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stat.2: Update discussion of nanosecond timestamps 

The existing text describes the timestamp fields as 'time_t'
and delegates discussion of nanosecond timestamps under NOTES.
Nanosecond timestamps have been around for a while now,
and are in POSIX.1-2008, so reverse the orientation of the
discussion, putting the nanosecond fields into DESCRIPTION
and detailing the historical situation under NOTES.

Reported-by: Yang Yang <yangyang.gnu@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2013-10-25 15:23:29 +13:00
parent 36e3fa2641
commit e9e9e87ecf
1 changed files with 37 additions and 16 deletions
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53
man2/stat.2
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@ -108,19 +108,28 @@ structure, which contains the following fields:
.in +4n
.nf
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
/* Since Linux 2.6, the kernel supports nanosecond
precision for the following timestamp fields.
For the details before Linux 2.6, see NOTES. */
struct timespec st_atim; /* time of last access */
struct timespec st_mtim; /* time of last modification */
struct timespec st_ctim; /* time of last status change */
#define st_atime st_atim.tv_sec /* Backward compatibility */
#define st_mtime st_mtim.tv_sec
#define st_ctime st_ctim.tv_sec
};
.fi
.in
@ -497,18 +506,30 @@ T}
A sticky command appeared in Version 32V AT&T UNIX.
.SH NOTES
Older kernels and older standards did not support nanosecond timestamp
fields.
Instead, there were three timestamp
.RI fields\(em st_atime ,
.IR st_mtime ,
and
.IR st_ctime \(emtyped
as
.IR time_t
that recorded timestamps with one-second precision.
Since kernel 2.5.48, the
.I stat
structure supports nanosecond resolution for the three file timestamp fields.
Glibc exposes the nanosecond component of each field using names of the form
The nanosecond components of each timestamp are available
via names of the form
.IR st_atim.tv_nsec
if the
.B _BSD_SOURCE
or
.B _SVID_SOURCE
feature test macro is defined.
These fields are specified in POSIX.1-2008, and, starting with version 2.12,
glibc also exposes these field names if
Nanosecond timestamps are nowadays standardized,
starting with POSIX.1-2008, and, starting with version 2.12,
glibc also exposes the nanosecond component names if
.BR _POSIX_C_SOURCE
is defined with the value 200809L or greater, or
.BR _XOPEN_SOURCE