X-Git-Url: http://git.osdn.net/view?p=linuxjm%2FLDP_man-pages.git;a=blobdiff_plain;f=original%2Fman2%2Frestart_syscall.2;h=f27555a1212b315fdb5494b70d31881608a31868;hp=b0c09eefd3f4bc2b6d71cf3350ffafd3a518b828;hb=4ea6bb24817f6f049d6bbc90ecd77a869876f9b0;hpb=71bb2920a65c5c30552c13bc5bf95fa86af82a56

diff --git a/original/man2/restart_syscall.2 b/original/man2/restart_syscall.2
index b0c09eef..f27555a1 100644
--- a/original/man2/restart_syscall.2
+++ b/original/man2/restart_syscall.2
@@ -30,7 +30,7 @@
 .\"
 .\" See also Section 11.3.3 of Understanding the Linux Kernel, 3rd edition
 .\"
-.TH RESTART_SYSCALL 2 2014-02-11 "Linux" "Linux Programmer's Manual"
+.TH RESTART_SYSCALL 2 2014-12-31 "Linux" "Linux Programmer's Manual"
 .SH NAME
 restart_syscall \- restart a system call after interruption by a stop signal
 .SH SYNOPSIS
@@ -72,6 +72,10 @@ operations.
 .\" These system calls correspond to the special internal errno value
 .\" ERESTART_RESTARTBLOCK. Each of the system calls has a "restart"
 .\" helper function that is invoked by restart_syscall().
+.\" Notable (as at Linux 3.17) is that poll() has such a "restart"
+.\" function, but ppoll(), select(), and pselect() do not.
+.\" This means that the latter system calls do not take account of the
+.\" time spent in the stopped state when restarting.
 .BR restart_syscall ()
 restarts the interrupted system call with a
 time argument that is suitably adjusted to account for the
@@ -79,7 +83,7 @@ time that has already elapsed (including the time where the process
 was stopped by a signal).
 Without the
 .BR restart_syscall ()
-mechanism, restarting these system calls would not correctly deduce the
+mechanism, restarting these system calls would not correctly deduct the
 already elapsed time when the process continued execution.
 .SH RETURN VALUE
 The return value of
@@ -100,31 +104,49 @@ 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
+.BR restart_syscall ()
+to ensure that when a system call is restarted
+after a process has been stopped by a signal and then resumed by
+.BR 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
+.BR SIGCONT ,
+but which do not have the
+.BR restart_syscall (2)
+mechanism built in, then, after the process resumes execution,
+the time that the process spent in the stop state is
+.I not
+counted against the timeout value.
+Notable examples of system calls that suffer this problem are
+.BR ppoll (2),
+.BR select (2),
+and
+.BR pselect (2).
+
 From user space, the operation of
 .BR restart_syscall (2)
 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.
-.\"
-.\" FIXME
-.\" There is one oddness in the implementation though, with respect to
-.\" nanosleep() (and probably also clock_nanosleep()). The scenario
-.\" is as follows:
-.\"    1. Start a nanosleep() for (say) 30 seconds,
-.\"    2. Stop the process with (say) SIGTSTP (^Z).
-.\"    3. Resume the process with SIGCONT,
-.\"    4. Upon return, the 'rem' argument of nanosleep() will contain the
-.\"       remaining unslept time **at the time when SIGTSTP was delivered**.
-.\" The behavior at point 4 is odd, but doesn't violate the standards, which
-.\" specify the treatment of 'rem' only when the system call returns with
-.\" the error EINTR (i.e., the call was interrupted by a signal handler).
-.\"
 .SH SEE ALSO
 .BR sigaction (2),
 .BR sigreturn (2),
 .BR signal (7)
-.\" FIXME select(2) should probably get the restart_syscall() treatment:
+.\" FIXME . ppoll(2), select(2), and pselect(2)
+.\"     should probably get the restart_syscall() treatment:
 .\"     If a select() call is suspended by stop-sig+SIGCONT, the time
 .\"     spent suspended is *not* deducted when the select() is restarted.
-.\" FIXME: check whether recvmmsg() handles stop-sig+SIGCONT properly.
+.\" FIXME . check whether recvmmsg() handles stop-sig+SIGCONT properly.
+.SH COLOPHON
+This page is part of release 3.79 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.