.\"
.\" Extended attributes system calls manual pages
.\"
.\" (C) Andreas Gruenbacher, February 2001
.\" (C) Silicon Graphics Inc, September 2001
.\"
.TH LISTXATTR 2 "Extended Attributes" "Dec 2001" "System calls"
.SH NAME
listxattr, llistxattr, flistxattr \- list extended attribute names
.SH SYNOPSIS
.fam C
.nf
.B #include <attr/xattr.h>
.sp
.BI "ssize_t listxattr (const char\ *" path ",
.BI "\t\t\t\t char\ *" list ", size_t " size );
.BI "ssize_t llistxattr (const char\ *" path ",
.BI "\t\t\t\t char\ *" list ", size_t " size );
.BI "ssize_t flistxattr (int " filedes ",
.BI "\t\t\t\t char\ *" list ", size_t " size );
.fi
.fam T
.SH DESCRIPTION
Extended attributes are name:value
pairs associated with inodes (files, directories, symlinks, 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 attr (5).
.PP
.B listxattr
retrieves the
.I list
of extended attribute names associated with the given
.I path
in the filesystem.
The list is the set of (NULL-terminated) names, one after the other.
The length of the attribute name
.I list
is returned.
.PP
.B llistxattr
is identical to 
.BR listxattr ,
except in the case of a symbolic link, where the list of names of
extended attributes associated with the link itself is retrieved,
not the file that it refers to.
.PP
.B flistxattr
is identical to
.BR listxattr ,
only the open file pointed to by
.I filedes
(as returned by
.BR open (2))
is interrogated in place of
.IR path .
.PP
A single extended attribute
.I name
is a simple NULL-terminated string.
The name includes a namespace prefix \- there may be several, disjoint
namespaces associated with an individual inode.
.PP
An empty buffer of
.I size
zero can be passed into these calls to return the current size of the
list of extended attribute names, which can be used to estimate the
size of a buffer which is sufficiently large to hold the list of names.
.PP
The interface is designed to allow guessing of initial buffer
sizes, and to enlarge buffers when the return value indicates
that the buffer provided was too small.
.SH EXAMPLES
The
.I list
of names is returned as an unordered array of NULL-terminated character
strings (attribute names are separated by NULL characters), like this:
.fam C
.RS
.nf
user.name1\\0system.name1\\0user.name2\\0
.fi
.RE
.fam T
.P
Filesystems like ext2, ext3 and XFS which implement POSIX ACLs using
extended attributes, might return a
.I list
like this:
.fam C
.RS
.nf
system.posix_acl_access\\0system.posix_acl_default\\0
.fi
.RE
.fam T
.SH RETURN VALUE
On success, a positive number is returned indicating the size of the
extended attribute name list.
On failure, \-1 is returned and
.I errno
is set appropriately.
.PP
If the
.I size
of the
.I list
buffer is too small to hold the result,
.I errno
is set to ERANGE.
.PP
If extended attributes are not supported by the filesystem, or are disabled,
.I errno
is set to ENOTSUP.
.PP
The errors documented for the
.BR stat (2)
system call are also applicable here.
.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 SEE ALSO
.BR getfattr (1),
.BR setfattr (1),
.BR open (2),
.BR stat (2),
.BR getxattr (2),
.BR setxattr (2),
.BR removexattr (2),
and
.BR attr (5).