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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2014-03-16 10:02:33 +0100 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2014-03-17 08:46:40 +0100 |
| commit | 5dc8986d0daaeba17a891f4d04b61be5395f23f1 (patch) | |
| tree | 2893ccc318a40e2758ee8dac9797c6aa502c5fee /man2/open.2 | |
| parent | 3b7aa6b1165812ac717c7d2d903785961435db53 (diff) | |
| download | man-pages-5dc8986d0daaeba17a891f4d04b61be5395f23f1.tar.gz | |
open.2: Organize some material under additional subheadings in NOTES
There's an amorphous mass of material under NOTES. Structure
it with some subheadings, and do a little reorganizing.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man2/open.2')
| -rw-r--r-- | man2/open.2 | 126 |
1 files changed, 67 insertions, 59 deletions
diff --git a/man2/open.2 b/man2/open.2 index d1808a0461..2ab3e88cb6 100644 --- a/man2/open.2 +++ b/man2/open.2 @@ -693,7 +693,7 @@ except for the differences described here. If the pathname given in .I pathname is relative, then it is interpreted relative to the directory -referred to by the file descriptor + to by the file descriptor .I dirfd (rather than relative to the current working directory of the calling process, as is done by @@ -1002,34 +1002,6 @@ This is typically used to open devices in order to get a file descriptor for use with .BR ioctl (2). -Unlike the other values that can be specified in -.IR flags , -the -.I "access mode" -values -.BR O_RDONLY ", " O_WRONLY ", and " O_RDWR -do not specify individual bits. -Rather, they define the low order two bits of -.IR flags , -and are defined respectively as 0, 1, and 2. -In other words, the combination -.B "O_RDONLY | O_WRONLY" -is a logical error, and certainly does not have the same meaning as -.BR O_RDWR . -Linux reserves the special, nonstandard access mode 3 (binary 11) in -.I flags -to mean: -check for read and write permission on the file and return a descriptor -that can't be used for reading or writing. -This nonstandard access mode is used by some Linux drivers to return a -descriptor that is to be used only for device-specific -.BR ioctl (2) -operations. -.\" See for example util-linux's disk-utils/setfdprm.c -.\" For some background on access mode 3, see -.\" http://thread.gmane.org/gmane.linux.kernel/653123 -.\" "[RFC] correct flags to f_mode conversion in __dentry_open" -.\" LKML, 12 Mar 2008 .LP The (undefined) effect of .B O_RDONLY | O_TRUNC @@ -1041,11 +1013,36 @@ On many systems the file is actually truncated. .\" Tru64 5.1B: truncate .\" HP-UX 11.22: truncate .\" FreeBSD 4.7: truncate -.PP -There are many infelicities in the protocol underlying NFS, affecting -amongst others -.BR O_SYNC " and " O_NDELAY . +Note that +.BR open () +can open device special files, but +.BR creat () +cannot create them; use +.BR mknod (2) +instead. + +If the file is newly created, its +.IR st_atime , +.IR st_ctime , +.I st_mtime +fields +(respectively, time of last access, time of last status change, and +time of last modification; see +.BR stat (2)) +are set +to the current time, and so are the +.I st_ctime +and +.I st_mtime +fields of the +parent directory. +Otherwise, if the file is modified because of the +.B O_TRUNC +flag, its st_ctime and st_mtime fields are set to the current time. +.\" +.\" +.SS Synchronized I/O POSIX provides for three different variants of synchronized I/O, corresponding to the flags .BR O_SYNC , @@ -1067,15 +1064,13 @@ to be on disk on returning to user space, but only the .B O_DSYNC semantics, which require only actual file data and metadata necessary to retrieve it to be on disk by the time the system call returns. +.\" +.\" +.SS NFS +There are many infelicities in the protocol underlying NFS, affecting +amongst others +.BR O_SYNC " and " O_NDELAY . -Note that -.BR open () -can open device special files, but -.BR creat () -cannot create them; use -.BR mknod (2) -instead. -.LP On NFS filesystems with UID mapping enabled, .BR open () may @@ -1088,25 +1083,38 @@ This is because the client performs by checking the permissions, but UID mapping is performed by the server upon read and write requests. +.\" +.\" +.SS File access mode +Unlike the other values that can be specified in +.IR flags , +the +.I "access mode" +values +.BR O_RDONLY ", " O_WRONLY ", and " O_RDWR +do not specify individual bits. +Rather, they define the low order two bits of +.IR flags , +and are defined respectively as 0, 1, and 2. +In other words, the combination +.B "O_RDONLY | O_WRONLY" +is a logical error, and certainly does not have the same meaning as +.BR O_RDWR . -If the file is newly created, its -.IR st_atime , -.IR st_ctime , -.I st_mtime -fields -(respectively, time of last access, time of last status change, and -time of last modification; see -.BR stat (2)) -are set -to the current time, and so are the -.I st_ctime -and -.I st_mtime -fields of the -parent directory. -Otherwise, if the file is modified because of the -.B O_TRUNC -flag, its st_ctime and st_mtime fields are set to the current time. +Linux reserves the special, nonstandard access mode 3 (binary 11) in +.I flags +to mean: +check for read and write permission on the file and return a descriptor +that can't be used for reading or writing. +This nonstandard access mode is used by some Linux drivers to return a +descriptor that is to be used only for device-specific +.BR ioctl (2) +operations. +.\" See for example util-linux's disk-utils/setfdprm.c +.\" For some background on access mode 3, see +.\" http://thread.gmane.org/gmane.linux.kernel/653123 +.\" "[RFC] correct flags to f_mode conversion in __dentry_open" +.\" LKML, 12 Mar 2008 .\" .\" .SS Rationale for openat() and the other *at() calls |