restart_syscall

RESTART_SYSCALL(2)          Linux Programmer's Manual         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) 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
       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.

       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
       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/.



Linux                              2020-12-21                 RESTART_SYSCALL(2)