noble (2) restart_syscall.2.gz

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().

STANDARDS

       Linux.

HISTORY

       Linux 2.6.

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)