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Diffstat (limited to 'manual/terminal.texi')
| -rw-r--r-- | manual/terminal.texi | 289 |
1 files changed, 271 insertions, 18 deletions
diff --git a/manual/terminal.texi b/manual/terminal.texi index 4e4be88..e6dc36d 100644 --- a/manual/terminal.texi +++ b/manual/terminal.texi @@ -22,6 +22,7 @@ descriptor is and how to open a file descriptor for a terminal device. * Line Control:: Sending break sequences, clearing terminal buffers @dots{} * Noncanon Example:: How to read single characters without echo. +* Pseudo-Terminals:: How to open a pseudo-terminal. @end menu @node Is It a Terminal @@ -35,14 +36,14 @@ descriptor is associated with a terminal by using the @code{isatty} function. @pindex unistd.h -Prototypes for both @code{isatty} and @code{ttyname} are declared in -the header file @file{unistd.h}. +Prototypes for the functions in this section are declared in the header +file @file{unistd.h}. @comment unistd.h @comment POSIX.1 @deftypefun int isatty (int @var{filedes}) This function returns @code{1} if @var{filedes} is a file descriptor -associated with an open terminal device, and @code{0} otherwise. +associated with an open terminal device, and @math{0} otherwise. @end deftypefun If a file descriptor is associated with a terminal, you can get its @@ -59,6 +60,30 @@ the terminal file. The value is a null pointer if the file descriptor isn't associated with a terminal, or the file name cannot be determined. @end deftypefun +@comment unistd.h +@comment POSIX.1 +@deftypefun int ttyname_r (int @var{filedes}, char *@var{buf}, size_t @var{len}) +The @code{ttyname_r} function is similar to the @code{ttyname} function +except that it places its result into the user-specified buffer starting +at @var{buf} with length @var{len}. + +The normal return value from @code{ttyname_r} is @math{0}. Otherwise an +error number is returned to indicate the error. The following +@code{errno} error conditions are defined for this function: + +@table @code +@item EBADF +The @var{filedes} argument is not a valid file descriptor. + +@item ENOTTY +The @var{filedes} is not associated with a terminal. + +@item ERANGE +The buffer length @var{len} is too small to store the string to be +returned. +@end table +@end deftypefun + @node I/O Queues @section I/O Queues @@ -237,7 +262,7 @@ This function is used to examine the attributes of the terminal device with file descriptor @var{filedes}. The attributes are returned in the structure that @var{termios-p} points to. -If successful, @code{tcgetattr} returns @code{0}. A return value of @code{-1} +If successful, @code{tcgetattr} returns @math{0}. A return value of @math{-1} indicates an error. The following @code{errno} error conditions are defined for this function: @@ -302,8 +327,8 @@ write to the terminal. The exception is if the calling process itself is ignoring or blocking @code{SIGTTOU} signals, in which case the operation is performed and no signal is sent. @xref{Job Control}. -If successful, @code{tcsetattr} returns @code{0}. A return value of -@code{-1} indicates an error. The following @code{errno} error +If successful, @code{tcsetattr} returns @math{0}. A return value of +@math{-1} indicates an error. The following @code{errno} error conditions are defined for this function: @table @code @@ -997,27 +1022,27 @@ This function returns the input line speed stored in the structure @comment POSIX.1 @deftypefun int cfsetospeed (struct termios *@var{termios-p}, speed_t @var{speed}) This function stores @var{speed} in @code{*@var{termios-p}} as the output -speed. The normal return value is @code{0}; a value of @code{-1} +speed. The normal return value is @math{0}; a value of @math{-1} indicates an error. If @var{speed} is not a speed, @code{cfsetospeed} -returns @code{-1}. +returns @math{-1}. @end deftypefun @comment termios.h @comment POSIX.1 @deftypefun int cfsetispeed (struct termios *@var{termios-p}, speed_t @var{speed}) This function stores @var{speed} in @code{*@var{termios-p}} as the input -speed. The normal return value is @code{0}; a value of @code{-1} +speed. The normal return value is @math{0}; a value of @math{-1} indicates an error. If @var{speed} is not a speed, @code{cfsetospeed} -returns @code{-1}. +returns @math{-1}. @end deftypefun @comment termios.h @comment BSD @deftypefun int cfsetspeed (struct termios *@var{termios-p}, speed_t @var{speed}) This function stores @var{speed} in @code{*@var{termios-p}} as both the -input and output speeds. The normal return value is @code{0}; a value -of @code{-1} indicates an error. If @var{speed} is not a speed, -@code{cfsetspeed} returns @code{-1}. This function is an extension in +input and output speeds. The normal return value is @math{0}; a value +of @math{-1} indicates an error. If @var{speed} is not a speed, +@code{cfsetspeed} returns @math{-1}. This function is an extension in 4.4 BSD. @end deftypefun @@ -1035,7 +1060,7 @@ will succeed. But they do not check that a particular hardware device can actually support the specified speeds---in fact, they don't know which device you plan to set the speed for. If you use @code{tcsetattr} to set the speed of a particular device to a value that it cannot -handle, @code{tcsetattr} returns @code{-1}. +handle, @code{tcsetattr} returns @math{-1}. @strong{Portability note:} In the GNU library, the functions above accept speeds measured in bits per second as input, and return speed @@ -1629,7 +1654,7 @@ This function does nothing if the terminal is not an asynchronous serial data port. The return value is normally zero. In the event of an error, a value -of @code{-1} is returned. The following @code{errno} error conditions +of @math{-1} is returned. The following @code{errno} error conditions are defined for this function: @table @code @@ -1659,7 +1684,7 @@ protected using cancelation handlers. @c ref pthread_cleanup_push / pthread_cleanup_pop The return value is normally zero. In the event of an error, a value -of @code{-1} is returned. The following @code{errno} error conditions +of @math{-1} is returned. The following @code{errno} error conditions are defined for this function: @table @code @@ -1705,7 +1730,7 @@ Clear both queued input and output. @end table The return value is normally zero. In the event of an error, a value -of @code{-1} is returned. The following @code{errno} error conditions +of @math{-1} is returned. The following @code{errno} error conditions are defined for this function: @table @code @@ -1759,7 +1784,7 @@ For more information about the STOP and START characters, see @ref{Special Characters}. The return value is normally zero. In the event of an error, a value -of @code{-1} is returned. The following @code{errno} error conditions +of @math{-1} is returned. The following @code{errno} error conditions are defined for this function: @table @code @@ -1805,3 +1830,231 @@ a process is stopped or continued; see @ref{Job Control}. But some existing shells do not actually do this, so you may wish to establish handlers for job control signals that reset terminal modes. The above example does so. + + +@node Pseudo-Terminals +@section Pseudo-Terminals +@cindex pseudo-terminals + +A @dfn{pseudo-terminal} is a special interprocess communication channel +that acts like a terminal. On one end of the channel is called the +@dfn{master} side or @dfn{master pseudo-terminal device}, the other side +is called the @dfn{slave} side. Data written to the the master side is +received by the slave side as if it was the result of a user typing at +an ordinary terminal, and data written to the slave side is sent to the +master side as if it was written on an ordinary terminal. + +Pseudo terminals are the way programs like @code{xterm} and @code{emacs} +implement their terminal emulation functionality. + +@menu +* Allocation:: Allocating a pseudo terminal. +* Pseudo-Terminal Pairs:: How to open both sides of a + pseudo-terminal in a single operation. +@end menu + +@node Allocation +@subsection Allocating Pseudo-Terminals +@cindex allocating pseudo-terminals + +@pindex stdlib.h +This subsection describes functions for allocating a pseudo-terminals, +and for making this pseudo-terminal available for actual use. These +functions are declared in the header file @file{stdlib.h}. + +@comment stdlib.h +@comment GNU +@deftypefun int getpt (void) +The @code{getpt} function returns a new file descriptor for the next +available master pseudo-terminal. The normal return value from +@code{getpt} is a non-negative integer file descriptor. In the case of +an error, a value of @math{-1} is returned instead. The following +@code{errno} conditions are defined for this function: + +@table @code +@item ENFILE +There are no master pseudo-terminals available. +@end table + +This function is a GNU extension. +@end deftypefun + +@comment stdlib.h +@comment SVID, XPG4.2 +@deftypefun int grantpt (int @var{filedes}) +The @code{grantpt} function changes the ownership and access permission +of the slave pseudo-terminal device corresponding to the master +pseudo-terminal device associated with the file descriptor +@var{filedes}. The owner is set from the real user ID of the calling +process (@pxref{Process Persona}), and the group is set to a special +group (typically @dfn{tty}) or from the real group ID of the calling +process. The access permission is set such that the file is both +readable and writable by the owner and only writable by the group. + +On some systems this function is implemented by invoking a special +@code{setuid} root program (@pxref{How Change Persona}). As a +consequence, installing a signal handler for the @code{SIGCHLD} signal +(@pxref{Job Control Signals}) may interfere with a call to +@code{grantpt}. + +The normal return value from @code{grantpt} is @math{0}; a value of +@math{-1} is returned in case of failure. The following @code{errno} +error conditions are defined for this function: + +@table @code +@item EBADF +The @var{filedes} argument is not a valid file descriptor. + +@item ENINVAL +The @var{filedes} argument is not associated with a master pseudo-terminal +device. + +@item EACCESS +The slave pseudo-terminal device corresponding to the master associated +with @var{filedes} could not be accessed. +@end table + +@end deftypefun + +@comment stdlib.h +@comment SVID, XPG4.2 +@deftypefun int unlockpt (int @var{filedes}) +The @code{unlockpt} function unlocks the slave pseudo-terminal device +corresponding to the master pseudo-terminal device associated with the +file descriptor @var{filedes}. On many systems, the slave can only be +opened after unlocking, so portable applications should always call +@code{unlockpt} before trying to open the slave. + +The normal return value from @code{unlockpt} is @math{0}; a value of +@math{-1} is returned in case of failure. The following @code{errno} +error conditions are defined for this function: + +@table @code +@item EBADF +The @var{filedes} argument is not a valid file descriptor. + +@item EINVAL +The @var{filedes} argument is not associated with a master pseudo-terminal +device. +@end table +@end deftypefun + +@comment stdlib.h +@comment SVID, XPG4.2 +@deftypefun {char *} ptsname (int @var{filedes}) +If the file descriptor @var{filedes} is associated with a +master pseudo-terminal device, the @code{ptsname} function returns a +pointer to a statically-allocated, null-terminated string containing the +file name of the associated slave pseudo-terminal file. This string +might be overwritten by subsequent calls to @code{ptsname}. +@end deftypefun + +@comment stdlib.h +@comment GNU +@deftypefun int ptsname_r (int @var{filedes}, char *@var{buf}, size_t @var{len}) +The @code{ptsname_r} function is similar to the @code{ptsname} function +except that it places its result into the user-specified buffer starting +at @var{buf} with length @var{len}. + +This function is a GNU extension. +@end deftypefun + +@strong{Portability Note:} On @w{System V} derived systems, the file +returned by the @code{ptsname} and @code{ptsname_r} functions may be +STREAMS-based, and therefore require additional processing after opening +before it actually behaves as a pseudo terminal. +@c FIXME: xref STREAMS + +Typical usage of these functions is illustrated by the following example: +@smallexample +int +open_pty_pair (int *amaster, int *aslave) +@{ + int master, slave; + char *name + + master = getpt (); + if (master < 0) + return 0; + + if (grantpt (master) < 0 || unlockpt (master) < 0) + goto close_master; + name = ptsname (master); + if (name == NULL) + goto close_master; + + slave open (name, O_RDWR); + if (slave == -1) + goto close_master; + + if (isastream (slave)) + @{ + if (ioctl (slave, I_PUSH, "ptem") < 0 + || ioctl (slave, I_PUSH, "ldterm") < 0) + goto close_slave; + @} + + *amaster = master; + *aslave = slave; + return 1; + +close_slave: + close (slave); + +close_master: + close (master); + return 0; +@} +@end smallexample + +@node Pseudo-Terminal Pairs +@subsection Opening a Pseudo-Terminal Pair +@cindex opening a pseudo-terminal pair + +These functions, derived from BSD, are available in the separate +@file{libutil} library, and declared in @file{pty.h}. + +@comment pty.h +@comment BSD +@deftypefun int openpty (int *@var{amaster}, int *@var{aslave}, char *@var{name}, struct termios *@var{termp}, struct winsize *@var{winp}) +This function allocates and opens a pseudo-terminal pair, returning the +file descriptor for the master in @var{*amaster}, and the file +descriptor for the slave in @var{*aslave}. If the argument @var{name} +is not a null pointer, the name file name of the slave pseudo-terminal +device is stored in @code{*name}. If @var{termp} is not a null pointer, +the terminal attributes of the slave are set to the ones specified in +the structure that @var{termp} points to (@pxref{Terminal Modes}). +Likewise, if the @var{winp} is not a null pointer, the screen size of +the slave is set to the values specified in the structure that +@var{winp} points to. + +The normal return value from @code{openpty} is @math{0}; a value of +@math{-1} is returned in case of failure. + +@strong{Warning:} Using the @code{openpty} with @var{name} not set to +@code{NULL} is @strong{very dangerous} because it provides no protection +against overflowing the string @var{name}. You should use the +@code{ttyname} function on the file descriptor returned in @var{*slave} +to find out the file name of the slave pseudo-terminal device instead. +@end deftypefun + +@comment pty.h +@comment BSD +@deftypefun int forkpty (int *@var{amaster}, char *@var{name}, struct termios *@var{termp}, struct winsize *@var{winp}) +This function is similar to the @code{openpty} function, but in +addition, forks creates a new process (@pxref{Creating a Process}) and +makes the newly opened slave pseudo-terminal device the controlling +terminal (@pxref{Controlling Terminal}) for the child process. + +If the operation is successful, there are then both parent and child +processes and both see @code{forkpty} return, but with different values: +it returns a value of @math{0} in the child process and returns the child's +process ID in the parent process. + +If the allocation of a pseudo-terminal pair or the process creation +failed, @code{forkpty} returns a value of @math{-1} in the parent +process. + +@strong{Warning:} The @code{forkpty} function has the same problems with +respect to the @var{name} argument as @code{openpty}. +@end deftypefun |