1.\"- 2.\" Copyright (c) 1999, 2000, 2001, 2003 Robert N. M. Watson 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.Dd September 5, 2023 27.Dt EXTATTR 9 28.Os 29.Sh NAME 30.Nm extattr 31.Nd virtual file system named extended attributes 32.Sh SYNOPSIS 33.In sys/param.h 34.In sys/vnode.h 35.In sys/extattr.h 36.Sh DESCRIPTION 37Named extended attributes allow additional meta-data to be associated 38with vnodes representing files and directories. 39The semantics of this additional data is that of a "name=value" pair, where 40a name may be defined or undefined, and if defined, associated with zero or 41more bytes of arbitrary binary data. 42Extended attribute names exist within a set of namespaces; each operation 43on an extended attribute is required to provide the namespace to which to 44operation refers. 45If the same name is present in multiple namespaces, the extended attributes 46associated with the names are stored and manipulated independently. 47The following two namespaces are defined universally, although individual 48file systems may implement additional namespaces, or not implement 49these namespaces: 50.Dv EXTATTR_NAMESPACE_USER , 51.Dv EXTATTR_NAMESPACE_SYSTEM . 52The semantics of these attributes are intended to be as follows: user 53attribute data is protected according the normal discretionary 54and mandatory protections associated with the data in the file or 55directory; system attribute data is protected such that appropriate 56privilege is required to directly access or manipulate these attributes. 57By default, processes in a 58.Xr jail 8 59cannot access the system attribute data unless the 60.Va allow.extattr 61configuration parameter is specified. 62.Pp 63Reads of extended attribute data may return specific contiguous regions of 64the meta-data, in the style of 65.Xr VOP_READ 9 , 66but writes will replace the entire current "value" associated with 67a 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 null-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 jail 8 , 86.Xr VFS 9 , 87.Xr VOP_GETEXTATTR 9 , 88.Xr VOP_LISTEXTATTR 9 , 89.Xr VOP_SETEXTATTR 9 90.Sh AUTHORS 91This manual page was written by 92.An Robert Watson . 93.Sh BUGS 94In addition, the interface does not provide a mechanism to retrieve 95the current set of available attributes; it has been suggested that 96providing a 97.Dv NULL 98attribute name should cause a list of defined attributes for the passed file 99or directory, but this is not currently implemented. 100