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man pages section 4: Device and Network Interfaces

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Updated: Thursday, June 13, 2019
 
 

ttcompat(4M)

Name

ttcompat - V7, 4BSD and XENIX STREAMS compatibility module

Synopsis

#define BSD_COMP
#include <sys/stropts.h>
#include <sys/ioctl.h>
ioctl(fd, I_PUSH, "ttcompat");

Description

ttcompat is a STREAMS module that translates the ioctl calls supported by the older Version 7, 4BSD, and XENIX terminal drivers into the ioctl calls supported by the termio interface (see termio(4I)). All other messages pass through this module unchanged; the behavior of read and write calls is unchanged, as is the behavior of ioctl calls other than the ones supported by ttcompat.

This module can be automatically pushed onto a stream using the autopush mechanism when a terminal device is opened; it does not have to be explicitly pushed onto a stream. This module requires that the termios interface be supported by the modules and the application can push the driver downstream. The TCGETS, TCSETS, and TCSETSF ioctl calls must be supported. If any information set or fetched by those ioctl calls is not supported by the modules and driver downstream, some of the V7/4BSD/XENIX functions may not be supported. For example, if the CBAUD bits in the c_cflag field are not supported, the functions provided by the sg_ispeed and sg_ospeed fields of the sgttyb structure (see below) will not be supported. If the TCFLSH ioctl is not supported, the function provided by the TIOCFLUSH ioctl will not be supported. If the TCXONC ioctl is not supported, the functions provided by the TIOCSTOP and TIOCSTART ioctl calls will not be supported. If the TIOCMBIS and TIOCMBIC ioctl calls are not supported, the functions provided by the TIOCSDTR and TIOCCDTR ioctl calls will not be supported.

The basic ioctl calls use the sgttyb structure defined by <sys/ttold.h> (included by <sys/ioctl.h>):

struct   sgttyb   {
	char	sg_ispeed;
	char	sg_ospeed;
	char	sg_erase;
	char	sg_kill;
	int	sg_flags;
};

The sg_ispeed and sg_ospeed fields describe the input and output speeds of the device. If the speed set on the device is over B38400, then it is reported as B38400 for compatibility reasons. If it is set to B38400 and the current speed is over B38400, the change is ignored. See TIOCGETP and TIOCSETP below. The sg_erase and sg_kill fields of the argument structure specify the erase and kill characters respectively, and reflect the values in the VERASE and VKILL members of the c_cc field of the termios structure.

The sg_flags field of the argument structure contains several flags that determine the system's treatment of the terminal. They are mapped into flags in fields of the terminal state, represented by the termios structure.

Delay type 0 (NL0, TAB0, CR0, FF0, BS0) is always mapped into the equivalent delay type 0 in the c_oflag field of the termios structure. Other delay mappings are performed as follows:

sg_flags
c_oflag
BS1
BS1
FF1
VT1
CR1
CR2
CR2
CR3
CR3
CR0 (not supported)
TAB1
TAB1
TAB2
TAB2
XTABS
TAB3
NL1
ONLRET|CR1
NL2
NL1
NL3
NL0 (not supported)

If previous TIOCLSET or TIOCLBIS ioctl calls have not selected LITOUT or PASS8 mode, and if RAW mode is not selected, the ISTRIP flag is set in the c_iflag field of the termios structure, and the EVENP and ODDP flags control the parity of characters sent to the terminal and accepted from the terminal, as follows:

0 (neither EVENP nor ODDP)

Parity is not to be generated on output or checked on input. The character size is set to CS8 and the PARENB flag is cleared in the c_cflag field of the termios structure.

EVENP

Even parity characters are to be generated on output and accepted on input. The INPCK flag is set in the c_iflag field of the termios structure, the character size is set to CS7 and the PARENB flag is set in the c_iflag field of the termios structure.

ODDP

Odd parity characters are to be generated on output and accepted on input. The INPCK flag is set in the c_iflag, the character size is set to CS7 and the PARENB and PARODD flags are set in the c_iflag field of the termios structure.

EVENP|ODDP or ANYP

Even parity characters are to be generated on output and characters of either parity are to be accepted on input. The INPCK flag is cleared in the c_iflag field, the character size is set to CS7 and the PARENB flag is set in the c_iflag field of the termios structure.

The RAW flag disables all output processing (the OPOST flag in the c_oflag field, and the XCASE and IEXTEN flags in the c_iflag field are cleared in the termios structure) and input processing (all flags in the c_iflag field other than the IXOFF and IXANY flags are cleared in the termios structure). Eight bits of data, with no parity bit are accepted on input and generated on output; the character size is set to CS8 and the PARENB and PARODD flags are cleared in the c_cflag field of the termios structure. The signal-generating and line-editing control characters are disabled by clearing the ISIG and ICANON flags in the c_iflag field of the termios structure.

The CRMOD flag turns input carriage return characters into linefeed characters, and output linefeed characters to be sent as a carriage return followed by a linefeed. The ICRNL flag in the c_iflag field, and the OPOST and ONLCR flags in the c_oflag field, are set in the termios structure.

The LCASE flag maps upper-case letters in the ASCII character set to their lower-case equivalents on input (the IUCLC flag is set in the c_iflag field), and maps lower-case letters in the ASCII character set to their upper-case equivalents on output (the OLCUC flag is set in the c_oflag field). Escape sequences are accepted on input, and generated on output, to handle certain ASCII characters not supported by older terminals (the XCASE flag is set in the c_lflag field).

Other flags are directly mapped to flags in the termios structure:

sg_flags
Flags in termios structure
CBREAK
Complement of ICANON in c_lflag field
ECHO
ECHO in c_lflag field
TANDEM
IXOFF in c_iflag field

Another structure associated with each terminal specifies characters that are special in both the old Version 7 and the newer 4BSD terminal interfaces. The following structure is defined by <sys/ttold.h>:

struct   tchars   {
          char t_intrc;     /* interrupt */
          char t_quitc;     /* quit */
          char t_startc; /* start output */
          char t_stopc;     /* stop output */
          char t_eofc;        /* end-of-file */
          char t_brkc;        /* input delimiter (like nl) */
     };

XENIX defines the tchar structure as tc. The characters are mapped to members of the c_cc field of the termios structure as follows:


       tchars                c_cc index
       t_intrc               VINTR
       t_quitc               VQUIT
       t_startc              VSTART
       t_stopc               VSTOP
       t_eofc                VEOF
       t_brkc                VEOL

Also associated with each terminal is a local flag word (TIOCLSET and TIOCLGET), specifying flags supported by the new 4BSD terminal interface. Most of these flags are directly mapped to flags in the termios structure:

Local flags
Flags in termios structure
LCRTBS
Not supported
LPRTERA
ECHOPRT in the c_lflag field
LCRTERA
ECHOE in the c_lflag field
LTILDE
Not supported
LMDMBUF
Not supported
LTOSTOP
TOSTOP in the c_lflag field
LFLUSHO
FLUSHO in the c_lflag field
LNOHANG
CLOCAL in the c_cflag field
LCRTKIL
ECHOKE in the c_lflag field
LPASS8
CS8 in the c_cflag field
LCTLECH
CTLECH in the c_lflag field
LPENDIN
PENDIN in the c_lflag field
LDECCTQ
Complement of IXANY in the c_iflag field
LNOFLSH
NOFLSH in the c_lflag field

Each flag has a corresponding equivalent sg_flags value. The sg_flags definitions omit the leading L; for example, TIOCSETP with sg_flags set to TOSTOP is equivalent to TIOCLSET with LTOSTOP.

Another structure associated with each terminal is the ltchars structure which defines control characters for the new 4BSD terminal interface. Its structure is:

struct ltchars {
   char t_suspc;  /* stop process signal */
   char t_dsuspc; /* delayed stop process signal */
   char t_rprntc; /* reprint line */
   char t_flushc; /*flush output (toggles) */
   char t_werasc; /* word erase */
   char t_lnextc; /* literal next character */
};

The characters are mapped to members of the c_cc field of the termios structure as follows:

ltchars
c_cc index
t_suspc
VSUS
t_dsuspc
VDSUSP
t_rprntc
VREPRINT
t_flushc
VDISCARD
t_werasc
VWERASE
t_lnextc
VLNEXT

Ioctls

ttcompat responds to the following ioctl calls. All others are passed to the module below.

TIOCGETP

The argument is a pointer to an sgttyb structure. The current terminal state is fetched; the appropriate characters in the terminal state are stored in that structure, as are the input and output speeds. If the speed is over B38400, then B38400 is returned. The values of the flags in the sg_flags field are derived from the flags in the terminal state and stored in the structure.

TIOCEXCL

Set exclusive-use mode; no further opens are permitted until the file has been closed.

TIOCNXCL

Turn off exclusive-use mode.

TIOCSETP

The argument is a pointer to an sgttyb structure. The appropriate characters and input and output speeds in the terminal state are set from the values in that structure, and the flags in the terminal state are set to match the values of the flags in the sg_flags field of that structure. The state is changed with a TCSETSF ioctl so that the interface delays until output is quiescent, then throws away any unread characters, before changing the modes. If the current device speed is over B38400 for either input or output speed, and B38400 is specified through this interface for that speed, the actual device speed is not changed. If the device speed is B38400 or lower or if some speed other than B38400 is specified, then the actual speed specified is set.

TIOCSETN

The argument is a pointer to an sgttyb structure. The terminal state is changed as TIOCSETP would change it, but a TCSETS ioctl is used, so that the interface neither delays nor discards input.

TIOCHPCL

The argument is ignored. The HUPCL flag is set in the c_cflag word of the terminal state.

TIOCFLUSH

The argument is a pointer to an int variable. If its value is zero, all characters waiting in input or output queues are flushed. Otherwise, the value of the int is treated as the logical OR of the FREAD and FWRITE flags defined by <sys/file.h>. If the FREAD bit is set, all characters waiting in input queues are flushed, and if the FWRITE bit is set, all characters waiting in output queues are flushed.

TIOCSBRK

The argument is ignored. The break bit is set for the device. (This is not supported by ttcompat. The underlying driver must support TIOCSBRK.)

TIOCCBRK

The argument is ignored. The break bit is cleared for the device. (This is not supported by ttcompat. The underlying driver must support TIOCCBRK.)

TIOCSDTR

The argument is ignored. The Data Terminal Ready bit is set for the device.

TIOCCDTR

The argument is ignored. The Data Terminal Ready bit is cleared for the device.

TIOCSTOP

The argument is ignored. Output is stopped as if the STOP character had been typed.

TIOCSTART

The argument is ignored. Output is restarted as if the START character had been typed.

TIOCGETC

The argument is a pointer to a tchars structure. The current terminal state is fetched, and the appropriate characters in the terminal state are stored in that structure.

TIOCSETC

The argument is a pointer to a tchars structure. The values of the appropriate characters in the terminal state are set from the characters in that structure.

TIOCLGET

The argument is a pointer to an int. The current terminal state is fetched, and the values of the local flags are derived from the flags in the terminal state and stored in the int pointed to by the argument.

TIOCLBIS

The argument is a pointer to an int whose value is a mask containing flags to be set in the local flags word. The current terminal state is fetched, and the values of the local flags are derived from the flags in the terminal state; the specified flags are set, and the flags in the terminal state are set to match the new value of the local flags word.

TIOCLBIC

The argument is a pointer to an int whose value is a mask containing flags to be cleared in the local flags word. The current terminal state is fetched, and the values of the local flags are derived from the flags in the terminal state; the specified flags are cleared, and the flags in the terminal state are set to match the new value of the local flags word.

TIOCLSET

The argument is a pointer to an int containing a new set of local flags. The flags in the terminal state are set to match the new value of the local flags word. (This ioctl was added because sg_flags was once a 16 bit value. The local modes controlled by TIOCLSET are equivalent to the modes controlled by TIOCSETP and sg_flags.)

TIOCGLTC

The argument is a pointer to an ltchars structure. The values of the appropriate characters in the terminal state are stored in that structure.

TIOCSLTC

The argument is a pointer to an ltchars structure. The values of the appropriate characters in the terminal state are set from the characters in that structure.

FIORDCHK

Returns the number of immediately readable characters. The argument is ignored. (This ioctl is handled in the stream head, not in the ttcompat module.)

FIONREAD

Returns the number of immediately readable characters in the int pointed to by the argument. (This ioctl is handled in the stream head, not in the ttcompat module.)

The following ioctls are returned as successful for the sake of compatibility. However, nothing significant is done (that is, the state of the terminal is not changed in any way, and no message is passed through to the underlying tty driver).

         
DIOCSETP
DIOCSETP
DIOCGETP
LDCLOSE  
LDCHG
LDOPEN
LDGETT
LDSETT
TIOCGETD
TIOCSETD

The following old ioctls are not supported by ttcompat, but are supported by Solaris tty drivers. As with all ioctl not otherwise listed in this documentation, these are passed through to the underlying driver and are handled there.


TIOCREMOTE
TIOCGWINSZ 
TIOCSWINSZ

The following ioctls are not supported by ttcompat, and are generally not supported by Solaris tty drivers. They are passed through, and the tty drivers return EINVAL.


LDSMAP
LDGMAP 
LDNMAP
TIOCNOTTY
TIOCOUTQ

LDSMAP, LDGMAP, and LDNMAP are defined in <sys/termios.h>.

Support for TIOCNOTTY and TIOCSCTTY is provided natively by the stream head. Therefore, those ioctls never reach ttcompat or any STREAMS- based tty drivers.

See Also

ioctl(2), termios(3C), termio(4I), ldterm(4M)

HISTORY

Prior to Oracle Solaris 11.4, programs needed to push the ttcompat module onto the slave side of a pseudo-terminal pair if open() was called from a program not linked for XPG4 or later standards. If called from a program linked with values-xpg4.o or values-xpg6.o, then open() would automatically push ptem, ldterm, and ttcompat modules onto the slave side, and callers pushing them as well would encounter unexpected behavior.

Oracle Solaris 11.4 added these modules to /etc/iu.system.ap for pts(4D) so that they are automatically pushed by autopush(8) regardless of how the program is linked, and ensured that only one copy of each is pushed onto each stream.