restart_syscall - restart a system call after interruption by a stop signal
Note: There is no glibc wrapper for this system call; see
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.
The return value of restart_syscall() is the return value of whatever system call is being restarted.
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 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
not counted against the timeout value. Notable
examples of system calls that suffer this problem are
ppoll(2), select(2), and
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.
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