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.\"       $FreeBSD: src/share/man/man9/extattr.9,v 1.1.2.4 2001/12/17 11:30:18 ru Exp $
.\"
.Dd May 8, 2010
.Dt EXTATTR 9
.Os
.Sh NAME
.Nm extattr
.Nd virtual file system named extended attributes
.Sh SYNOPSIS
.In sys/param.h
.In sys/vnode.h
.In sys/extattr.h
.Sh DESCRIPTION
Named extended attributes allow additional meta-data to be associated
with vnodes representing files and directories.
The semantics of this additional data is that of a "name=value" pair, where
a name may be defined or undefined, and if defined, associated with zero or
more bytes of arbitrary binary data.
.Pp
Reads of extended attribute data may return specific contiguous regions of
the meta-data, in the style of
.Xr VOP_READ 9 ,
but writes will replace the entire current "value" associated with
a given name.
As there are a plethora of file systems with differing extended attributes,
availability and functionality of these functions may be limited, and they
should be used with awareness of the underlying semantics of the supporting
file system.
Authorization schemes for extended attribute data may also vary by file
system, as well as maximum attribute size, and whether or not any or
specific new attributes may be defined.
.Pp
Extended attributes are named using a null-terminated character string.
Depending on underlying file system semantics, this name may or may not be
case-sensitive.
Appropriate vnode extended attribute calls are:
.Xr VOP_GETEXTATTR 9
and
.Xr VOP_SETEXTATTR 9 .
.Sh SEE ALSO
.Xr VFS 9 ,
.Xr VOP_GETEXTATTR 9 ,
.Xr VOP_SETEXTATTR 9
.Sh AUTHORS
This manual page was written by
.An Robert Watson .