restart_syscall(2) System Calls Manual restart_syscall(2)
NAME
restart_syscall - restart a system call after interruption by a stop
signal
SYNOPSIS
long 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, restart-
ing 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().
STANDARDS
Linux.
HISTORY
Linux 2.6.
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 au-
tomatically 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 invisi-
ble: to the process that made the system call that is restarted, it ap-
pears as though that system call executed and returned in the usual
fashion.
SEE ALSO
sigaction(2), sigreturn(2), signal(7)
Linux man-pages 6.9.1 2024-05-02 restart_syscall(2)
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