RESTART_SYSCALL(2)        (2020-12-21)         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) opera-
          tions.  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
          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().

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

     CONFORMING TO
          This system call is Linux-specific.

     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.

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     RESTART_SYSCALL(2)        (2020-12-21)         RESTART_SYSCALL(2)

          The kernel uses restart_syscall() to ensure that when a sys-
          tem 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
          sigaction(2), sigreturn(2), signal(7)

     COLOPHON
          This page is part of release 5.10 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 https://www.kernel.org/doc/man-pages/.

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