From f14d3a310dbaf5456e5267ee56d2b35a78ec540b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nikola=20Forr=C3=B3?= <nforro@redhat.com>
Date: Mon, 22 May 2017 14:54:07 +0200
Subject: [PATCH 2/2] stat.2: update to cover latest things used in RHEL 7
---
man-pages/man2/stat.2 | 760 +++++++++++++++++++++++++++++++++++---------------
1 file changed, 540 insertions(+), 220 deletions(-)
diff --git a/man-pages/man2/stat.2 b/man-pages/man2/stat.2
index c86ebc0..f108020 100644
--- a/man-pages/man2/stat.2
+++ b/man-pages/man2/stat.2
@@ -1,7 +1,7 @@
'\" t
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\" Parts Copyright (c) 1995 Nicolai Langfeldt (janl@ifi.uio.no), 1/1/95
-.\" and Copyright (c) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
+.\" and Copyright (c) 2006, 2007, 2014 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
@@ -37,21 +37,30 @@
.\" 2007-06-08 mtk: Added example program
.\" 2007-07-05 mtk: Added details on underlying system call interfaces
.\"
-.TH STAT 2 2012-11-11 "Linux" "Linux Programmer's Manual"
+.TH STAT 2 2017-03-13 "Linux" "Linux Programmer's Manual"
.SH NAME
-stat, fstat, lstat \- get file status
+stat, fstat, lstat, fstatat \- get file status
.SH SYNOPSIS
+.nf
.B #include <sys/types.h>
.br
.B #include <sys/stat.h>
.br
.B #include <unistd.h>
.sp
-.BI "int stat(const char *" path ", struct stat *" buf );
+.BI "int stat(const char *" pathname ", struct stat *" buf );
.br
.BI "int fstat(int " fd ", struct stat *" buf );
.br
-.BI "int lstat(const char *" path ", struct stat *" buf );
+.BI "int lstat(const char *" pathname ", struct stat *" buf );
+.sp
+.BR "#include <fcntl.h> " "/* Definition of AT_* constants */"
+.B #include <sys/stat.h>
+.sp
+.BI "int fstatat(int " dirfd ", const char *" pathname ", struct stat *" \
+buf ,
+.BI " int " flags );
+.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
@@ -62,45 +71,67 @@ Feature Test Macro Requirements for glibc (see
.sp
.BR lstat ():
.RS 4
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
-_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+/* glibc 2.19 and earlier */ _BSD_SOURCE
+.br
+ || /* Since glibc 2.20 */ _DEFAULT_SOURCE
.br
-|| /* Since glibc 2.10: */ _POSIX_C_SOURCE\ >=\ 200112L
+ || _XOPEN_SOURCE\ >=\ 500
+.\" _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+.br
+ || /* Since glibc 2.10: */ _POSIX_C_SOURCE\ >=\ 200112L
+.RE
+.sp
+.BR fstatat ():
+.PD 0
+.ad l
+.RS 4
+.TP 4
+Since glibc 2.10:
+_POSIX_C_SOURCE\ >=\ 200809L
+.TP
+Before glibc 2.10:
+_ATFILE_SOURCE
.RE
.PD
.ad
.SH DESCRIPTION
.PP
-These functions return information about a file.
+These functions return information about a file, in the buffer pointed to by
+.IR buf .
No permissions are required on the file itself, but\(emin the case of
-.BR stat ()
+.BR stat (),
+.BR fstatat (),
and
-.BR lstat ()
-\(em
-execute (search) permission is required on all of the directories in
-.I path
+.BR lstat ()\(emexecute
+(search) permission is required on all of the directories in
+.I pathname
that lead to the file.
.PP
.BR stat ()
-stats the file pointed to by
-.I path
-and fills in
-.IR buf .
+and
+.BR fstatat ()
+retrieve information about the file pointed to by
+.IR pathname ;
+the differences for
+.BR fstatat ()
+are described below.
.BR lstat ()
is identical to
.BR stat (),
except that if
-.I path
-is a symbolic link, then the link itself is stat-ed,
+.I pathname
+is a symbolic link, then it returns information about the link itself,
not the file that it refers to.
.BR fstat ()
is identical to
.BR stat (),
-except that the file to be stat-ed is specified by the file descriptor
+except that the file about which information is to be retrieved
+is specified by the file descriptor
.IR fd .
-.PP
+.\"
+.SS The stat structure
All of these system calls return a
.I stat
structure, which contains the following fields:
@@ -108,84 +139,123 @@ 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 file system 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; /* file type and mode */
+ 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
-.PP
-The
+
+.IR Note :
+the order of fields in the
+.I stat
+structure varies somewhat
+across architectures.
+In addition,
+the definition above does not show the padding bytes
+that may be present between some fields on various architectures.
+Consult the glibc and kernel source code
+if you need to know the details.
+
+.\" Background: inode attributes are modified with i_mutex held, but
+.\" read by stat() without taking the mutex.
+.IR Note :
+For performance and simplicity reasons, different fields in the
+.I stat
+structure may contain state information from different moments
+during the execution of the system call.
+For example, if
+.IR st_mode
+or
+.IR st_uid
+is changed by another process by calling
+.BR chmod (2)
+or
+.BR chown (2),
+.BR stat ()
+might return the old
+.I st_mode
+together with the new
+.IR st_uid ,
+or the old
+.I st_uid
+together with the new
+.IR st_mode .
+
+The fields in the
+.I stat
+structure are as follows:
+.TP
.I st_dev
-field describes the device on which this file resides.
+This field describes the device on which this file resides.
(The
.BR major (3)
and
.BR minor (3)
macros may be useful to decompose the device ID in this field.)
-
-The
+.TP
+.I st_ino
+This field contains the file's inode number.
+.TP
+.I st_mode
+See the discussion of file type and mode, below.
+.TP
+.I st_nlink
+This field contains the number of hard links to the file.
+.TP
+.I st_uid
+This field contains the user ID of the owner of the file.
+.TP
+.I st_gid
+This field contains the ID of the group owner of the file.
+.TP
.I st_rdev
-field describes the device that this file (inode) represents.
-
-The
+This field describes the device that this file (inode) represents.
+.TP
.I st_size
-field gives the size of the file (if it is a regular
+This field gives the size of the file (if it is a regular
file or a symbolic link) in bytes.
The size of a symbolic link is the length of the pathname
it contains, without a terminating null byte.
-
-The
+.TP
+.I st_blksize
+This field gives the "preferred" blocksize for efficient filesystem I/O.
+(Writing to a file in smaller chunks may cause
+an inefficient read-modify-rewrite.)
+.TP
.I st_blocks
-field indicates the number of blocks allocated to the file, 512-byte units.
+This field indicates the number of blocks allocated to the file,
+512-byte units.
(This may be smaller than
.IR st_size /512
when the file has holes.)
-
-The
-.I st_blksize
-field gives the "preferred" blocksize for efficient file system I/O.
-(Writing to a file in smaller chunks may cause
-an inefficient read-modify-rewrite.)
-.PP
-Not all of the Linux file systems implement all of the time fields.
-Some file system types allow mounting in such a way that file
-and/or directory accesses do not cause an update of the
-.I st_atime
-field.
-(See
-.IR noatime ,
-.IR nodiratime ,
-and
-.I relatime
-in
-.BR mount (8),
-and related information in
-.BR mount (2).)
-In addition,
-.I st_atime
-is not updated if a file is opened with the
-.BR O_NOATIME ;
-see
-.BR open (2).
-
-The field
+.TP
.I st_atime
-is changed by file accesses, for example, by
+This is the file's last access timestamp.
+It is changed by file accesses, for example, by
.BR execve (2),
.BR mknod (2),
.BR pipe (2),
-.BR utime (2)
+.BR utime (2),
and
.BR read (2)
(of more than zero bytes).
@@ -193,13 +263,13 @@ Other routines, like
.BR mmap (2),
may or may not update
.IR st_atime .
-
-The field
+.TP
.I st_mtime
-is changed by file modifications, for example, by
+This is the file's last modification timestamp.
+It is changed by file modifications, for example, by
.BR mknod (2),
.BR truncate (2),
-.BR utime (2)
+.BR utime (2),
and
.BR write (2)
(of more than zero bytes).
@@ -212,15 +282,78 @@ The
field is
.I not
changed for changes in owner, group, hard link count, or mode.
-
-The field
+.TP
.I st_ctime
-is changed by writing or by setting inode information
+This is the file's last status change timestamp.
+It is changed by writing or by setting inode information
(i.e., owner, group, link count, mode, etc.).
.PP
-The following POSIX macros are defined to check the file type using the
+Not all of the Linux filesystems implement all of the time fields.
+Some filesystem types allow mounting in such a way that file
+and/or directory accesses do not cause an update of the
+.I st_atime
+field.
+(See
+.IR noatime ,
+.IR nodiratime ,
+and
+.I relatime
+in
+.BR mount (8),
+and related information in
+.BR mount (2).)
+In addition,
+.I st_atime
+is not updated if a file is opened with the
+.BR O_NOATIME
+flag; see
+.BR open (2).
+.\"
+.SS The file type and mode (st_mode)
+POSIX refers to the
+.I st_mode
+bits corresponding to the mask
+.B S_IFMT
+(see below) as the
+.IR "file type" ,
+the 12 bits corresponding to the mask 07777 as the
+.IR "file mode bits"
+and the least significant 9 bits (0777) as the
+.IR "file permission bits" .
+.PP
+The following mask values are defined for the file type of the
.I st_mode
field:
+.in +4n
+.TS
+lB l l.
+S_IFMT 0170000 bit mask for the file type bit field
+
+S_IFSOCK 0140000 socket
+S_IFLNK 0120000 symbolic link
+S_IFREG 0100000 regular file
+S_IFBLK 0060000 block device
+S_IFDIR 0040000 directory
+S_IFCHR 0020000 character device
+S_IFIFO 0010000 FIFO
+.TE
+.in
+.PP
+Thus, to test for a regular file (for example), one could write:
+
+.nf
+.in +4n
+stat(pathname, &sb);
+if ((sb.st_mode & S_IFMT) == S_IFREG) {
+ /* Handle regular file */
+}
+.in
+.fi
+.PP
+Because tests of the above form are common, additional
+macros are defined by POSIX to allow the test of the file type in
+.I st_mode
+to be written more concisely:
.RS 4
.TP 1.2i
.BR S_ISREG (m)
@@ -245,42 +378,85 @@ symbolic link? (Not in POSIX.1-1996.)
socket? (Not in POSIX.1-1996.)
.RE
.PP
-The following flags are defined for the
+The preceding code snippet could thus be rewritten as:
+
+.nf
+.in +4n
+stat(pathname, &sb);
+if (S_ISREG(sb.st_mode)) {
+ /* Handle regular file */
+}
+.in
+.fi
+.PP
+The definitions of most of the above file type test macros
+are provided if any of the following feature test macros is defined:
+.BR _BSD_SOURCE
+(in glibc 2.19 and earlier),
+.BR _SVID_SOURCE
+(in glibc 2.19 and earlier),
+or
+.BR _DEFAULT_SOURCE
+(in glibc 2.20 and later).
+In addition, definitions of all of the above macros except
+.BR S_IFSOCK
+and
+.BR S_ISSOCK ()
+are provided if
+.BR _XOPEN_SOURCE
+is defined.
+The definition of
+.BR S_IFSOCK
+can also be exposed by defining
+.BR _XOPEN_SOURCE
+with a value of 500 or greater.
+
+The definition of
+.BR S_ISSOCK ()
+is exposed if any of the following feature test macros is defined:
+.BR _BSD_SOURCE
+(in glibc 2.19 and earlier),
+.BR _DEFAULT_SOURCE
+(in glibc 2.20 and later),
+.BR _XOPEN_SOURCE
+with a value of 500 or greater, or
+.BR _POSIX_C_SOURCE
+with a value of 200112L or greater.
+.PP
+The following mask values are defined for
+the file mode component of the
.I st_mode
field:
.in +4n
.TS
lB l l.
-S_IFMT 0170000 bit mask for the file type bit fields
-S_IFSOCK 0140000 socket
-S_IFLNK 0120000 symbolic link
-S_IFREG 0100000 regular file
-S_IFBLK 0060000 block device
-S_IFDIR 0040000 directory
-S_IFCHR 0020000 character device
-S_IFIFO 0010000 FIFO
-S_ISUID 0004000 set-user-ID bit
-S_ISGID 0002000 set-group-ID bit (see below)
-S_ISVTX 0001000 sticky bit (see below)
-S_IRWXU 00700 mask for file owner permissions
-S_IRUSR 00400 owner has read permission
-S_IWUSR 00200 owner has write permission
-S_IXUSR 00100 owner has execute permission
-S_IRWXG 00070 mask for group permissions
-S_IRGRP 00040 group has read permission
-S_IWGRP 00020 group has write permission
-S_IXGRP 00010 group has execute permission
-S_IRWXO 00007 mask for permissions for others (not in group)
-S_IROTH 00004 others have read permission
-S_IWOTH 00002 others have write permission
-S_IXOTH 00001 others have execute permission
+S_ISUID 04000 set-user-ID bit
+S_ISGID 02000 set-group-ID bit (see below)
+S_ISVTX 01000 sticky bit (see below)
+
+S_IRWXU 00700 owner has read, write, and execute permission
+S_IRUSR 00400 owner has read permission
+S_IWUSR 00200 owner has write permission
+S_IXUSR 00100 owner has execute permission
+
+S_IRWXG 00070 group has read, write, and execute permission
+S_IRGRP 00040 group has read permission
+S_IWGRP 00020 group has write permission
+S_IXGRP 00010 group has execute permission
+
+S_IRWXO 00007 T{
+others (not in group) have read, write, and execute permission
+T}
+S_IROTH 00004 others have read permission
+S_IWOTH 00002 others have write permission
+S_IXOTH 00001 others have execute permission
.TE
.in
.P
The set-group-ID bit
.RB ( S_ISGID )
has several special uses.
-For a directory it indicates that BSD semantics is to be used
+For a directory, it indicates that BSD semantics is to be used
for that directory: files created there inherit their group ID from
the directory, not from the effective group ID of the creating process,
and directories created there will also get the
@@ -297,6 +473,100 @@ on a directory means that a file
in that directory can be renamed or deleted only by the owner
of the file, by the owner of the directory, and by a privileged
process.
+.\"
+.\"
+.SS fstatat()
+The
+.BR fstatat ()
+system call operates in exactly the same way as
+.BR stat (),
+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
+.I dirfd
+(rather than relative to the current working directory of
+the calling process, as is done by
+.BR stat ()
+for a relative pathname).
+
+If
+.I pathname
+is relative and
+.I dirfd
+is the special value
+.BR AT_FDCWD ,
+then
+.I pathname
+is interpreted relative to the current working
+directory of the calling process (like
+.BR stat ()).
+
+If
+.I pathname
+is absolute, then
+.I dirfd
+is ignored.
+
+.I flags
+can either be 0, or include one or more of the following flags ORed:
+.TP
+.BR AT_EMPTY_PATH " (since Linux 2.6.39)"
+.\" commit 65cfc6722361570bfe255698d9cd4dccaf47570d
+If
+.I pathname
+is an empty string, operate on the file referred to by
+.IR dirfd
+(which may have been obtained using the
+.BR open (2)
+.B O_PATH
+flag).
+In this case,
+.I dirfd
+can refer to any type of file, not just a directory.
+If
+.I dirfd
+is
+.BR AT_FDCWD ,
+the call operates on the current working directory.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.BR AT_NO_AUTOMOUNT " (since Linux 2.6.38)"
+Don't automount the terminal ("basename") component of
+.I pathname
+if it is a directory that is an automount point.
+This allows the caller to gather attributes of an automount point
+(rather than the location it would mount).
+This flag can be used in tools that scan directories
+to prevent mass-automounting of a directory of automount points.
+The
+.B AT_NO_AUTOMOUNT
+flag has no effect if the mount point has already been mounted over.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
+.TP
+.B AT_SYMLINK_NOFOLLOW
+If
+.I pathname
+is a symbolic link, do not dereference it:
+instead return information about the link itself, like
+.BR lstat ().
+(By default,
+.BR fstatat ()
+dereferences symbolic links, like
+.BR stat ().)
+.PP
+See
+.BR openat (2)
+for an explanation of the need for
+.BR fstatat ().
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
@@ -307,13 +577,13 @@ is set appropriately.
.B EACCES
Search permission is denied for one of the directories
in the path prefix of
-.IR path .
+.IR pathname .
(See also
.BR path_resolution (7).)
.TP
.B EBADF
.I fd
-is bad.
+is not a valid open file descriptor.
.TP
.B EFAULT
Bad address.
@@ -322,26 +592,26 @@ Bad address.
Too many symbolic links encountered while traversing the path.
.TP
.B ENAMETOOLONG
-.I path
+.I pathname
is too long.
.TP
.B ENOENT
A component of
-.I path
+.I pathname
does not exist, or
-.I path
-is an empty string.
+.I pathname
+is an empty string and AT_EMPTY_PATH was not specified.
.TP
.B ENOMEM
Out of memory (i.e., kernel memory).
.TP
.B ENOTDIR
A component of the path prefix of
-.I path
+.I pathname
is not a directory.
.TP
.B EOVERFLOW
-.I path
+.I pathname
or
.I fd
refers to a file whose size, inode number,
@@ -358,8 +628,32 @@ calls
on a file whose size exceeds
.I (1<<31)-1
bytes.
+.PP
+The following additional errors can occur for
+.BR fstatat ():
+.TP
+.B EBADF
+.I dirfd
+is not a valid file descriptor.
+.TP
+.B EINVAL
+Invalid flag specified in
+.IR flags .
+.TP
+.B ENOTDIR
+.I pathname
+is relative and
+.I dirfd
+is a file descriptor referring to a file other than a directory.
+.SH VERSIONS
+.BR fstatat ()
+was added to Linux in kernel 2.6.16;
+library support was added to glibc in version 2.4.
.SH CONFORMING TO
-These system calls conform to SVr4, 4.3BSD, POSIX.1-2001.
+.BR stat (),
+.BR fstat (),
+.BR lstat ():
+SVr4, 4.3BSD, POSIX.1-2001, POSIX.1.2008.
.\" SVr4 documents additional
.\" .BR fstat ()
.\" error conditions EINTR, ENOLINK, and EOVERFLOW. SVr4
@@ -369,18 +663,21 @@ These system calls conform to SVr4, 4.3BSD, POSIX.1-2001.
.\" .BR lstat ()
.\" error conditions EINTR, EMULTIHOP, ENOLINK, and EOVERFLOW.
+.BR fstatat ():
+POSIX.1-2008.
+
According to POSIX.1-2001,
.BR lstat ()
on a symbolic link need return valid information only in the
.I st_size
-field and the file-type component of the
+field and the file type of the
.IR st_mode
field of the
.IR stat
structure.
-POSIX.-2008 tightens the specification, requiring
+POSIX.1-2008 tightens the specification, requiring
.BR lstat ()
-to return valid information in all fields except the permission bits in
+to return valid information in all fields except the mode bits in
.IR st_mode .
Use of the
@@ -413,10 +710,10 @@ POSIX.1-1990 did not describe the
.BR S_IFCHR ,
.BR S_IFIFO ,
.B S_ISVTX
-constants, but instead demanded the use of
+constants, but instead specified the use of
the macros
.BR S_ISDIR (),
-etc.
+and so on.
The
.BR S_IF*
constants are present in POSIX.1-2001 and later.
@@ -425,11 +722,11 @@ The
.BR S_ISLNK ()
and
.BR S_ISSOCK ()
-macros are not in
+macros were not in
POSIX.1-1996, but both are present in POSIX.1-2001;
the former is from SVID 4, the latter from SUSv2.
.LP
-UNIX V7 (and later systems) had
+UNIX\ V7 (and later systems) had
.BR S_IREAD ,
.BR S_IWRITE ,
.BR S_IEXEC ,
@@ -438,104 +735,74 @@ prescribes the synonyms
.BR S_IRUSR ,
.BR S_IWUSR ,
.BR S_IXUSR .
-.SS Other systems
-Values that have been (or are) in use on various systems:
-.ad l
-.TS
-l l l l l.
-hex name ls octal description
-f000 S_IFMT 170000 mask for file type
-0000 000000 T{
-SCO out-of-service inode; BSD unknown type; SVID-v2 and XPG2
-have both 0 and 0100000 for ordinary file
-T}
-1000 S_IFIFO p| 010000 FIFO (named pipe)
-2000 S_IFCHR c 020000 character special (V7)
-3000 S_IFMPC 030000 multiplexed character special (V7)
-4000 S_IFDIR d/ 040000 directory (V7)
-5000 S_IFNAM 050000 T{
-XENIX named special file with two subtypes, distinguished by
-\fIst_rdev\fP values 1, 2
-T}
-0001 S_INSEM s 000001 XENIX semaphore subtype of IFNAM
-0002 S_INSHD m 000002 XENIX shared data subtype of IFNAM
-6000 S_IFBLK b 060000 block special (V7)
-7000 S_IFMPB 070000 multiplexed block special (V7)
-8000 S_IFREG - 100000 regular (V7)
-9000 S_IFCMP 110000 VxFS compressed
-9000 S_IFNWK n 110000 network special (HP-UX)
-a000 S_IFLNK l@ 120000 symbolic link (BSD)
-b000 S_IFSHAD 130000 T{
-Solaris shadow inode for ACL (not seen by user space)
-T}
-c000 S_IFSOCK s= 140000 socket (BSD; also "S_IFSOC" on VxFS)
-d000 S_IFDOOR D> 150000 Solaris door
-e000 S_IFWHT w% 160000 BSD whiteout (not used for inode)
-0200 S_ISVTX 001000 T{
-sticky bit: save swapped text even after use (V7)
-.br
-reserved (SVID-v2)
-.br
-On nondirectories: don't cache this file (SunOS)
-.br
-On directories: restricted deletion flag (SVID-v4.2)
-T}
-0400 S_ISGID 002000 T{
-set-group-ID on execution (V7)
-.br
-for directories: use BSD semantics for propagation of GID
-T}
-0400 S_ENFMT 002000 T{
-System V file locking enforcement (shared with S_ISGID)
-T}
-0800 S_ISUID 004000 set-user-ID on execution (V7)
-0800 S_CDF 004000 T{
-directory is a context dependent file (HP-UX)
-T}
-.TE
-.ad
-
-A sticky command appeared in Version 32V AT&T UNIX.
.SH NOTES
+On Linux,
+.BR lstat ()
+will generally not trigger automounter action, whereas
+.BR stat ()
+will (but see the description of
+.BR fstatat ()
+.B AT_NO_AUTOMOUNT
+fag, above).
+
+For pseudofiles that are autogenerated by the kernel,
+.BR stat ()
+does not return an accurate value in the
+.IR st_size
+field.
+For example, the value 0 is returned for many files under the
+.I /proc
+directory,
+while various files under
+.IR /sys
+report a size of 4096 bytes, even though the file content is smaller.
+For such files, one should simply try to read as many bytes as possible
+(and append \(aq\e0\(aq to the returned buffer
+if it is to be interpreted as a string).
+.\"
+.SS Timestamp fields
+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
-.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
+The nanosecond components of each timestamp are available
+via names of the form
+.IR st_atim.tv_nsec ,
+if suitable feature test macros are defined.
+Nanosecond timestamps were standardized in POSIX.1-2008,
+and, starting with version 2.12,
+glibc exposes the nanosecond component names if
.BR _POSIX_C_SOURCE
is defined with the value 200809L or greater, or
.BR _XOPEN_SOURCE
is defined with the value 700 or greater.
+Up to and including glibc 2.19,
+the definitions of the nanoseconds components are also defined if
+.B _BSD_SOURCE
+or
+.B _SVID_SOURCE
+is defined.
If none of the aforementioned macros are defined,
then the nanosecond values are exposed with names of the form
.IR st_atimensec .
-On file systems that do not support subsecond timestamps,
-the nanosecond fields are returned with the value 0.
-.\" As at kernel 2.6.25, XFS and JFS support nanosecond timestamps,
-.\" but ext2, ext3, and Reiserfs do not.
-
-On Linux,
-.BR lstat ()
-will generally not trigger automounter action, whereas
-.BR stat ()
-will (but see
-.BR fstatat (2)).
-For most files under the
-.I /proc
-directory,
-.BR stat ()
-does not return the file size in the
-.I st_size
-field; instead the field is returned with the value 0.
-.SS Underlying kernel interface
+Nanosecond timestamps are supported on XFS, JFS, Btrfs, and
+ext4 (since Linux 2.6.23).
+.\" commit ef7f38359ea8b3e9c7f2cae9a4d4935f55ca9e80
+Nanosecond timestamps are not supported in ext2, ext3, and Reiserfs.
+On filesystems that do not support subsecond timestamps,
+the nanosecond fields are returned with the value 0.
+.SS C library/kernel differences
Over time, increases in the size of the
.I stat
structure have led to three successive versions of
@@ -548,17 +815,51 @@ structure have led to three successive versions of
.IR __NR_stat ),
and
.I sys_stat64()
-(new in kernel 2.4; slot
-.IR __NR_stat64 ).
+(slot
+.IR __NR_stat64 )
+on 32-bit platforms such as i386.
+The first two versions were already present in Linux 1.0
+(albeit with different names);
+.\" See include/asm-i386/stat.h in the Linux 2.4 source code for the
+.\" various versions of the structure definitions
+the last was added in Linux 2.4.
+Similar remarks apply for
+.BR fstat ()
+and
+.BR lstat ().
+
+The kernel-internal versions of the
+.I stat
+structure dealt with by the different versions are, respectively:
+.TP
+.IR __old_kernel_stat
+The original structure, with rather narrow fields, and no padding.
+.TP
+.IR stat
+Larger
+.I st_ino
+field and padding added to various parts of the structure to
+allow for future expansion.
+.TP
+.IR stat64
+Even larger
+.I st_ino
+field,
+larger
+.I st_uid
+and
+.I st_gid
+fields to accommodate the Linux-2.4 expansion of UIDs and GIDs to 32 bits,
+and various other enlarged fields and further padding in the structure.
+(Various padding bytes were eventually consumed in Linux 2.6,
+with the advent of 32-bit device IDs and nanosecond components
+for the timestamp fields.)
+.PP
The glibc
.BR stat ()
wrapper function hides these details from applications,
invoking the most recent version of the system call provided by the kernel,
and repacking the returned information if required for old binaries.
-Similar remarks apply for
-.BR fstat ()
-and
-.BR lstat ().
.\"
.\" A note from Andries Brouwer, July 2007
.\"
@@ -587,6 +888,20 @@ and
.\" interface, rather than the libc-kernel interface.
.\"
.\" (Note that the details depend on gcc being used as c compiler.)
+
+On modern 64-bit systems, life is simpler: there is a single
+.BR stat ()
+system call and the kernel deals with a
+.I stat
+structure that contains fields of a sufficient size.
+
+The underlying system call employed by the glibc
+.BR fstatat ()
+wrapper function is actually called
+.BR fstatat64 ()
+or, on some architectures,
+.\" strace(1) shows the name "newfstatat" on x86-64
+.BR newfstatat ().
.SH EXAMPLE
The following program calls
.BR stat ()
@@ -600,6 +915,7 @@ structure.
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
+#include <sys/sysmacros.h>
int
main(int argc, char *argv[])
@@ -616,6 +932,9 @@ main(int argc, char *argv[])
exit(EXIT_FAILURE);
}
+ printf("ID of containing device: [%lx,%lx]\\n",
+ (long) major(sb.st_dev), (long) minor(sb.st_dev));
+
printf("File type: ");
switch (sb.st_mode & S_IFMT) {
@@ -653,10 +972,11 @@ main(int argc, char *argv[])
}
.fi
.SH SEE ALSO
+.BR ls (1),
+.BR stat (1),
.BR access (2),
.BR chmod (2),
.BR chown (2),
-.BR fstatat (2),
.BR readlink (2),
.BR utime (2),
.BR capabilities (7),
--
2.7.4