restart_syscall(2) - Linux manual page (original) (raw)

restartsyscall(2) System Calls Manual restartsyscall(2)

NAME top

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

SYNOPSIS top

   **long 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)](../man2/poll.2.html) (since Linux 2.6.24), [nanosleep(2)](../man2/nanosleep.2.html) (since Linux
   2.6), [clock_nanosleep(2)](../man2/clock%5Fnanosleep.2.html) (since Linux 2.6), and [futex(2)](../man2/futex.2.html), 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](../man3/errno.3.html)_ is set as per the errors for whatever system call is being
   restarted by **restart_syscall**().

STANDARDS top

   Linux.

HISTORY top

   Linux 2.6.

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
   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)](../man2/ppoll.2.html), [select(2)](../man2/select.2.html),
   and [pselect(2)](../man2/pselect.2.html).

   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)](../man2/sigaction.2.html), [sigreturn(2)](../man2/sigreturn.2.html), [signal(7)](../man7/signal.7.html)

COLOPHON top

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Linux man-pages 6.10 2024-05-02 restartsyscall(2)

Pages that refer to this page:lsfd(1), clock_nanosleep(2), futex(2), nanosleep(2), poll(2), ptrace(2), select(2), sigaction(2), sigreturn(2), syscalls(2), signal(7)