pty.7 (2010 09)

p
pty(7) pty(7)
trapping is enabled if the int addressed by arg is nonzero and disabled if the
int
addressed by arg is zero. By default,
TIOCMONITOR trapping is disabled. TIOCMONI-
TOR works in series with TIOCTTY; that is, the
TIOCMONITOR trapping must be
enabled and
TIOCTTY must be enabled for termio ioctl()
requests to be trapped by
TIOCMONITOR. TIOCMONITOR trapping can be enabled or disabled regardless of the
state of TIOCTTY.
When
TIOCTTY is disabled, termio ioctl() requests are not trapped by
TIOCMONI-
TOR. However, ioctl() requests are trapped by
TIOCTRAP if TIOCTTY is disabled
and
TIOCTRAP is enabled. TIOCTRAP trapping allows the master side server to modify
the parameters and return values of an ioctl()
request, whereas TIOCTMONITOR
trapping does not.
TIOCMONITOR trapping allows the server on the master side to know when characteris-
tics of the line discipline in the pty
are changed by an application on its slave side. The
mechanism for handshaking
termio requests trapped by TIOCMONITOR
is the same as
the mechanism described above for requests trapped by TIOCTRAP. (It is recommended
that
termio ioctl() requests be used on the master side to interrogate the configured
state of the line discipline in the pty
. This compensates for the window of time before
TIOCMONITOR is enabled, when termio ioctl() requests are not trapped.)
When using
select() on the master side of a pty, the "exceptional condition" refers to an
open(),
close(),orioctl() request pending on the slave side, while "ready for reading or writing" indicates
that the device can be read from or written to successfully.
Of the
ioctl() requests subject to being trapped, only one-per-pty can be handled at a time. This
means that when an application does a non-termio ioctl() request to the slave side, all other
ioctl() requests to the same pty slave side are blocked until the first one is handshaked back by the
master side. (ioctl() requests that are not trapped, such as termio when TIOCTTY is enabled and
TIOCMONITOR is disabled, are not blocked.) This permits the implementation of indivisible operations
by an ioctl() call on the slave side that is passed to the server process.
In summary, the following method of handling trapped
ioctl(), open(), and close() requests is
preferred:
1. Call
select(). This system call blocks the master side until a slave side
ioctl(),
open(),orclose() request is trapped.
2. Make
TIOCREQCHECK ioctl() request. This step returns information about a trapped
ioctl(), open(),orclose() request. If TIOCREQCHECK returns the external variable
errno error [EINVAL], loop back to the select() call.
3. Make
argget ioctl() request. This optional step is used if argget
is nonzero and the
server wants to do more than just reject the trapped slave
ioctl() request.
4. Make
argset ioctl() request. This optional step is done if argset
is nonzero and the
server wants to pass back a modified
ioctl() structure. It is done after the trapped
ioctl() request is processed via the server on the master side.
5. Set
errno_error and return_value. If the trapped request is an ioctl(), set
errno_error appropriately. If the appropriate value for errno_error is zero,
return_value must be set. If open error mode is enabled, set errno_error to a nonzero
value to return an error to a trapped open() request.
6. Make
TIOCREQSET ioctl() request. This step completes the trapped ioctl(), open(),
or close() request.
While a process is waiting in the slave side of the
pty for the server to complete a handshake, it is sus-
ceptible to receiving signals. The following master side ioctl() request allows the server process to
control how the pty responds when a signal attempts to interrupt a trapped open() or ioctl()
request:
TIOCSIGMODE
Set the signal handling state of the pty to the mode specified as the argument. The
mode can have three values, which are TIOCSIGBLOCK, TIOCSIGABORT, and TIOC-
SIGNORMAL.
TIOCSIGBLOCK
Cause some signals to be postponed that are destined for the slave-side process
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