man2/ioctl_tty.2

   1 '\" t
   2 .\" Copyright 2002 Walter Harms <walter.harms@informatik.uni-oldenburg.de>
   3 .\" and Andries Brouwer <aeb@cwi.nl>.
   4 .\"
   5 .\" SPDX-License-Identifier: GPL-1.0-or-later
   6 .\"
   7 .TH ioctl_tty 2 (date) "Linux man-pages (unreleased)"
   8 .SH NAME
   9 ioctl_tty \- ioctls for terminals and serial lines
  10 .SH LIBRARY
  11 Standard C library
  12 .RI ( libc ", " \-lc )
  13 .SH SYNOPSIS
  14 .nf
  15 .B #include <sys/ioctl.h>
  16 .BR "#include <asm/termbits.h>" "   /* Definition of " "struct termios" ,
  17 .BR    "                               struct termios2" ", and"
  18 .BR    "                               Bnnn" ", " BOTHER ", " CBAUD ", " CLOCAL ,
  19 .BR    "                               TC*" { FLUSH , ON , OFF "} and other constants */"
  20 .PP
  21 .BI "int ioctl(int " fd ", int " cmd ", ...);"
  22 .fi
  23 .SH DESCRIPTION
  24 The
  25 .BR ioctl (2)
  26 call for terminals and serial ports accepts many possible command arguments.
  27 Most require a third argument, of varying type, here called
  28 .I argp
  29 or
  30 .IR arg .
  31 .PP
  32 Use of
  33 .BR ioctl ()
  34 makes for nonportable programs.
  35 Use the POSIX interface described in
  36 .BR termios (3)
  37 whenever possible.
  38 .PP
  39 Please note that
  40 .B struct termios
  41 from
  42 .I <asm/termbits.h>
  43 is different and incompatible with
  44 .B struct termios
  45 from
  46 .IR <termios.h> .
  47 These ioctl calls require
  48 .B struct termios
  49 from
  50 .IR <asm/termbits.h> .
  51 .SS Get and set terminal attributes
  52 .TP
  53 .B TCGETS
  54 Argument:
  55 .BI "struct termios\~*" argp
  56 .IP
  57 Equivalent to
  58 .IR "tcgetattr(fd, argp)" .
  59 .IP
  60 Get the current serial port settings.
  61 .TP
  62 .B TCSETS
  63 Argument:
  64 .BI "const struct termios\~*" argp
  65 .IP
  66 Equivalent to
  67 .IR "tcsetattr(fd, TCSANOW, argp)" .
  68 .IP
  69 Set the current serial port settings.
  70 .TP
  71 .B TCSETSW
  72 Argument:
  73 .BI "const struct termios\~*" argp
  74 .IP
  75 Equivalent to
  76 .IR "tcsetattr(fd, TCSADRAIN, argp)" .
  77 .IP
  78 Allow the output buffer to drain, and
  79 set the current serial port settings.
  80 .TP
  81 .B TCSETSF
  82 Argument:
  83 .BI "const struct termios\~*" argp
  84 .IP
  85 Equivalent to
  86 .IR "tcsetattr(fd, TCSAFLUSH, argp)" .
  87 .IP
  88 Allow the output buffer to drain, discard pending input, and
  89 set the current serial port settings.
  90 .PP
  91 The following four ioctls, added in Linux 2.6.20,
  92 .\" commit 64bb6c5e1ddcd47c951740485026ef08975ee2e6
  93 .\" commit 592ee3a5e5e2a981ef2829a0380093006d045661
  94 are just like
  95 .BR TCGETS ,
  96 .BR TCSETS ,
  97 .BR TCSETSW ,
  98 .BR TCSETSF ,
  99 except that they take a
 100 .I "struct termios2\~*"
 101 instead of a
 102 .IR "struct termios\~*" .
 103 If the structure member
 104 .B c_cflag
 105 contains the flag
 106 .BR BOTHER ,
 107 then the baud rate is stored in the structure members
 108 .B c_ispeed
 109 and
 110 .B c_ospeed
 111 as integer values.
 112 These ioctls are not supported on all architectures.
 113 .RS
 114 .TS
 115 lb l.
 116 TCGETS2 \fBstruct termios2 *\fPargp
 117 TCSETS2 \fBconst struct termios2 *\fPargp
 118 TCSETSW2        \fBconst struct termios2 *\fPargp
 119 TCSETSF2        \fBconst struct termios2 *\fPargp
 120 .TE
 121 .RE
 122 .PP
 123 The following four ioctls are just like
 124 .BR TCGETS ,
 125 .BR TCSETS ,
 126 .BR TCSETSW ,
 127 .BR TCSETSF ,
 128 except that they take a
 129 .I "struct termio\~*"
 130 instead of a
 131 .IR "struct termios\~*" .
 132 .RS
 133 .TS
 134 lb l.
 135 TCGETA  \fBstruct termio *\fPargp
 136 TCSETA  \fBconst struct termio *\fPargp
 137 TCSETAW \fBconst struct termio *\fPargp
 138 TCSETAF \fBconst struct termio *\fPargp
 139 .TE
 140 .RE
 141 .SS Locking the termios structure
 142 The
 143 .I termios
 144 structure of a terminal can be locked.
 145 The lock is itself a
 146 .I termios
 147 structure, with nonzero bits or fields indicating a
 148 locked value.
 149 .TP
 150 .B TIOCGLCKTRMIOS
 151 Argument:
 152 .BI "struct termios\~*" argp
 153 .IP
 154 Gets the locking status of the
 155 .I termios
 156 structure of the terminal.
 157 .TP
 158 .B TIOCSLCKTRMIOS
 159 Argument:
 160 .BI "const struct termios\~*" argp
 161 .IP
 162 Sets the locking status of the
 163 .I termios
 164 structure of the terminal.
 165 Only a process with the
 166 .B CAP_SYS_ADMIN
 167 capability can do this.
 168 .SS Get and set window size
 169 Window sizes are kept in the kernel, but not used by the kernel
 170 (except in the case of virtual consoles, where the kernel will
 171 update the window size when the size of the virtual console changes,
 172 for example, by loading a new font).
 173 .TP
 174 .B TIOCGWINSZ
 175 Argument:
 176 .BI "struct winsize\~*" argp
 177 .IP
 178 Get window size.
 179 .TP
 180 .B TIOCSWINSZ
 181 Argument:
 182 .BI "const struct winsize\~*" argp
 183 .IP
 184 Set window size.
 185 .PP
 186 The struct used by these ioctls is defined as
 187 .PP
 188 .in +4n
 189 .EX
 190 struct winsize {
 191     unsigned short ws_row;
 192     unsigned short ws_col;
 193     unsigned short ws_xpixel;   /* unused */
 194     unsigned short ws_ypixel;   /* unused */
 195 };
 196 .EE
 197 .in
 198 .PP
 199 When the window size changes, a
 200 .B SIGWINCH
 201 signal is sent to the
 202 foreground process group.
 203 .SS Sending a break
 204 .TP
 205 .B TCSBRK
 206 Argument:
 207 .BI "int " arg
 208 .IP
 209 Equivalent to
 210 .IR "tcsendbreak(fd, arg)" .
 211 .IP
 212 If the terminal is using asynchronous serial data transmission, and
 213 .I arg
 214 is zero, then send a break (a stream of zero bits) for between
 215 0.25 and 0.5 seconds.
 216 If the terminal is not using asynchronous
 217 serial data transmission, then either a break is sent, or the function
 218 returns without doing anything.
 219 When
 220 .I arg
 221 is nonzero, nobody knows what will happen.
 222 .IP
 223 (SVr4, UnixWare, Solaris, and Linux treat
 224 .I "tcsendbreak(fd,arg)"
 225 with nonzero
 226 .I arg
 227 like
 228 .IR "tcdrain(fd)" .
 229 SunOS treats
 230 .I arg
 231 as a multiplier, and sends a stream of bits
 232 .I arg
 233 times as long as done for zero
 234 .IR arg .
 235 DG/UX and AIX treat
 236 .I arg
 237 (when nonzero) as a time interval measured in milliseconds.
 238 HP-UX ignores
 239 .IR arg .)
 240 .TP
 241 .B TCSBRKP
 242 Argument:
 243 .BI "int " arg
 244 .IP
 245 So-called "POSIX version" of
 246 .BR TCSBRK .
 247 It treats nonzero
 248 .I arg
 249 as a time interval measured in deciseconds, and does nothing
 250 when the driver does not support breaks.
 251 .TP
 252 .B TIOCSBRK
 253 Argument:
 254 .B void
 255 .IP
 256 Turn break on, that is, start sending zero bits.
 257 .TP
 258 .B TIOCCBRK
 259 Argument:
 260 .B void
 261 .IP
 262 Turn break off, that is, stop sending zero bits.
 263 .SS Software flow control
 264 .TP
 265 .B TCXONC
 266 Argument:
 267 .BI "int " arg
 268 .IP
 269 Equivalent to
 270 .IR "tcflow(fd, arg)" .
 271 .IP
 272 See
 273 .BR tcflow (3)
 274 for the argument values
 275 .BR TCOOFF ,
 276 .BR TCOON ,
 277 .BR TCIOFF ,
 278 .BR TCION .
 279 .SS Buffer count and flushing
 280 .TP
 281 .B FIONREAD
 282 Argument:
 283 .BI "int\~*" argp
 284 .IP
 285 Get the number of bytes in the input buffer.
 286 .TP
 287 .B TIOCINQ
 288 Argument:
 289 .BI "int\~*" argp
 290 .IP
 291 Same as
 292 .BR FIONREAD .
 293 .TP
 294 .B TIOCOUTQ
 295 Argument:
 296 .BI "int\~*" argp
 297 .IP
 298 Get the number of bytes in the output buffer.
 299 .TP
 300 .B TCFLSH
 301 Argument:
 302 .BI "int " arg
 303 .IP
 304 Equivalent to
 305 .IR "tcflush(fd, arg)" .
 306 .IP
 307 See
 308 .BR tcflush (3)
 309 for the argument values
 310 .BR TCIFLUSH ,
 311 .BR TCOFLUSH ,
 312 .BR TCIOFLUSH .
 313 .TP
 314 .B TIOCSERGETLSR
 315 Argument:
 316 .BI "int\~*" argp
 317 .IP
 318 Get line status register.
 319 Status register has
 320 .B TIOCSER_TEMT
 321 bit set when
 322 output buffer is empty and also hardware transmitter is physically empty.
 323 .IP
 324 Does not have to be supported by all serial tty drivers.
 325 .IP
 326 .BR tcdrain (3)
 327 does not wait and returns immediately when
 328 .B TIOCSER_TEMT
 329 bit is set.
 330 .SS Faking input
 331 .TP
 332 .B TIOCSTI
 333 Argument:
 334 .BI "const char\~*" argp
 335 .IP
 336 Insert the given byte in the input queue.
 337 .SS Redirecting console output
 338 .TP
 339 .B TIOCCONS
 340 Argument:
 341 .B void
 342 .IP
 343 Redirect output that would have gone to
 344 .I /dev/console
 345 or
 346 .I /dev/tty0
 347 to the given terminal.
 348 If that was a pseudoterminal master, send it to the slave.
 349 Before Linux 2.6.10,
 350 anybody can do this as long as the output was not redirected yet;
 351 since Linux 2.6.10, only a process with the
 352 .B CAP_SYS_ADMIN
 353 capability may do this.
 354 If output was redirected already, then
 355 .B EBUSY
 356 is returned,
 357 but redirection can be stopped by using this ioctl with
 358 .I fd
 359 pointing at
 360 .I /dev/console
 361 or
 362 .IR /dev/tty0 .
 363 .SS Controlling terminal
 364 .TP
 365 .B TIOCSCTTY
 366 Argument:
 367 .BI "int " arg
 368 .IP
 369 Make the given terminal the controlling terminal of the calling process.
 370 The calling process must be a session leader and not have a
 371 controlling terminal already.
 372 For this case,
 373 .I arg
 374 should be specified as zero.
 375 .IP
 376 If this terminal is already the controlling terminal
 377 of a different session group, then the ioctl fails with
 378 .BR EPERM ,
 379 unless the caller has the
 380 .B CAP_SYS_ADMIN
 381 capability and
 382 .I arg
 383 equals 1, in which case the terminal is stolen, and all processes that had
 384 it as controlling terminal lose it.
 385 .TP
 386 .B TIOCNOTTY
 387 Argument:
 388 .B void
 389 .IP
 390 If the given terminal was the controlling terminal of the calling process,
 391 give up this controlling terminal.
 392 If the process was session leader,
 393 then send
 394 .B SIGHUP
 395 and
 396 .B SIGCONT
 397 to the foreground process group
 398 and all processes in the current session lose their controlling terminal.
 399 .SS Process group and session ID
 400 .TP
 401 .B TIOCGPGRP
 402 Argument:
 403 .BI "pid_t\~*" argp
 404 .IP
 405 When successful, equivalent to
 406 .IR "*argp = tcgetpgrp(fd)" .
 407 .IP
 408 Get the process group ID of the foreground process group on this terminal.
 409 .TP
 410 .B TIOCSPGRP
 411 Argument:
 412 .BI "const pid_t\~*" argp
 413 .IP
 414 Equivalent to
 415 .IR "tcsetpgrp(fd, *argp)" .
 416 .IP
 417 Set the foreground process group ID of this terminal.
 418 .TP
 419 .B TIOCGSID
 420 Argument:
 421 .BI "pid_t\~*" argp
 422 .IP
 423 When successful, equivalent to
 424 .IR "*argp = tcgetsid(fd)" .
 425 .IP
 426 Get the session ID of the given terminal.
 427 This fails with the error
 428 .B ENOTTY
 429 if the terminal is not a master pseudoterminal
 430 and not our controlling terminal.
 431 Strange.
 432 .SS Exclusive mode
 433 .TP
 434 .B TIOCEXCL
 435 Argument:
 436 .B void
 437 .IP
 438 Put the terminal into exclusive mode.
 439 No further
 440 .BR open (2)
 441 operations on the terminal are permitted.
 442 (They fail with
 443 .BR EBUSY ,
 444 except for a process with the
 445 .B CAP_SYS_ADMIN
 446 capability.)
 447 .TP
 448 .B TIOCGEXCL
 449 Argument:
 450 .BI "int\~*" argp
 451 .IP
 452 (since Linux 3.8)
 453 If the terminal is currently in exclusive mode,
 454 place a nonzero value in the location pointed to by
 455 .IR argp ;
 456 otherwise, place zero in
 457 .IR *argp .
 458 .TP
 459 .B TIOCNXCL
 460 Argument:
 461 .B void
 462 .IP
 463 Disable exclusive mode.
 464 .SS Line discipline
 465 .TP
 466 .B TIOCGETD
 467 Argument:
 468 .BI "int\~*" argp
 469 .IP
 470 Get the line discipline of the terminal.
 471 .TP
 472 .B TIOCSETD
 473 Argument:
 474 .BI "const int\~*" argp
 475 .IP
 476 Set the line discipline of the terminal.
 477 .SS Pseudoterminal ioctls
 478 .TP
 479 .B TIOCPKT
 480 Argument:
 481 .BI "const int\~*" argp
 482 .IP
 483 Enable (when
 484 .RI * argp
 485 is nonzero) or disable packet mode.
 486 Can be applied to the master side of a pseudoterminal only (and will return
 487 .B ENOTTY
 488 otherwise).
 489 In packet mode, each subsequent
 490 .BR read (2)
 491 will return a packet that either contains a single nonzero control byte,
 492 or has a single byte containing zero (\(aq\e0\(aq) followed by data
 493 written on the slave side of the pseudoterminal.
 494 If the first byte is not
 495 .B TIOCPKT_DATA
 496 (0), it is an OR of one
 497 or more of the following bits:
 498 .IP
 499 .ad l
 500 .TS
 501 lb l.
 502 TIOCPKT_FLUSHREAD       T{
 503 The read queue for the terminal is flushed.
 504 T}
 505 TIOCPKT_FLUSHWRITE      T{
 506 The write queue for the terminal is flushed.
 507 T}
 508 TIOCPKT_STOP    T{
 509 Output to the terminal is stopped.
 510 T}
 511 TIOCPKT_START   T{
 512 Output to the terminal is restarted.
 513 T}
 514 TIOCPKT_DOSTOP  T{
 515 The start and stop characters are \fB\(haS\fP/\fB\(haQ\fP.
 516 T}
 517 TIOCPKT_NOSTOP  T{
 518 The start and stop characters are not \fB\(haS\fP/\fB\(haQ\fP.
 519 T}
 520 .TE
 521 .ad
 522 .IP
 523 While packet mode is in use, the presence
 524 of control status information to be read
 525 from the master side may be detected by a
 526 .BR select (2)
 527 for exceptional conditions or a
 528 .BR poll (2)
 529 for the
 530 .B POLLPRI
 531 event.
 532 .IP
 533 This mode is used by
 534 .BR rlogin (1)
 535 and
 536 .BR rlogind (8)
 537 to implement a remote-echoed,
 538 locally \fB\(haS\fP/\fB\(haQ\fP flow-controlled remote login.
 539 .TP
 540 .B TIOCGPKT
 541 Argument:
 542 .BI "const int\~*" argp
 543 .IP
 544 (since Linux 3.8)
 545 Return the current packet mode setting in the integer pointed to by
 546 .IR argp .
 547 .TP
 548 .B TIOCSPTLCK
 549 Argument:
 550 .BI "int\~*" argp
 551 .IP
 552 Set (if
 553 .I *argp
 554 is nonzero) or remove (if
 555 .I *argp
 556 is zero) the lock on the pseudoterminal slave device.
 557 (See also
 558 .BR unlockpt (3).)
 559 .TP
 560 .B TIOCGPTLCK
 561 Argument:
 562 .BI "int\~*" argp
 563 .IP
 564 (since Linux 3.8)
 565 Place the current lock state of the pseudoterminal slave device
 566 in the location pointed to by
 567 .IR argp .
 568 .TP
 569 .B TIOCGPTPEER
 570 Argument:
 571 .BI "int " flags
 572 .IP
 573 .\" commit 54ebbfb1603415d9953c150535850d30609ef077
 574 (since Linux 4.13)
 575 Given a file descriptor in
 576 .I fd
 577 that refers to a pseudoterminal master,
 578 open (with the given
 579 .BR open (2)-style
 580 .IR flags )
 581 and return a new file descriptor that refers to the peer
 582 pseudoterminal slave device.
 583 This operation can be performed
 584 regardless of whether the pathname of the slave device
 585 is accessible through the calling process's mount namespace.
 586 .IP
 587 Security-conscious programs interacting with namespaces may wish to use this
 588 operation rather than
 589 .BR open (2)
 590 with the pathname returned by
 591 .BR ptsname (3),
 592 and similar library functions that have insecure APIs.
 593 (For example, confusion can occur in some cases using
 594 .BR ptsname (3)
 595 with a pathname where a devpts filesystem
 596 has been mounted in a different mount namespace.)
 597 .PP
 598 The BSD ioctls
 599 .BR TIOCSTOP ,
 600 .BR TIOCSTART ,
 601 .BR TIOCUCNTL ,
 602 and
 603 .B TIOCREMOTE
 604 have not been implemented under Linux.
 605 .SS Modem control
 606 .TP
 607 .B TIOCMGET
 608 Argument:
 609 .BI "int\~*" argp
 610 .IP
 611 Get the status of modem bits.
 612 .TP
 613 .B TIOCMSET
 614 Argument:
 615 .BI "const int\~*" argp
 616 .IP
 617 Set the status of modem bits.
 618 .TP
 619 .B TIOCMBIC
 620 Argument:
 621 .BI "const int\~*" argp
 622 .IP
 623 Clear the indicated modem bits.
 624 .TP
 625 .B TIOCMBIS
 626 Argument:
 627 .BI "const int\~*" argp
 628 .IP
 629 Set the indicated modem bits.
 630 .PP
 631 The following bits are used by the above ioctls:
 632 .PP
 633 .TS
 634 lb l.
 635 TIOCM_LE        DSR (data set ready/line enable)
 636 TIOCM_DTR       DTR (data terminal ready)
 637 TIOCM_RTS       RTS (request to send)
 638 TIOCM_ST        Secondary TXD (transmit)
 639 TIOCM_SR        Secondary RXD (receive)
 640 TIOCM_CTS       CTS (clear to send)
 641 TIOCM_CAR       DCD (data carrier detect)
 642 TIOCM_CD        see TIOCM_CAR
 643 TIOCM_RNG       RNG (ring)
 644 TIOCM_RI        see TIOCM_RNG
 645 TIOCM_DSR       DSR (data set ready)
 646 .TE
 647 .TP
 648 .B TIOCMIWAIT
 649 Argument:
 650 .BI "int " arg
 651 .IP
 652 Wait for any of the 4 modem bits (DCD, RI, DSR, CTS) to change.
 653 The bits of interest are specified as a bit mask in
 654 .IR arg ,
 655 by ORing together any of the bit values,
 656 .BR TIOCM_RNG ,
 657 .BR TIOCM_DSR ,
 658 .BR TIOCM_CD ,
 659 and
 660 .BR TIOCM_CTS .
 661 The caller should use
 662 .B TIOCGICOUNT
 663 to see which bit has changed.
 664 .TP
 665 .B TIOCGICOUNT
 666 Argument:
 667 .BI "struct serial_icounter_struct\~*" argp
 668 .IP
 669 Get counts of input serial line interrupts (DCD, RI, DSR, CTS).
 670 The counts are written to the
 671 .I serial_icounter_struct
 672 structure pointed to by
 673 .IR argp .
 674 .IP
 675 Note: both 1->0 and 0->1 transitions are counted, except for
 676 RI, where only 0->1 transitions are counted.
 677 .SS Marking a line as local
 678 .TP
 679 .B TIOCGSOFTCAR
 680 Argument:
 681 .BI "int\~*" argp
 682 .IP
 683 ("Get software carrier flag")
 684 Get the status of the CLOCAL flag in the c_cflag field of the
 685 .I termios
 686 structure.
 687 .TP
 688 .B TIOCSSOFTCAR
 689 Argument:
 690 .BI "const int\~*" argp
 691 .IP
 692 ("Set software carrier flag")
 693 Set the CLOCAL flag in the
 694 .I termios
 695 structure when
 696 .RI * argp
 697 is nonzero, and clear it otherwise.
 698 .PP
 699 If the
 700 .B CLOCAL
 701 flag for a line is off, the hardware carrier detect (DCD)
 702 signal is significant, and an
 703 .BR open (2)
 704 of the corresponding terminal will block until DCD is asserted,
 705 unless the
 706 .B O_NONBLOCK
 707 flag is given.
 708 If
 709 .B CLOCAL
 710 is set, the line behaves as if DCD is always asserted.
 711 The software carrier flag is usually turned on for local devices,
 712 and is off for lines with modems.
 713 .SS Linux-specific
 714 For the
 715 .B TIOCLINUX
 716 ioctl, see
 717 .BR ioctl_console (2).
 718 .SS Kernel debugging
 719 .B "#include <linux/tty.h>"
 720 .TP
 721 .B TIOCTTYGSTRUCT
 722 Argument:
 723 .BI "struct tty_struct\~*" argp
 724 .IP
 725 Get the
 726 .I tty_struct
 727 corresponding to
 728 .IR fd .
 729 This command was removed in Linux 2.5.67.
 730 .\"     commit b3506a09d15dc5aee6d4bb88d759b157016e1864
 731 .\"     Author: Andries E. Brouwer <andries.brouwer@cwi.nl>
 732 .\"     Date:   Tue Apr 1 04:42:46 2003 -0800
 733 .\"
 734 .\"     [PATCH] kill TIOCTTYGSTRUCT
 735 .\"
 736 .\"     Only used for (dubious) debugging purposes, and exposes
 737 .\"     internal kernel state.
 738 .\"
 739 .\" .SS Serial info
 740 .\" .BR "#include <linux/serial.h>"
 741 .\" .PP
 742 .\" .TP
 743 .\" .BI "TIOCGSERIAL    struct serial_struct *" argp
 744 .\" Get serial info.
 745 .\" .TP
 746 .\" .BI "TIOCSSERIAL    const struct serial_struct *" argp
 747 .\" Set serial info.
 748 .SH RETURN VALUE
 749 The
 750 .BR ioctl (2)
 751 system call returns 0 on success.
 752 On error, it returns \-1 and sets
 753 .I errno
 754 to indicate the error.
 755 .SH ERRORS
 756 .TP
 757 .B EINVAL
 758 Invalid command parameter.
 759 .TP
 760 .B ENOIOCTLCMD
 761 Unknown command.
 762 .TP
 763 .B ENOTTY
 764 Inappropriate
 765 .IR fd .
 766 .TP
 767 .B EPERM
 768 Insufficient permission.
 769 .SH EXAMPLES
 770 Check the condition of DTR on the serial port.
 771 .PP
 772 .\" SRC BEGIN (tiocmget.c)
 773 .EX
 774 #include <fcntl.h>
 775 #include <stdio.h>
 776 #include <sys/ioctl.h>
 777 #include <unistd.h>
 778
 779 int
 780 main(void)
 781 {
 782     int fd, serial;
 783
 784     fd = open("/dev/ttyS0", O_RDONLY);
 785     ioctl(fd, TIOCMGET, &serial);
 786     if (serial & TIOCM_DTR)
 787         puts("TIOCM_DTR is set");
 788     else
 789         puts("TIOCM_DTR is not set");
 790     close(fd);
 791 }
 792 .EE
 793 .\" SRC END
 794 .PP
 795 Get or set arbitrary baudrate on the serial port.
 796 .PP
 797 .\" SRC BEGIN (tcgets.c)
 798 .EX
 799 /* SPDX-License-Identifier: GPL-2.0-or-later */
 800
 801 #include <asm/termbits.h>
 802 #include <fcntl.h>
 803 #include <stdio.h>
 804 #include <stdlib.h>
 805 #include <sys/ioctl.h>
 806 #include <unistd.h>
 807
 808 int
 809 main(int argc, char *argv[])
 810 {
 811 #if !defined BOTHER
 812     fprintf(stderr, "BOTHER is unsupported\en");
 813     /* Program may fallback to TCGETS/TCSETS with Bnnn constants */
 814     exit(EXIT_FAILURE);
 815 #else
 816     /* Declare tio structure, its type depends on supported ioctl */
 817 # if defined TCGETS2
 818     struct termios2 tio;
 819 # else
 820     struct termios tio;
 821 # endif
 822     int fd, rc;
 823
 824     if (argc != 2 && argc != 3 && argc != 4) {
 825         fprintf(stderr, "Usage: %s device [output [input] ]\en", argv[0]);
 826         exit(EXIT_FAILURE);
 827     }
 828
 829     fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
 830     if (fd < 0) {
 831         perror("open");
 832         exit(EXIT_FAILURE);
 833     }
 834
 835     /* Get the current serial port settings via supported ioctl */
 836 # if defined TCGETS2
 837     rc = ioctl(fd, TCGETS2, &tio);
 838 # else
 839     rc = ioctl(fd, TCGETS, &tio);
 840 # endif
 841     if (rc) {
 842         perror("TCGETS");
 843         close(fd);
 844         exit(EXIT_FAILURE);
 845     }
 846
 847     /* Change baud rate when more arguments were provided */
 848     if (argc == 3 || argc == 4) {
 849         /* Clear the current output baud rate and fill a new value */
 850         tio.c_cflag &= \(tiCBAUD;
 851         tio.c_cflag |= BOTHER;
 852         tio.c_ospeed = atoi(argv[2]);
 853
 854         /* Clear the current input baud rate and fill a new value */
 855         tio.c_cflag &= \(ti(CBAUD << IBSHIFT);
 856         tio.c_cflag |= BOTHER << IBSHIFT;
 857         /* When 4th argument is not provided reuse output baud rate */
 858         tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);
 859
 860         /* Set new serial port settings via supported ioctl */
 861 # if defined TCSETS2
 862         rc = ioctl(fd, TCSETS2, &tio);
 863 # else
 864         rc = ioctl(fd, TCSETS, &tio);
 865 # endif
 866         if (rc) {
 867             perror("TCSETS");
 868             close(fd);
 869             exit(EXIT_FAILURE);
 870         }
 871
 872         /* And get new values which were really configured */
 873 # if defined TCGETS2
 874         rc = ioctl(fd, TCGETS2, &tio);
 875 # else
 876         rc = ioctl(fd, TCGETS, &tio);
 877 # endif
 878         if (rc) {
 879             perror("TCGETS");
 880             close(fd);
 881             exit(EXIT_FAILURE);
 882         }
 883     }
 884
 885     close(fd);
 886
 887     printf("output baud rate: %u\en", tio.c_ospeed);
 888     printf("input baud rate: %u\en", tio.c_ispeed);
 889
 890     exit(EXIT_SUCCESS);
 891 #endif
 892 }
 893 .EE
 894 .\" SRC END
 895 .SH SEE ALSO
 896 .BR ldattach (8),
 897 .BR ioctl (2),
 898 .BR ioctl_console (2),
 899 .BR termios (3),
 900 .BR pty (7)
 901 .\"
 902 .\" FIONBIO                     const int *
 903 .\" FIONCLEX                    void
 904 .\" FIOCLEX                     void
 905 .\" FIOASYNC                    const int *
 906 .\" from serial.c:
 907 .\" TIOCSERCONFIG               void
 908 .\" TIOCSERGWILD                int *
 909 .\" TIOCSERSWILD                const int *
 910 .\" TIOCSERGSTRUCT              struct async_struct *
 911 .\" TIOCSERGETMULTI             struct serial_multiport_struct *
 912 .\" TIOCSERSETMULTI             const struct serial_multiport_struct *
 913 .\" TIOCGSERIAL, TIOCSSERIAL (see above)