1.\" $NetBSD: extattr.9,v 1.4 2009/03/09 19:24:32 joerg Exp $ 2.\" 3.\" Copyright (c) 1999, 2000, 2001, 2003 Robert N. M. Watson 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" FreeBSD: src/share/man/man9/extattr.9,v 1.14 2003/10/23 02:33:03 hmp Exp 28.\" 29.Dd January 2, 2005 30.Dt EXTATTR 9 31.Os 32.Sh NAME 33.Nm extattr 34.Nd file system extended attributes 35.Sh SYNOPSIS 36.In sys/param.h 37.In sys/vnode.h 38.In sys/extattr.h 39.Sh DESCRIPTION 40Extended attributes allow additional meta-data to be associated 41with vnodes representing files and directories. 42The semantics of this additional data is that of a 43.Dq name=value 44pair, where a name may be defined or undefined, and if defined, 45associated with zero or more bytes of arbitrary binary data. 46Extended attribute names exist within a set of namespaces; each operation 47on an extended attribute is required to provide the namespace to which the 48operation refers. 49If the same name is present in multiple namespaces, the extended attributes 50associated with the names are stored and manipulated independently. 51The following two namespaces are defined universally, although individual 52file systems may implement additional namespaces, or not implement 53these namespaces: 54.Dv EXTATTR_NAMESPACE_USER , 55.Dv EXTATTR_NAMESPACE_SYSTEM . 56The semantics of these attributes are intended to be as follows: user 57attribute data is protected according the normal discretionary 58and mandatory protections associated with the data in the file or 59directory; system attribute data is protected such that appropriate 60privilege is required to directly access or manipulate these attributes. 61.Pp 62Reads of extended attribute data may return specific contiguous regions of 63the meta-data, in the style of 64.Xr VOP_READ 9 , 65but writes will replace the entire current 66.Dq value 67associated with a given name. 68As there are a plethora of file systems with differing extended attributes, 69availability and functionality of these functions may be limited, and they 70should be used with awareness of the underlying semantics of the supporting 71file system. 72Authorization schemes for extended attribute data may also vary by file 73system, as well as maximum attribute size, and whether or not any or 74specific new attributes may be defined. 75.Pp 76Extended attributes are named using a nul-terminated character string. 77Depending on underlying file system semantics, this name may or may not be 78case-sensitive. 79Appropriate vnode extended attribute calls are: 80.Xr VOP_GETEXTATTR 9 , 81.Xr VOP_LISTEXTATTR 9 , 82and 83.Xr VOP_SETEXTATTR 9 . 84.Sh SEE ALSO 85.Xr vfsops 9 , 86.Xr vnodeops 9 87