man-pages/man2/getxattr.2

.\" Copyright (C) Andreas Gruenbacher, February 2001
.\" Copyright (C) Silicon Graphics Inc, September 2001
.\"
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.TH GETXATTR 2 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
getxattr, lgetxattr, fgetxattr \- retrieve an extended attribute value
.SH SYNOPSIS
.fam C
.nf
.B #include <sys/xattr.h>
.PP
.BI "ssize_t getxattr(const char *" path ", const char *" name ,
.BI "                 void *" value ", size_t " size );
.BI "ssize_t lgetxattr(const char *" path ", const char *" name ,
.BI "                 void *" value ", size_t " size );
.BI "ssize_t fgetxattr(int " fd ", const char *" name ,
.BI "                 void *" value ", size_t " size );
.fi
.fam T
.SH DESCRIPTION
Extended attributes are
.IR name :\c
.I value
pairs associated with inodes (files, directories, symbolic links, etc.).
They are extensions to the normal attributes which are associated
with all inodes in the system (i.e., the
.BR stat (2)
data).
A complete overview of extended attributes concepts can be found in
.BR xattr (7).
.PP
.BR getxattr ()
retrieves the value of the extended attribute identified by
.I name
and associated with the given
.I path
in the filesystem.
The attribute value is placed in the buffer pointed to by
.IR value ;
.I size
specifies the size of that buffer.
The return value of the call is the number of bytes placed in
.IR value .
.PP
.BR lgetxattr ()
is identical to
.BR getxattr (),
except in the case of a symbolic link, where the link itself is
interrogated, not the file that it refers to.
.PP
.BR fgetxattr ()
is identical to
.BR getxattr (),
only the open file referred to by
.I fd
(as returned by
.BR open (2))
is interrogated in place of
.IR path .
.PP
An extended attribute
.I name
is a null-terminated string.
The name includes a namespace prefix; there may be several, disjoint
namespaces associated with an individual inode.
The value of an extended attribute is a chunk of arbitrary textual or
binary data that was assigned using
.BR setxattr (2).
.PP
If
.I size
is specified as zero, these calls return the current size of the
named extended attribute (and leave
.I value
unchanged).
This can be used to determine the size of the buffer that
should be supplied in a subsequent call.
(But, bear in mind that there is a possibility that the
attribute value may change between the two calls,
so that it is still necessary to check the return status
from the second call.)
.SH RETURN VALUE
On success, these calls return a nonnegative value which is
the size (in bytes) of the extended attribute value.
On failure, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B E2BIG
The size of the attribute value is larger than the maximum size allowed; the
attribute cannot be retrieved.
This can happen on filesystems that support
very large attribute values such as NFSv4, for example.
.TP
.B ENODATA
The named attribute does not exist, or the process has no access to
this attribute.
.\" .RB ( ENOATTR
.\" is defined to be a synonym for
.\" .BR ENODATA
.\" in
.\" .IR <attr/attributes.h> .)
.TP
.B ENOTSUP
Extended attributes are not supported by the filesystem, or are disabled.
.TP
.B ERANGE
The
.I size
of the
.I value
buffer is too small to hold the result.
.PP
In addition, the errors documented in
.BR stat (2)
can also occur.
.SH VERSIONS
These system calls have been available on Linux since kernel 2.4;
glibc support is provided since version 2.3.
.SH CONFORMING TO
These system calls are Linux-specific.
.\" .SH AUTHORS
.\" Andreas Gruenbacher,
.\" .RI < a.gruenbacher@computer.org >
.\" and the SGI XFS development team,
.\" .RI < linux-xfs@oss.sgi.com >.
.\" Please send any bug reports or comments to these addresses.
.SH EXAMPLES
See
.BR listxattr (2).
.SH SEE ALSO
.BR getfattr (1),
.BR setfattr (1),
.BR listxattr (2),
.BR open (2),
.BR removexattr (2),
.BR setxattr (2),
.BR stat (2),
.BR symlink (7),
.BR xattr (7)