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       restart_syscall  -  restart  a system call after interruption by a stop


       int restart_syscall(void);

       Note: There is no glibc wrapper for this system call; see NOTES.


       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.


       The  return  value of restart_syscall() is the return value of whatever
       system call is being restarted.


       errno is set as per the  errors  for  whatever  system  call  is  being
       restarted by restart_syscall().


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


       This system call is Linux-specific.


       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(2) 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

       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.


       sigaction(2), sigreturn(2), signal(7)


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