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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2007-09-10 04:34:20 +0000 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2007-09-10 04:34:20 +0000 |
| commit | fe75ec04d3374649d8f86eb92447795afae988a1 (patch) | |
| tree | 92774d8a482a0326152f5aae97349a74c274ed82 /man2 | |
| parent | d739f5f8c71e6b173c75a806fb47110b4dcb61a9 (diff) | |
| download | man-pages-fe75ec04d3374649d8f86eb92447795afae988a1.tar.gz | |
Added description of O_CLOEXEC (new in 2.6.23) + other
minor fixes for O_DIRECT.
Diffstat (limited to 'man2')
| -rw-r--r-- | man2/open.2 | 49 |
1 files changed, 40 insertions, 9 deletions
diff --git a/man2/open.2 b/man2/open.2 index 3a89d5df3d..d4d7955288 100644 --- a/man2/open.2 +++ b/man2/open.2 @@ -35,8 +35,9 @@ .\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net> .\" 2004-12-08, mtk, reordered flags list alphabetically .\" 2004-12-08, Martin Pool <mbp@sourcefrog.net> (& mtk), added O_NOATIME +.\" 2007-09-18, mtk, Added description of O_CLOEXEC + other minor edits .\" -.TH OPEN 2 2005-06-22 "Linux" "Linux Programmer's Manual" +.TH OPEN 2 2007-09-18 "Linux" "Linux Programmer's Manual" .SH NAME open, creat \- open and possibly create a file or device .SH SYNOPSIS @@ -60,13 +61,15 @@ for use in subsequent system calls The file descriptor returned by a successful call will be the lowest-numbered file descriptor not currently open for the process. .PP -The new file descriptor is set to remain open across an +By default, the new file descriptor is set to remain open across an .BR execve (2) (i.e., the .B FD_CLOEXEC file descriptor flag described in .BR fcntl (2) -is initially disabled). +is initially disabled; the Linux-specific +.B O_CLOEXEC +flag, described below, can be used to change this default). The file offset is set to the beginning of the file (see .BR lseek (2)). .PP @@ -141,7 +144,31 @@ sockets, and (since Linux 2.6) pipes and FIFOs. See .BR fcntl (2) for further details. -.\" FIXME 2.6.23 adds O_CLOEXEC -- this needs to be documented +.TP +.BR O_CLOEXEC " (Since Linux 2.6.23)" +Enable the close-on-exec flag for the new file descriptor. +Specifying this flag permits a program to avoid an additional +.BR fcntl (2) +.B F_SETFD +operation to set the +.BR FD_CLOEXEC +flag. +Additionally, +use of this flag is essential in some multithreaded programs +since using a separate +.BR fcntl (2) +.B F_SETFD +operation to set the +.BR FD_CLOEXEC +flag does not suffice to avoid race conditions +where one thread opens a file descriptor at the same +time as another thread does a +.BR fork (2) +plus +.BR execve (2). +.\" This flag fixes only one form of the race condition; +.\" The race can also occur with, for example, descriptors +.\" returned by accept(), pipe(), etc. .TP .B O_CREAT If the file does not exist it will be created. @@ -157,7 +184,7 @@ and of the ext2 filesystem, as described in .BR mount (8)). .TP -.B O_DIRECT +.BR O_DIRECT " (Since Linux 2.6.10)" Try to minimize cache effects of the I/O to and from this file. In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. @@ -236,8 +263,7 @@ is the preferred method of obtaining method of accessing large files on 32-bit systems (see .BR feature_test_macros (7)). .TP -.B O_NOATIME -(Since Linux 2.6.8) +.BR O_NOATIME " (Since Linux 2.6.8)" Do not update the file last access time (st_atime in the inode) when the file is .BR read (2). @@ -502,14 +528,19 @@ flag was specified, and an incompatible lease was held on the file .SH "CONFORMING TO" SVr4, 4.3BSD, POSIX.1-2001. The +.BR O_CLOEXEC , +.BR O_DIRECTORY , .BR O_NOATIME , -.BR O_NOFOLLOW , and -.B O_DIRECTORY +.BR O_NOFOLLOW flags are Linux specific. One may have to define the .B _GNU_SOURCE macro to get their definitions. +.BR O_DIRECT +is not specified in POSIX; one has to define +.B _GNU_SOURCE +to get its definition. .SH NOTES Under Linux, the .B O_NONBLOCK |