man2/ioctl_tty.2

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