RESTART_SYSCALL
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
restart_syscall - restart a system call after interruption by a stop signal
SYNOPSIS
int restart_syscall(void);
Note:
There is no glibc wrapper for this system call; see NOTES.
DESCRIPTION
The
restart_syscall()
system call is used to restart certain system calls
after a process that was stopped by a signal (e.g.,
SIGSTOP
or
SIGTSTP)
is later resumed after receiving a
SIGCONT
signal.
This system call is designed only for internal use by the kernel.
restart_syscall()
is used for restarting only those system calls that,
when restarted, should adjust their time-related parameters---namely
poll(2)
(since Linux 2.6.24),
nanosleep(2)
(since Linux 2.6),
clock_nanosleep(2)
(since Linux 2.6),
and
futex(2),
when employed with the
FUTEX_WAIT
(since Linux 2.6.22)
and
FUTEX_WAIT_BITSET
(since Linux 2.6.31)
operations.
restart_syscall()
restarts the interrupted system call with a
time argument that is suitably adjusted to account for the
time that has already elapsed (including the time where the process
was stopped by a signal).
Without the
restart_syscall()
mechanism, restarting these system calls would not correctly deduct the
already elapsed time when the process continued execution.
RETURN VALUE
The return value of
restart_syscall()
is the return value of whatever system call is being restarted.
ERRORS
errno
is set as per the errors for whatever system call is being restarted by
restart_syscall().
VERSIONS
The
restart_syscall()
system call is present since Linux 2.6.
CONFORMING TO
This system call is Linux-specific.
NOTES
There is no glibc wrapper for this system call,
because it is intended for use only by the kernel and
should never be called by applications.
The kernel uses
restart_syscall()
to ensure that when a system call is restarted
after a process has been stopped by a signal and then resumed by
SIGCONT,
then the time that the process spent in the stopped state is counted
against the timeout interval specified in the original system call.
In the case of system calls that take a timeout argument and
automatically restart after a stop signal plus
SIGCONT,
but which do not have the
restart_syscall()
mechanism built in, then, after the process resumes execution,
the time that the process spent in the stop state is
not
counted against the timeout value.
Notable examples of system calls that suffer this problem are
ppoll(2),
select(2),
and
pselect(2).
From user space, the operation of
restart_syscall()
is largely invisible:
to the process that made the system call that is restarted,
it appears as though that system call executed and
returned in the usual fashion.
SEE ALSO
sigaction(2),
sigreturn(2),
signal(7)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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