Note: There is no glibc wrapper for this system call; see NOTES.
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 sys-
tem 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 deduce the already
elapsed time when the process continued execution.
The return value of restart_syscall() is the return value of whatever
system call is being restarted.
errno is set as per the errors for whatever system call is being
restarted by restart_syscall().
The 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.
From user space, the operation of restart_syscall(2) is largely invisi-
ble: to the process that made the system call that is restarted, it
appears as though that system call executed and returned in the usual
sigreturn(2), sigaction(2), signal(7)
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