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

NAME

       restart_syscall - restart a system call after interruption by a stop signal

SYNOPSIS

       int 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 applica-
       tions.

       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 4.15 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                                                               2017-09-15                                                  RESTART_SYSCALL(2)