restart_syscall - restart a system call after interruption by a stop signal
: There is no glibc wrapper for this system call; see NOTES.
() system call is used to restart certain system calls
after a process that was stopped by a signal (e.g., SIGSTOP
) is later resumed after receiving a SIGCONT
system call is designed only for internal use by the kernel.
() is used for restarting only those system calls that,
when restarted, should adjust their time-related parameters—namely
(2) (since Linux 2.6.24), nanosleep
(2) (since Linux 2.6),
(2) (since Linux 2.6), and futex
employed with the FUTEX_WAIT
(since Linux 2.6.22) and
(since Linux 2.6.31) operations.
() 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
The return value of restart_syscall
() is the return value of whatever
system call is being restarted.
is set as per the errors for whatever system call is being
restarted by restart_syscall
() system call is present since Linux 2.6.
This system call is Linux-specific.
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
, 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
() 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
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.