LDP: Update original to LDP v3.68

[linuxjm/LDP_man-pages.git] / original / man2 / read.2

diff --git a/original/man2/read.2 b/original/man2/read.2
index ed318e4..2a9dcdb 100644 (file)
--- a/original/man2/read.2
+++ b/original/man2/read.2
@@ -32,7 +32,7 @@
 .\" Modified Sat Jul 12 20:45:39 1997 by Michael Haardt
 .\"   <michael@cantor.informatik.rwth-aachen.de>
 .\"
-.TH READ 2 2013-02-12 "Linux" "Linux Programmer's Manual"
+.TH READ 2 2014-05-04 "Linux" "Linux Programmer's Manual"
 .SH NAME
 read \- read from a file descriptor
 .SH SYNOPSIS
@@ -90,7 +90,7 @@ was interrupted by a signal.
 On error, \-1 is returned, and
 .I errno
 is set appropriately.
-In this case it is left unspecified whether
+In this case, it is left unspecified whether
 the file position (if any) changes.
 .SH ERRORS
 .TP
@@ -173,7 +173,7 @@ or to return the number of bytes already read.
 .SH CONFORMING TO
 SVr4, 4.3BSD, POSIX.1-2001.
 .SH NOTES
-On NFS file systems, reading small amounts of data will update the
+On NFS filesystems, reading small amounts of data will update the
 timestamp only the first time, subsequent calls may not do so.
 This is caused
 by client side attribute caching, because most if not all NFS clients
@@ -184,6 +184,45 @@ server side reads.
 UNIX semantics can be obtained by disabling client
 side attribute caching, but in most situations this will substantially
 increase server load and decrease performance.
+.SH BUGS
+According to POSIX.1-2008/SUSv4 Section XSI 2.9.7
+("Thread Interactions with Regular File Operations"):
+
+.RS 4
+All of the following functions shall be atomic with respect to
+each other in the effects specified in POSIX.1-2008 when they
+operate on regular files or symbolic links: ...
+.RE
+
+Among the APIs subsequently listed are
+.BR read ()
+and
+.BR readv (2).
+And among the effects that should be atomic across threads (and processes)
+are updates of the file offset.
+However, on Linux before version 3.14,
+this was not the case: if two processes that share
+an open file description (see
+.BR open (2))
+perform a
+.BR read ()
+(or
+.BR readv (2))
+at the same time, then the I/O operations were not atomic
+with respect updating the file offset,
+with the result that the reads in the two processes
+might (incorrectly) overlap in the blocks of data that they obtained.
+This problem was fixed in Linux 3.14.
+.\" http://thread.gmane.org/gmane.linux.kernel/1649458
+.\"    From: Michael Kerrisk (man-pages <mtk.manpages <at> gmail.com>
+.\"    Subject: Update of file offset on write() etc. is non-atomic with I/O
+.\"    Date: 2014-02-17 15:41:37 GMT
+.\"    Newsgroups: gmane.linux.kernel, gmane.linux.file-systems
+.\" commit 9c225f2655e36a470c4f58dbbc99244c5fc7f2d4
+.\"    Author: Linus Torvalds <torvalds@linux-foundation.org>
+.\"    Date:   Mon Mar 3 09:36:58 2014 -0800
+.\"
+.\"        vfs: atomic f_pos accesses as per POSIX
 .SH SEE ALSO
 .BR close (2),
 .BR fcntl (2),
@@ -197,3 +236,12 @@ increase server load and decrease performance.
 .BR select (2),
 .BR write (2),
 .BR fread (3)
+.SH COLOPHON
+This page is part of release 3.68 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/.