From 399644e47874bff147afb19c89228901ac39340e Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 15 Apr 2024 21:40:15 +0200 Subject: Adding upstream version 6.05.01. Signed-off-by: Daniel Baumann --- man2/restart_syscall.2 | 123 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 123 insertions(+) create mode 100644 man2/restart_syscall.2 (limited to 'man2/restart_syscall.2') diff --git a/man2/restart_syscall.2 b/man2/restart_syscall.2 new file mode 100644 index 0000000..4b0e101 --- /dev/null +++ b/man2/restart_syscall.2 @@ -0,0 +1,123 @@ +.\" Copyright (c) 2013 by Michael Kerrisk +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" http://thread.gmane.org/gmane.linux.kernel/76552/focus=76803 +.\" From: Linus Torvalds transmeta.com> +.\" Subject: Re: [PATCH] compatibility syscall layer (lets try again) +.\" Newsgroups: gmane.linux.kernel +.\" Date: 2002-12-05 02:51:12 GMT +.\" +.\" See also Section 11.3.3 of Understanding the Linux Kernel, 3rd edition +.\" +.TH restart_syscall 2 2023-03-30 "Linux man-pages 6.05.01" +.SH NAME +restart_syscall \- restart a system call after interruption by a stop signal +.SH SYNOPSIS +.nf +.B long restart_syscall(void); +.fi +.PP +.IR Note : +There is no glibc wrapper for this system call; see NOTES. +.SH DESCRIPTION +The +.BR restart_syscall () +system call is used to restart certain system calls +after a process that was stopped by a signal (e.g., +.B SIGSTOP +or +.BR SIGTSTP ) +is later resumed after receiving a +.B SIGCONT +signal. +This system call is designed only for internal use by the kernel. +.PP +.BR restart_syscall () +is used for restarting only those system calls that, +when restarted, should adjust their time-related parameters\[em]namely +.BR poll (2) +(since Linux 2.6.24), +.BR nanosleep (2) +(since Linux 2.6), +.BR clock_nanosleep (2) +(since Linux 2.6), +and +.BR futex (2), +when employed with the +.B FUTEX_WAIT +(since Linux 2.6.22) +and +.B FUTEX_WAIT_BITSET +(since Linux 2.6.31) +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 +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 deduct the +already elapsed time when the process continued execution. +.SH RETURN VALUE +The return value of +.BR restart_syscall () +is the return value of whatever system call is being restarted. +.SH ERRORS +.I errno +is set as per the errors for whatever system call is being restarted by +.BR restart_syscall (). +.SH STANDARDS +Linux. +.SH HISTORY +Linux 2.6. +.SH 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. +.PP +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 () +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). +.PP +From user space, the operation of +.BR 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. +.SH SEE ALSO +.BR sigaction (2), +.BR sigreturn (2), +.BR signal (7) +.\" 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. -- cgit v1.2.3