restart_syscall(2) — Linux manual page


RESTART_SYSCALL(2)        Linux Programmer's Manual       RESTART_SYSCALL(2)

NAME         top

       restart_syscall  - restart a system call after interruption by a stop

SYNOPSIS         top

       int restart_syscall(void);

       Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION         top

       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         top

       The return value of restart_syscall() is the return value of whatever
       system call is being restarted.

ERRORS         top

       errno is set as per the errors for whatever system call is being
       restarted by restart_syscall().

VERSIONS         top

       The restart_syscall() system call is present since Linux 2.6.

CONFORMING TO         top

       This system call is Linux-specific.

NOTES         top

       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

       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         top

       sigaction(2), sigreturn(2), signal(7)

COLOPHON         top

       This page is part of release 5.09 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

Linux                            2017-09-15               RESTART_SYSCALL(2)

Pages that refer to this page: clock_nanosleep(2)futex(2)nanosleep(2)_newselect(2)poll(2)ppoll(2)pselect(2)pselect6(2)ptrace(2)rt_sigaction(2)rt_sigreturn(2)select(2)sigaction(2)sigreturn(2)syscalls(2)fd_clr(3)FD_CLR(3)fd_isset(3)FD_ISSET(3)fd_set(3)FD_SET(3)fd_zero(3)FD_ZERO(3)signal(7)