux before version 2.6.10,
 347 anybody can do this as long as the output was not redirected yet;
 348 since version 2.6.10, only a process with the
 349 .B CAP_SYS_ADMIN
 350 capability may do this.
 351 If output was redirected already, then
 352 .B EBUSY
 353 is returned,
 354 but redirection can be stopped by using this ioctl with
 355 .I fd
 356 pointing at
 357 .I /dev/console
 358 or
 359 .IR /dev/tty0 .
 360 .SS Controlling terminal
 361 .TP
 362 .B TIOCSCTTY
 363 Argument:
 364 .BI "int " arg
 365 .IP
 366 Make the given terminal the controlling terminal of the calling process.
 367 The calling process must be a session leader and not have a
 368 controlling terminal already.
 369 For this case,
 370 .I arg
 371 should be specified as zero.
 372 .IP
 373 If this terminal is already the controlling terminal
 374 of a different session group, then the ioctl fails with
 375 .BR EPERM ,
 376 unless the caller has the
 377 .B CAP_SYS_ADMIN
 378 capability and
 379 .I arg
 380 equals 1, in which case the terminal is stolen, and all processes that had
 381 it as controlling terminal lose it.
 382 .TP
 383 .B TIOCNOTTY
 384 Argument:
 385 .B void
 386 .IP
 387 If the given terminal was the controlling terminal of the calling process,
 388 give up this controlling terminal.
 389 If the process was session leader,
 390 then send
 391 .B SIGHUP
 392 and
 393 .B SIGCONT
 394 to the foreground process group
 395 and all processes in the current session lose their controlling terminal.
 396 .SS Process group and session ID
 397 .TP
 398 .B TIOCGPGRP
 399 Argument:
 400 .BI "pid_t\~*" argp
 401 .IP
 402 When successful, equivalent to
 403 .IR "*argp = tcgetpgrp(fd)" .
 404 .IP
 405 Get the process group ID of the foreground process group on this terminal.
 406 .TP
 407 .B TIOCSPGRP
 408 Argument:
 409 .BI "const pid_t\~*" argp
 410 .IP
 411 Equivalent to
 412 .IR "tcsetpgrp(fd, *argp)" .
 413 .IP
 414 Set the foreground process group ID of this terminal.
 415 .TP
 416 .B TIOCGSID
 417 Argument:
 418 .BI "pid_t\~*" argp
 419 .IP
 420 When successful, equivalent to
 421 .IR "*argp = tcgetsid(fd)" .
 422 .IP
 423 Get the session ID of the given terminal.
 424 This fails with the error
 425 .B ENOTTY
 426 if the terminal is not a master pseudoterminal
 427 and not our controlling terminal.
 428 Strange.
 429 .SS Exclusive mode
 430 .TP
 431 .B TIOCEXCL
 432 Argument:
 433 .B void
 434 .IP
 435 Put the terminal into exclusive mode.
 436 No further
 437 .BR open (2)
 438 operations on the terminal are permitted.
 439 (They fail with
 440 .BR EBUSY ,
 441 except for a process with the
 442 .B CAP_SYS_ADMIN
 443 capability.)
 444 .TP
 445 .B TIOCGEXCL
 446 Argument:
 447 .BI "int\~*" argp
 448 .IP
 449 (since Linux 3.8)
 450 If the terminal is currently in exclusive mode,
 451 place a nonzero value in the location pointed to by
 452 .IR argp ;
 453 otherwise, place zero in
 454 .IR *argp .
 455 .TP
 456 .B TIOCNXCL
 457 Argument:
 458 .B void
 459 .IP
 460 Disable exclusive mode.
 461 .SS Line discipline
 462 .TP
 463 .B TIOCGETD
 464 Argument:
 465 .BI "int\~*" argp
 466 .IP
 467 Get the line discipline of the terminal.
 468 .TP
 469 .B TIOCSETD
 470 Argument:
 471 .BI "const int\~*" argp
 472 .IP
 473 Set the line discipline of the terminal.
 474 .SS Pseudoterminal ioctls
 475 .TP
 476 .B TIOCPKT
 477 Argument:
 478 .BI "const int\~*" argp
 479 .IP
 480 Enable (when
 481 .RI * argp
 482 is nonzero) or disable packet mode.
 483 Can be applied to the master side of a pseudoterminal only (and will return
 484 .B ENOTTY
 485 otherwise).
 486 In packet mode, each subsequent
 487 .BR read (2)
 488 will return a packet that either contains a single nonzero control byte,
 489 or has a single byte containing zero (\(aq\e0\(aq) followed by data
 490 written on the slave side of the pseudoterminal.
 491 If the first byte is not
 492 .B TIOCPKT_DATA
 493 (0), it is an OR of one
 494 or more of the following bits:
 495 .IP
 496 .ad l
 497 .TS
 498 lb l.
 499 TIOCPKT_FLUSHREAD       T{
 500 The read queue for the terminal is flushed.
 501 T}
 502 TIOCPKT_FLUSHWRITE      T{
 503 The write queue for the terminal is flushed.
 504 T}
 505 TIOCPKT_STOP    T{
 506 Output to the terminal is stopped.
 507 T}
 508 TIOCPKT_START   T{
 509 Output to the terminal is restarted.
 510 T}
 511 TIOCPKT_DOSTOP  T{
 512 The start and stop characters are \fB\(haS\fP/\fB\(haQ\fP.
 513 T}
 514 TIOCPKT_NOSTOP  T{
 515 The start and stop characters are not \fB\(haS\fP/\fB\(haQ\fP.
 516 T}
 517 .TE
 518 .ad
 519 .IP
 520 While packet mode is in use, the presence
 521 of control status information to be read
 522 from the master side may be detected by a
 523 .BR select (2)
 524 for exceptional conditions or a
 525 .BR poll (2)
 526 for the
 527 .B POLLPRI
 528 event.
 529 .IP
 530 This mode is used by
 531 .BR rlogin (1)
 532 and
 533 .BR rlogind (8)
 534 to implement a remote-echoed,
 535 locally \fB\(haS\fP/\fB\(haQ\fP flow-controlled remote login.
 536 .TP
 537 .B TIOCGPKT
 538 Argument:
 539 .BI "const int\~*" argp
 540 .IP
 541 (since Linux 3.8)
 542 Return the current packet mode setting in the integer pointed to by
 543 .IR argp .
 544 .TP
 545 .B TIOCSPTLCK
 546 Argument:
 547 .BI "int\~*" argp
 548 .IP
 549 Set (if
 550 .I *argp
 551 is nonzero) or remove (if
 552 .I *argp
 553 is zero) the lock on the pseudoterminal slave device.
 554 (See also
 555 .BR unlockpt (3).)
 556 .TP
 557 .B TIOCGPTLCK
 558 Argument:
 559 .BI "int\~*" argp
 560 .IP
 561 (since Linux 3.8)
 562 Place the current lock state of the pseudoterminal slave device
 563 in the location pointed to by
 564 .IR argp .
 565 .TP
 566 .B TIOCGPTPEER
 567 Argument:
 568 .BI "int " flags
 569 .IP
 570 .\" commit 54ebbfb1603415d9953c150535850d30609ef077
 571 (since Linux 4.13)
 572 Given a file descriptor in
 573 .I fd
 574 that refers to a pseudoterminal master,
 575 open (with the given
 576 .BR open (2)-style
 577 .IR flags )
 578 and return a new file descriptor that refers to the peer
 579 pseudoterminal slave device.
 580 This operation can be performed
 581 regardless of whether the pathname of the slave device
 582 is accessible through the calling process's mount namespace.
 583 .IP
 584 Security-conscious programs interacting with namespaces may wish to use this
 585 operation rather than
 586 .BR open (2)
 587 with the pathname returned by
 588 .BR ptsname (3),
 589 and similar library functions that have insecure APIs.
 590 (For example, confusion can occur in some cases using
 591 .BR ptsname (3)
 592 with a pathname where a devpts filesystem
 593 has been mounted in a different mount namespace.)
 594 .PP
 595 The BSD ioctls
 596 .BR TIOCSTOP ,
 597 .BR TIOCSTART ,
 598 .BR TIOCUCNTL ,
 599 and
 600 .B TIOCREMOTE
 601 have not been implemented under Linux.
 602 .SS Modem control
 603 .TP
 604 .B TIOCMGET
 605 Argument:
 606 .BI "int\~*" argp
 607 .IP
 608 Get the status of modem bits.
 609 .TP
 610 .B TIOCMSET
 611 Argument:
 612 .BI "const int\~*" argp
 613 .IP
 614 Set the status of modem bits.
 615 .TP
 616 .B TIOCMBIC
 617 Argument:
 618 .BI "const int\~*" argp
 619 .IP
 620 Clear the indicated modem bits.
 621 .TP
 622 .B TIOCMBIS
 623 Argument:
 624 .BI "const int\~*" argp
 625 .IP
 626 Set the indicated modem bits.
 627 .PP
 628 The following bits are used by the above ioctls:
 629 .PP
 630 .TS
 631 lb l.
 632 TIOCM_LE        DSR (data set ready/line enable)
 633 TIOCM_DTR       DTR (data terminal ready)
 634 TIOCM_RTS       RTS (request to send)
 635 TIOCM_ST        Secondary TXD (transmit)
 636 TIOCM_SR        Secondary RXD (receive)
 637 TIOCM_CTS       CTS (clear to send)
 638 TIOCM_CAR       DCD (data carrier detect)
 639 TIOCM_CD        see TIOCM_CAR
 640 TIOCM_RNG       RNG (ring)
 641 TIOCM_RI        see TIOCM_RNG
 642 TIOCM_DSR       DSR (data set ready)
 643 .TE
 644 .TP
 645 .B TIOCMIWAIT
 646 Argument:
 647 .BI "int " arg
 648 .IP
 649 Wait for any of the 4 modem bits (DCD, RI, DSR, CTS) to change.
 650 The bits of interest are specified as a bit mask in
 651 .IR arg ,
 652 by ORing together any of the bit values,
 653 .BR TIOCM_RNG ,
 654 .BR TIOCM_DSR ,
 655 .BR TIOCM_CD ,
 656 and
 657 .BR TIOCM_CTS .
 658 The caller should use
 659 .B TIOCGICOUNT
 660 to see which bit has changed.
 661 .TP
 662 .B TIOCGICOUNT
 663 Argument:
 664 .BI "struct serial_icounter_struct\~*" argp
 665 .IP
 666 Get counts of input serial line interrupts (DCD, RI, DSR, CTS).
 667 The counts are written to the
 668 .I serial_icounter_struct
 669 structure pointed to by
 670 .IR argp .
 671 .IP
 672 Note: both 1->0 and 0->1 transitions are counted, except for
 673 RI, where only 0->1 transitions are counted.
 674 .SS Marking a line as local
 675 .TP
 676 .B TIOCGSOFTCAR
 677 Argument:
 678 .BI "int\~*" argp
 679 .IP
 680 ("Get software carrier flag")
 681 Get the status of the CLOCAL flag in the c_cflag field of the
 682 .I termios
 683 structure.
 684 .TP
 685 .B TIOCSSOFTCAR
 686 Argument:
 687 .BI "const int\~*" argp
 688 .IP
 689 ("Set software carrier flag")
 690 Set the CLOCAL flag in the
 691 .I termios
 692 structure when
 693 .RI * argp
 694 is nonzero, and clear it otherwise.
 695 .PP
 696 If the
 697 .B CLOCAL
 698 flag for a line is off, the hardware carrier detect (DCD)
 699 signal is significant, and an
 700 .BR open (2)
 701 of the corresponding terminal will block until DCD is asserted,
 702 unless the
 703 .B O_NONBLOCK
 704 flag is given.
 705 If
 706 .B CLOCAL
 707 is set, the line behaves as if DCD is always asserted.
 708 The software carrier flag is usually turned on for local devices,
 709 and is off for lines with modems.
 710 .SS Linux-specific
 711 For the
 712 .B TIOCLINUX
 713 ioctl, see
 714 .BR ioctl_console (2).
 715 .SS Kernel debugging
 716 .B "#include <linux/tty.h>"
 717 .TP
 718 .B TIOCTTYGSTRUCT
 719 Argument:
 720 .BI "struct tty_struct\~*" argp
 721 .IP
 722 Get the
 723 .I tty_struct
 724 corresponding to
 725 .IR fd .
 726 This command was removed in Linux 2.5.67.
 727 .\"     commit b3506a09d15dc5aee6d4bb88d759b157016e1864
 728 .\"     Author: Andries E. Brouwer <andries.brouwer@cwi.nl>
 729 .\"     Date:   Tue Apr 1 04:42:46 2003 -0800
 730 .\"
 731 .\"     [PATCH] kill TIOCTTYGSTRUCT
 732 .\"
 733 .\"     Only used for (dubious) debugging purposes, and exposes
 734 .\"     internal kernel state.
 735 .\"
 736 .\" .SS Serial info
 737 .\" .BR "#include <linux/serial.h>"
 738 .\" .PP
 739 .\" .TP
 740 .\" .BI "TIOCGSERIAL    struct serial_struct *" argp
 741 .\" Get serial info.
 742 .\" .TP
 743 .\" .BI "TIOCSSERIAL    const struct serial_struct *" argp
 744 .\" Set serial info.
 745 .SH RETURN VALUE
 746 The
 747 .BR ioctl (2)
 748 system call returns 0 on success.
 749 On error, it returns \-1 and sets
 750 .I errno
 751 to indicate the error.
 752 .SH ERRORS
 753 .TP
 754 .B EINVAL
 755 Invalid command parameter.
 756 .TP
 757 .B ENOIOCTLCMD
 758 Unknown command.
 759 .TP
 760 .B ENOTTY
 761 Inappropriate
 762 .IR fd .
 763 .TP
 764 .B EPERM
 765 Insufficient permission.
 766 .SH EXAMPLES
 767 Check the condition of DTR on the serial port.
 768 .PP
 769 .\" SRC BEGIN (tiocmget.c)
 770 .EX
 771 #include <fcntl.h>
 772 #include <stdio.h>
 773 #include <sys/ioctl.h>
 774 #include <unistd.h>
 775
 776 int
 777 main(void)
 778 {
 779     int fd, serial;
 780
 781     fd = open("/dev/ttyS0", O_RDONLY);
 782     ioctl(fd, TIOCMGET, &serial);
 783     if (serial & TIOCM_DTR)
 784         puts("TIOCM_DTR is set");
 785     else
 786         puts("TIOCM_DTR is not set");
 787     close(fd);
 788 }
 789 .EE
 790 .\" SRC END
 791 .PP
 792 Get or set arbitrary baudrate on the serial port.
 793 .PP
 794 .\" SRC BEGIN (tcgets.c)
 795 .EX
 796 /* SPDX-License-Identifier: GPL-2.0-or-later */
 797
 798 #include <asm/termbits.h>
 799 #include <fcntl.h>
 800 #include <stdio.h>
 801 #include <stdlib.h>
 802 #include <sys/ioctl.h>
 803 #include <unistd.h>
 804
 805 int
 806 main(int argc, char *argv[])
 807 {
 808 #if !defined BOTHER
 809     fprintf(stderr, "BOTHER is unsupported\en");
 810     /* Program may fallback to TCGETS/TCSETS with Bnnn constants */
 811     exit(EXIT_FAILURE);
 812 #else
 813     /* Declare tio structure, its type depends on supported ioctl */
 814 # if defined TCGETS2
 815     struct termios2 tio;
 816 # else
 817     struct termios tio;
 818 # endif
 819     int fd, rc;
 820
 821     if (argc != 2 && argc != 3 && argc != 4) {
 822         fprintf(stderr, "Usage: %s device [output [input] ]\en", argv[0]);
 823         exit(EXIT_FAILURE);
 824     }
 825
 826     fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
 827     if (fd < 0) {
 828         perror("open");
 829         exit(EXIT_FAILURE);
 830     }
 831
 832     /* Get the current serial port settings via supported ioctl */
 833 # if defined TCGETS2
 834     rc = ioctl(fd, TCGETS2, &tio);
 835 # else
 836     rc = ioctl(fd, TCGETS, &tio);
 837 # endif
 838     if (rc) {
 839         perror("TCGETS");
 840         close(fd);
 841         exit(EXIT_FAILURE);
 842     }
 843
 844     /* Change baud rate when more arguments were provided */
 845     if (argc == 3 || argc == 4) {
 846         /* Clear the current output baud rate and fill a new value */
 847         tio.c_cflag &= \(tiCBAUD;
 848         tio.c_cflag |= BOTHER;
 849         tio.c_ospeed = atoi(argv[2]);
 850
 851         /* Clear the current input baud rate and fill a new value */
 852         tio.c_cflag &= \(ti(CBAUD << IBSHIFT);
 853         tio.c_cflag |= BOTHER << IBSHIFT;
 854         /* When 4th argument is not provided reuse output baud rate */
 855         tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);
 856
 857         /* Set new serial port settings via supported ioctl */
 858 # if defined TCSETS2
 859         rc = ioctl(fd, TCSETS2, &tio);
 860 # else
 861         rc = ioctl(fd, TCSETS, &tio);
 862 # endif
 863         if (rc) {
 864             perror("TCSETS");
 865             close(fd);
 866             exit(EXIT_FAILURE);
 867         }
 868
 869         /* And get new values which were really configured */
 870 # if defined TCGETS2
 871         rc = ioctl(fd, TCGETS2, &tio);
 872 # else
 873         rc = ioctl(fd, TCGETS, &tio);
 874 # endif
 875         if (rc) {
 876             perror("TCGETS");
 877             close(fd);
 878             exit(EXIT_FAILURE);
 879         }
 880     }
 881
 882     close(fd);
 883
 884     printf("output baud rate: %u\en", tio.c_ospeed);
 885     printf("input baud rate: %u\en", tio.c_ispeed);
 886
 887     exit(EXIT_SUCCESS);
 888 #endif
 889 }
 890 .EE
 891 .\" SRC END
 892 .SH SEE ALSO
 893 .BR ldattach (8),
 894 .BR ioctl (2),
 895 .BR ioctl_console (2),
 896 .BR termios (3),
 897 .BR pty (7)
 898 .\"
 899 .\" FIONBIO                     const int *
 900 .\" FIONCLEX                    void
 901 .\" FIOCLEX                     void
 902 .\" FIOASYNC                    const int *
 903 .\" from serial.c:
 904 .\" TIOCSERCONFIG               void
 905 .\" TIOCSERGWILD                int *
 906 .\" TIOCSERSWILD                const int *
 907 .\" TIOCSERGSTRUCT              struct async_struct *
 908 .\" TIOCSERGETMULTI             struct serial_multiport_struct *
 909 .\" TIOCSERSETMULTI             const struct serial_multiport_struct *
 910 .\" TIOCGSERIAL, TIOCSSERIAL (see above)