'\" te
.\" Copyright (c) 2007, Sun Microsystems, Inc. All Rights Reserved.
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
.TH FSATTR 7 "Oct 10, 2007"
.SH NAME
fsattr \- extended file attributes
.SH DESCRIPTION
.sp
.LP
Attributes are logically supported as files within the file system.  The file
system is therefore augmented with an orthogonal name space of file attributes.
Any file (including attribute files) can have an arbitrarily deep attribute
tree associated with it. Attribute values are accessed by file descriptors
obtained through a special attribute interface.  This logical view of
"attributes as files" allows the leveraging of existing file system interface
functionality to support the construction, deletion, and manipulation of
attributes.
.sp
.LP
The special files "." and ".\|." retain their accustomed semantics within the
attribute hierarchy.  The "." attribute file refers to the current directory
and the ".\|." attribute file refers to the parent directory.  The unnamed
directory at the head of each attribute tree is considered the "child" of the
file it is associated with and the ".\|." file refers to the associated file.
For any non-directory file with attributes, the ".\|." entry in the unnamed
directory refers to a file that is not a directory.
.sp
.LP
Conceptually, the attribute model is fully general. Extended attributes can be
any type of file (doors, links, directories, and so forth) and can even have
their own attributes (fully recursive).  As a result, the attributes associated
with a file could be an arbitrarily deep directory hierarchy where each
attribute could have an equally complex attribute tree associated with it.  Not
all implementations are able to, or want to, support the full model.
Implementation are therefore permitted to reject operations that are not
supported.  For example, the implementation for the UFS file system allows only
regular files as attributes (for example, no sub-directories) and rejects
attempts to place attributes on attributes.
.sp
.LP
The following list details the operations that are rejected in the current
implementation:
.sp
.ne 2
.na
\fB\fBlink\fR\fR
.ad
.RS 25n
Any attempt to create links between attribute and non-attribute space is
rejected to prevent security-related or otherwise sensitive attributes from
being exposed, and therefore manipulable, as regular files.
.RE

.sp
.ne 2
.na
\fB\fBrename\fR\fR
.ad
.RS 25n
Any attempt to rename between attribute and non-attribute space is rejected to
prevent an already linked file from being renamed and thereby circumventing the
\fBlink\fR restriction above.
.RE

.sp
.ne 2
.na
\fB\fBmkdir\fR, \fBsymlink\fR, \fBmknod\fR\fR
.ad
.RS 25n
Any attempt to create a "non-regular" file in attribute space is rejected to
reduce the functionality, and therefore exposure and risk, of the initial
implementation.
.RE

.sp
.LP
The entire available name space has been allocated to "general use" to bring
the implementation in line with the NFSv4 draft standard [NFSv4]. That standard
defines "named attributes" (equivalent to Solaris Extended Attributes) with no
naming restrictions.  All Sun applications making use of opaque extended
attributes will use the prefix "SUNW".
.SS "Shell-level API"
.sp
.LP
The command interface for extended attributes is the set of applications
provided by Solaris for the manipulation of attributes from the command line.
This interface consists of a set of existing utilities that have been extended
to be "attribute-aware", plus the \fBrunat\fR utility designed to "expose" the
extended attribute space so that extended attributes can be manipulated as
regular files.
.sp
.LP
The \fB-@\fR option enable utilities to manipulate extended attributes. As a
rule, this option enables the utility to enter into attribute space when the
utility is performing a recursive traversal of file system space. This is a
fully recursive concept. If the underlying file system supports recursive
attributes and directory structures, the \fB-@\fR option opens these spaces to
the file tree-walking algorithms.
.sp
.LP
The following utilities accommodate extended attributes (see the individual
manual pages for details):
.sp
.ne 2
.na
\fB\fBcp\fR\fR
.ad
.RS 8n
By default, \fBcp\fR ignores attributes and copies only file data.  This is
intended to maintain the semantics implied by \fBcp\fR currently, where
attributes (such as owner and mode) are not copied unless the \fB-p\fR option
is specified. With the \fB-@\fR (or \fB-p\fR) option, \fBcp\fR attempts to copy
all attributes along with the file data.
.RE

.sp
.ne 2
.na
\fB\fBcpio\fR\fR
.ad
.RS 8n
The \fB-@\fR option informs \fBcpio\fR to archive attributes, but by default
\fBcpio\fR ignores extended attributes. See \fBExtended Archive Formats\fR
below for a description of the new archive records.
.RE

.sp
.ne 2
.na
\fB\fBdu\fR\fR
.ad
.RS 8n
File sizes computed include the space allocated for any extended attributes
present.
.RE

.sp
.ne 2
.na
\fB\fBfind\fR\fR
.ad
.RS 8n
By default, \fBfind\fR ignores attributes.  The \fB-xattr\fR expression
provides support for searches involving attribute space. It returns true if
extended attributes are present on the current file.
.RE

.sp
.ne 2
.na
\fB\fBfsck\fR\fR
.ad
.RS 8n
The \fBfsck\fR utility manages extended attribute data on the disk. A file
system with extended attributes can be mounted on versions of Solaris that are
not attribute-aware (versions prior to Solaris 9), but the attributes will not
be accessible and \fBfsck\fR will strip them from the files and place them in
\fBlost+found\fR. Once the attributes have been stripped the file system is
completely stable on Solaris versions that are not attribute-aware, but would
now be considered corrupted on attribute-aware versions of Solaris. The
attribute-aware \fBfsck\fR utility should be run to stabilize the file system
before using it in an attribute-aware environment.
.RE

.sp
.ne 2
.na
\fB\fBfsdb\fR\fR
.ad
.RS 8n
This \fBfsdb\fR utility is able to find the inode for the "hidden" extended
attribute directory.
.RE

.sp
.ne 2
.na
\fB\fBls\fR\fR
.ad
.RS 8n
The \fBls\fR \fB-@\fR command displays an "@" following the mode information
when extended attributes are present.  More precisely, the output line for a
given file contains an "@" character following the mode characters if the
\fBpathconf\fR(2) variable \fBXATTR_EXISTS\fR is set to true. See the
\fBpathconf()\fR section below.  The \fB-@\fR option uses the same general
output format as the \fB-l\fR option.
.RE

.sp
.ne 2
.na
\fB\fBmv\fR\fR
.ad
.RS 8n
When a file is moved, all attributes are carried along with the file rename.
When a file is moved across a file system boundary, the copy command invoked is
similar to the \fBcp\fR \fB-p\fR variant described above and extended
attributes are "moved". If the extended file attributes cannot be replicated,
the move operation fails and the source file is not removed.
.RE

.sp
.ne 2
.na
\fB\fBpax\fR\fR
.ad
.RS 8n
The \fB-@\fR option informs \fBpax\fR to archive attributes, but by default
\fBpax\fR ignores extended attributes.  The \fBpax\fR(1) utility is a generic
replacement for both \fBtar\fR(1) and \fBcpio\fR(1) and is able to produce
either output format in its archive.  See \fBExtended Archive Formats\fR below
for a description of the new archive records.
.RE

.sp
.ne 2
.na
\fB\fBtar\fR\fR
.ad
.RS 8n
In the default case, \fBtar\fR does not attempt to place attributes in the
archive.  If the \fB-@\fR option is specified, however, \fBtar\fR traverses
into the attribute space of all files being placed in the archive and attempts
to add the attributes to the archive. A new record type has been introduced for
extended attribute entries in \fBtar\fR archive files (the same is true for
\fBpax\fR and \fBcpio\fR archives) similar to the way ACLs records were
defined. See \fBExtended Archive Formats\fR below for a description of the new
archive records.
.RE

.sp
.LP
There is a class of utilities (\fBchmod\fR, \fBchown\fR, \fBchgrp\fR) that one
might expect to be modified in a manner similar to those listed above. For
example, one might expect that performing \fBchmod\fR on a file would not only
affect the file itself but would also affect at least the extended attribute
directory if not any existing extended attribute files.  This is not the case.
The model chosen for extended attributes implies that the attribute directory
and the attributes themselves are all file objects in their own right, and can
therefore have independent file status attributes associated with them  (a
given implementation cannot support this, for example, for intrinsic
attributes).  The relationship is left undefined and a fine-grained control
mechanism (\fBrunat\fR(1)) is provided to allow manipulation of extended
attribute status attributes as necessary.
.sp
.LP
The \fBrunat\fR utility has the following syntax:
.sp
.in +2
.nf
runat \fIfilename\fR [\fIcommand\fR]
.fi
.in -2
.sp

.sp
.LP
The \fBrunat\fR utility executes the supplied command in the context of the
"attribute space" associated with the indicated file.  If no command argument
is supplied, a shell is invoked. See \fBrunat\fR(1) for details.
.SS "Application-level API"
.sp
.LP
The primary interface required to access extended attributes at the
programmatic level is the \fBopenat\fR(2) function. Once a file descriptor has
been obtained for an attribute file by an \fBopenat()\fR call, all normal file
system semantics apply. There is no attempt to place special semantics on
\fBread\fR(2), \fBwrite\fR(2), \fBftruncate\fR(3C), or other functions when
applied to attribute file descriptors relative to "normal" file descriptors.
.sp
.LP
The set of existing attributes can be browsed by calling \fBopenat()\fR with
"." as the file name and the \fBO_XATTR\fR flag set, resulting in a file
descriptor for the attribute directory.  The list of attributes is obtained by
calls to \fBgetdents\fR(2) on the returned file descriptor.  If the target file
did not previously have any attributes associated with it, an empty top-level
attribute directory is created for the file and subsequent \fBgetdents()\fR
calls will return only "." and ".\|.".  While the owner of the parent file owns
the extended attribute directory, it is not charged against its quota if the
directory is empty.  Attribute files themselves, however, are charged against
the user quota as any other regular file.
.sp
.LP
Additional system calls have been provided as convenience functions. These
include the \fBfchownat\fR(2), \fBfstatat\fR(2), \fBfutimesat\fR(2),
\fBrenameat\fR(2), \fBunlinkat\fR(2). These new functions, along with
\fBopenat()\fR, provide a mechanism to access files relative to an arbitrary
point in the file system, rather than only the current working directory.  This
mechanism is particularly useful in situations when a file descriptor is
available with no path. The \fBopenat()\fR function, in particular, can be used
in many contexts where \fBchdir()\fR or \fBfchdir()\fR is currently required.
See \fBchdir\fR(2).
.SS "Open a file relative to a file descriptor"
.sp
.in +2
.nf
int openat (int \fIfd\fR, const char *\fIpath\fR, int \fIoflag\fR [, mode_t \fImode\fR])
.fi
.in -2

.sp
.LP
The \fBopenat\fR(2) function behaves exactly as \fBopen\fR(2) except when given
a relative path.  Where \fBopen()\fR resolves a relative path from the current
working directory, \fBopenat()\fR resolves the path based on the vnode
indicated by the supplied file descriptor. When \fIoflag\fR is \fBO_XATTR\fR,
\fBopenat()\fR interprets the \fIpath\fR argument as an extended attribute
reference. The following code fragment uses \fBopenat()\fR to examine the
attributes of some already opened file:
.sp
.in +2
.nf
dfd = openat(fd, ".", O_RDONLY|O_XATTR);
(void)getdents(dfd, buf, nbytes);
.fi
.in -2

.sp
.LP
If \fBopenat()\fR is passed the special value \fBAT_FDCWD\fR as its first
(\fIfd\fR) argument, its behavior is identical to \fBopen()\fR and the relative
path arguments are interpreted relative to the current working directory. If
the \fBO_XATTR\fR flag is provided to \fBopenat()\fR or to \fBopen()\fR, the
supplied path is interpreted as a reference to an extended attribute on the
current working directory.
.SS "Unlink a file relative to a directory file descriptor"
.sp
.in +2
.nf
int unlinkat (int \fIdirfd\fR, const char *path\fIflag\fR, int flag\fIflag\fR)
.fi
.in -2

.sp
.LP
The \fBunlinkat\fR(2) function deletes an entry from a directory.  The
\fIpath\fR argument indicates the name of the entry to remove. If \fIpath\fR an
absolute path, the \fIdirfd\fR argument is ignored. If it is a relative path,
it is interpreted relative to the directory indicated by the \fIdirfd\fR
argument. If \fIdirfd\fR does not refer to a valid directory, the function
returns \fBENOTDIR\fR.  If the special value \fBAT_FDCWD\fR is specified for
\fIdirfd\fR, a relative path argument is resolved relative to the current
working directory.  If the \fIflag\fR argument is 0, all other semantics of
this function are equivalent to \fBunlink\fR(2).  If \fIflag\fR is set to
\fBAT_REMOVEDIR\fR, all other semantics of this function are equivalent to
\fBrmdir\fR(2).
.SS "Rename a file relative to directories"
.sp
.in +2
.nf
int renameat (int \fIfromfd\fR, const char *\fIold\fR, int \fItofd\fR, const char *\fInew\fR)
.fi
.in -2

.sp
.LP
The \fBrenameat\fR(2) function renames an entry in a directory, possibly moving
the entry into a different directory.  The \fIold\fR argument indicates the
name of the entry to rename.  If this argument is a relative path, it is
interpreted relative to the directory indicated by the \fIfd\fR argument. If it
is an absolute path, the \fIfromfd\fR argument is ignored.  The \fInew\fR
argument indicates the new name for the entry.  If this argument is a relative
path, it is interpreted relative to the directory indicated by the \fItofd\fR
argument. If it is an absolute path, the \fItofd\fR argument is ignored.
.sp
.LP
In the relative path cases, if the directory file descriptor arguments do not
refer to a valid directory, the function returns \fBENOTDIR\fR.  All other
semantics of this function are equivalent to \fBrename\fR(2).
.sp
.LP
If a special value \fBAT_FDCWD\fR is specified for either the \fIfromfd\fR or
\fItofd\fR arguments, their associated path arguments (\fIold\fR and \fInew\fR)
are interpreted relative to the current working directory if they are not
specified as absolute paths. Any attempt to use \fBrenameat()\fR to move a file
that is not an extended attribute into an extended attribute directory (so that
it becomes an extended attribute) will fail. The same is true for an attempt to
move a file that is an extended attribute into a directory that is not an
extended attribute directory.
.SS "Obtain information about a file"
.sp
.in +2
.nf
int fstatat (int \fIfd\fR, const char *\fIpath\fR, struct stat* \fIbuf\fR, int \fIflag\fR)
.fi
.in -2

.sp
.LP
The \fBfstatat\fR(2) function obtains information about a file.  If the
\fIpath\fR argument is relative, it is resolved relative to the \fIfd\fR
argument file descriptor, otherwise the \fIfd\fR argument is ignored.  If the
\fIfd\fR argument is a special value \fBAT_FDCWD\fR the path is resolved
relative to the current working directory.  If the \fIpath\fR argument is a
null pointer, the function returns information about the file referenced by the
\fIfd\fR argument.  In all other relative path cases, if the \fIfd\fR argument
does not refer to a valid directory, the function returns \fBENOTDIR\fR. If
\fBAT_SYMLINK_NOFOLLOW\fR is set in the \fIflag\fR argument, the function will
not automatically traverse a symbolic link at the position of the path. If
\fB_AT_TRIGGER\fR is set in the \fIflag\fR argument and the vnode is a trigger
mount point, the mount is performed and the function returns the attributes of
the root of the mounted filesystem. The \fBfstatat()\fR function is a
multipurpose function that can be used in place of \fBstat()\fR, \fBlstat()\fR,
or \fBfstat()\fR. See \fBstat\fR(2)
.sp
.LP
The function call \fBstat(\fR\fIpath\fR\fB,\fR \fIbuf\fR\fB)\fR is identical to
\fBfstatat(AT_FDCWD\fR, \fIpath\fR\fB,\fR \fIbuf\fR\fB, 0)\fR.
.sp
.LP
The function call \fBlstat(\fR\fIpath\fR\fB,\fR \fIbuf\fR\fB)\fR is identical
to \fBfstatat(AT_FDCWD\fR, \fIpath\fR\fB,\fR \fIbuf\fR,
\fBAT_SYMLINK_NOFOLLOW)\fR
.sp
.LP
The function call \fBfstat(\fR\fIfildes\fR\fB,\fR \fIbuf\fR\fB)\fR is identical
to \fBfstatat(\fR\fIfildes\fR, \fBNULL\fR, \fIbuf\fR, \fB0)\fR.
.SS "Set owner and group ID"
.sp
.in +2
.nf
int fchownat (int \fIfd\fR, const char *\fIpath\fR, uid_t \fIowner\fR, gid_t \fIgroup\fR, \e
          int \fIflag\fR)
.fi
.in -2

.sp
.LP
The \fBfchownat\fR(2) function sets the owner ID and group ID for a file. If
the \fIpath\fR argument is relative, it is resolved relative to the \fIfd\fR
argument file descriptor, otherwise the \fIfd\fR argument is ignored.  If the
\fIfd\fR argument is a special value \fBAT_FDCWD\fR the path is resolved
relative to the current working directory.  If the path argument is a null
pointer, the function sets the owner and group ID of the file referenced by the
\fIfd\fR argument.  In all other relative path cases, if the \fIfd\fR argument
does not refer to a valid directory, the function returns \fBENOTDIR\fR. If the
\fIflag\fR argument is set to \fBAT_SYMLINK_NOFOLLOW\fR, the function will not
automatically traverse a symbolic link at the position of the path. The
\fBfchownat()\fR function is a multi-purpose function that can be used in place
of \fBchown()\fR, \fBlchown()\fR, or \fBfchown()\fR. See \fBchown\fR(2).
.sp
.LP
The function call \fBchown(\fR\fIpath\fR\fB,\fR \fIowner\fR\fB,\fR
\fIgroup\fR\fB)\fR is equivalent to \fBfchownat(AT_FDCWD\fR, \fIpath\fR\fB,\fR
\fIowner\fR\fB,\fR \fIgroup\fR\fB, 0)\fR.
.sp
.LP
The function call \fBlchown(\fR\fIpath\fR\fB,\fR \fIowner\fR\fB,\fR
\fIgroup\fR\fB)\fR is equivalent to \fBfchownat(AT_FDCWD\fR, \fIpath\fR\fB,\fR
\fIowner\fR\fB,\fR \fIgroup\fR\fB, AT_SYMLINK_NOFOLLOW)\fR.
.SS "Set file access and modification times"
.sp
.in +2
.nf
int futimesat (int \fIfd\fR, const char *\fIpath\fR, const struct timeval \e
              \fItimes\fR[2])
.fi
.in -2

.sp
.LP
The \fBfutimesat\fR(2) function sets the access and modification times for a
file.  If the \fIpath\fR argument is relative, it is resolved relative to the
\fIfd\fR argument file descriptor; otherwise the \fIfd\fR argument is ignored.
If the \fIfd\fR argument is the special value \fBAT_FDCWD\fR, the path is
resolved relative to the current working directory.  If the \fIpath\fR argument
is a null pointer, the function sets the access and modification times of the
file referenced by the \fIfd\fR argument. In all other relative path cases, if
the \fIfd\fR argument does not refer to a valid directory, the function returns
\fBENOTDIR\fR.  The \fBfutimesat()\fR function can be used in place of
\fButimes\fR(2).
.sp
.LP
The function call \fButimes(\fR\fIpath\fR\fB,\fR \fItimes\fR\fB)\fR is
equivalent to \fBfutimesat(AT_FDCWD\fR, \fIpath\fR\fB,\fR \fItimes\fR\fB)\fR.
.SS "New pathconf() functionality"
.sp
.in +2
.nf
long int pathconf(const char *\fIpath\fR, int \fIname\fR)
.fi
.in -2

.sp
.LP
Two variables have been added to \fBpathconf\fR(2) to provide enhanced support
for extended attribute manipulation. The \fBXATTR_ENABLED\fR variable allows an
application to determine if attribute support is currently enabled for the file
in question. The \fBXATTR_EXISTS\fR variable allows an application to determine
whether there are any extended attributes associated with the supplied path.
.SS "Open/Create an attribute file"
.sp
.in +2
.nf
int attropen (const char *\fIpath\fR, const char *\fIattrpath\fR, int \fIoflag\fR \e
         [, mode_t \fImode\fR])
.fi
.in -2

.sp
.LP
The \fBattropen\fR(3C) function returns a file descriptor for the named
attribute, \fIattrpath\fR, of the file indicated by \fIpath\fR. The \fIoflag\fR
and \fImode\fR arguments are identical to the \fBopen\fR(2) arguments and are
applied to the open operation on the attribute file (for example, using the
\fBO_CREAT\fR flag creates a new attribute).  Once opened, all normal file
system operations can be used on the attribute file descriptor.  The
\fBattropen()\fR function is a convenience function and is equivalent to the
following sequence of operations:
.sp
.in +2
.nf
fd = open (path, O_RDONLY);
attrfd = openat(fd, attrpath, oflag|O_XATTR, mode);
close(fd);
.fi
.in -2

.sp
.LP
The set of existing attributes can be browsed by calling \fBattropen()\fR with
"." as the attribute name.  The list of attributes is obtained by calling
\fBgetdents\fR(2) (or \fBfdopendir\fR(3C) followed by \fBreaddir\fR(3C), see
below) on the returned file descriptor.
.SS "Convert an open file descriptor for a directory into a directory descriptor"
.sp
.in +2
.nf
DIR * fdopendir (const int \fIfd\fR)
.fi
.in -2

.sp
.LP
The \fBfdopendir\fR(3C) function promotes a file descriptor for a directory to
a directory pointer suitable for use with the \fBreaddir\fR(3C) function. The
originating file descriptor should not be used again following the call to
\fBfdopendir()\fR. The directory pointer should be closed with a call to
\fBclosedir\fR(3C). If the provided file descriptor does not reference a
directory, the function returns \fBENOTDIR\fR. This function is useful in
circumstances where the only available handle on a directory is a file
descriptor. See \fBattropen\fR(3C) and \fBopenat\fR(2).
.SS "Using the API"
.sp
.LP
The following examples demonstrate how the API might be used to perform basic
operations on extended attributes:
.LP
\fBExample 1 \fRList extended attributes on a file.
.sp
.in +2
.nf
attrdirfd = attropen("test", ".", O_RDONLY);
dirp = fdopendir(attrdirfd);
while (dp = readdir(dirp)) {
\&...
.fi
.in -2

.LP
\fBExample 2 \fROpen an extended attribute.
.sp
.in +2
.nf
attrfd = attropen("test", dp->d_name, O_RDONLY);
.fi
.in -2

.sp
.LP
or

.sp
.in +2
.nf
attrfd = openat(attrdirfd, dp->d_name, O_RDONLY);
.fi
.in -2

.LP
\fBExample 3 \fRRead from an extended attribute.
.sp
.in +2
.nf
while (read(attrfd, buf, 512) > 0) {
\&...
.fi
.in -2

.LP
\fBExample 4 \fRCreate an extended attribute.
.sp
.in +2
.nf
newfd = attropen("test", "attr", O_CREAT|O_RDWR);
.fi
.in -2

.sp
.LP
or

.sp
.in +2
.nf
newfd = openat(attrdirfd, "attr", O_CREAT|O_RDWR);
.fi
.in -2

.LP
\fBExample 5 \fRWrite to an extended attribute.
.sp
.in +2
.nf
count = write(newfd, buf, length);
.fi
.in -2

.LP
\fBExample 6 \fRDelete an extended attribute.
.sp
.in +2
.nf
error = unlinkat(attrdirfd, "attr");
.fi
.in -2

.sp
.LP
Applications intending to access the interfaces defined here as well as the
POSIX and X/Open specification-conforming interfaces should define the macro
\fB_ATFILE_SOURCE\fR to be 1 and set whichever feature test macros are
appropriate to obtain the desired environment. See \fBstandards\fR(7).
.SS "Extended Archive Formats"
.sp
.LP
As noted above in the description of command utilities modified to provide
support for extended attributes, the archive formats for \fBtar\fR(1) and
\fBcpio\fR(1) have been extended to provide support for archiving extended
attributes. This section describes the specifics of the archive format
extensions.
.SS "Extended tar format"
.sp
.LP
The \fBtar\fR archive is made up of a series of 512 byte blocks. Each archived
file is represented by a header block and zero or more data blocks containing
the file contents. The header block is structured as shown in the following
table.
.sp

.sp
.TS
c c c
l l l .
Field Name	Length (in Octets)	Description
Name	100	File name string
Mode	8	12 file mode bits
Uid	8	User ID of file owner
Gid	8	Group ID of file owner
Size	12	Size of file
Mtime	12	File modification time
Chksum	8	File contents checksum
Typeflag	1	File type flag
Linkname	100	Link target name if file linked
Magic	6	"ustar"
Version	2	"00"
Uname	32	User name of file owner
Gname	32	Group name of file owner
Devmajor	8	Major device ID if special file
Devminor	8	Minor device ID if special file
Prefix	155	Path prefix string for file
.TE

.sp
.LP
The extended attribute project extends the above header format by defining a
new header type (for the \fBTypeflag\fR field). The type 'E' is defined to be
used for all extended attribute files. Attribute files are stored in the
\fBtar\fR archive as a sequence of two \fB<header ,data>\fR pairs. The first
file contains the data necessary to locate and name the extended attribute in
the file system. The second file contains the actual attribute file data.  Both
files use an 'E' type header. The prefix and name fields in extended attribute
headers are ignored, though they should be set to meaningful values for the
benefit of archivers that do not process these headers. Solaris archivers set
the prefix field to "\fB/dev/null\fR" to prevent archivers that do not
understand the type 'E' header from trying to restore extended attribute files
in inappropriate places.
.SS "Extended cpio format"
.sp
.LP
The \fBcpio\fR archive format is octet-oriented rather than block-oriented.
Each file entry in the archive includes a header that describes the file,
followed by the file name, followed by the contents of the file.  These data
are arranged as described in the following table.
.sp

.sp
.TS
c c c
l l l .
\fBField Name\fR	Length (in Octets)	Description
\fBc_magic\fR	6	70707
\fBc_dev\fR	6	First half of unique file ID
\fBc_ino\fR	6	Second half of unique file ID
\fBc_mode\fR	6	File mode bits
\fBc_uid\fR	6	User ID of file owner
\fBc_gid\fR	6	Group ID of file owner
\fBc_nlink\fR	6	Number of links referencing file
\fBc_rdev\fR	6	Information for special files
\fBc_mtime\fR	11	Modification time of file
\fBc_namesize\fR	6	Length of file pathname
\fBc_filesize\fR	11	Length of file content
\fBc_name\fR	\fBc_namesize\fR	File pathname
\fBc_filedata\fR	\fBc_filesize\fR	File content
.TE

.sp
.LP
The basic archive file structure is not changed for extended attributes. The
file type bits stored in the \fBc_mode\fR field for an attribute file are set
to \fB0xB000\fR. As with the \fBtar\fR archive format, extended attributes are
stored in \fBcpio\fR archives as two consecutive file entries. The first file
describes the location/name for the extended attribute. The second file
contains the actual attribute file content. The \fBc_name\fR field in extended
attribute headers is ignored, though it should be set to a meaningful value for
the benefit of archivers that do not process these headers.  Solaris archivers
start the pathname with "\fB/dev/null/\fR"to prevent archivers that do not
understand the type 'E' header from trying to restore extended attribute files
in inappropriate places.
.SS "Attribute identification data format"
.sp
.LP
Both the \fBtar\fR and \fBcpio\fR archive formats can contain the special files
described above, always paired with the extended attribute data record, for
identifying the precise location of the extended attribute.  These special data
files are necessary because there is no simple naming mechanism for extended
attribute files. Extended attributes are not visible in the file system name
space. The extended attribute name space must be "tunneled into" using the
\fBopenat()\fR function. The attribute identification data must support not
only the flat naming structure for extended attributes, but also the
possibility of future extensions allowing for attribute directory hierarchies
and recursive attributes. The data file is therefore composed of a sequence of
records. It begins with a fixed length header describing  the content. The
following table describes the format of this data file.
.sp

.sp
.TS
c c c
l l l .
Field Name	Length (in Octets)	Description
\fBh_version\fR	7	Name file version
\fBh_size\fR	10	Length of data file
\fBh_component_len\fR	10	Total length of all path segments
\fBh_link_comp_len\fR	10	Total length of all link segments
\fBpath\fR	\fBh_component_len\fR	Complex path
\fBlink_path\fR	\fBh_link_comp_len\fR	Complex link path
.TE

.sp
.LP
As demonstrated above, the header is followed by a record describing the "path"
to the attribute file. This path is composed of two or more path segments
separated by a null character. Each segment describes a path rooted at the
hidden extended attribute directory of the leaf file of the previous segment,
making it possible to name attributes on attributes.  The first segment is
always the path to the parent file that roots the entire sequence in the normal
name space. The following table describes the format of each segment.
.sp

.sp
.TS
c c c
l l l .
Field Name	Length (in Octets)	Description
_
\fBh_namesz\fR	7	Length of segment path
\fBh_typeflag\fR	1	Actual file type of attribute file
\fBh_names\fR	\fBh_namesz\fR	Parent path + segment path
.TE

.sp
.LP
If the attribute file is linked to another file, the path record is followed by
a second record describing the location of the referencing file.  The structure
of this record is identical to the record described above.
.SH SEE ALSO
.sp
.LP
.BR cp (1),
.BR cpio (1),
.BR du (1),
.BR find (1),
.BR ls (1),
.BR mv (1),
.BR pax (1),
.BR runat (1),
.BR tar (1),
.BR chown (2),
.BR link (2),
.BR open (2),
.BR pathconf (2),
.BR rename (2),
.BR stat (2),
.BR unlink (2),
.BR utimes (2),
.BR attropen (3C),
.BR standards (7),
.BR fsck (8)