96 lines
4.1 KiB
Groff
96 lines
4.1 KiB
Groff
.\"-
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.\" Copyright (c) 1999, 2000, 2001, 2003 Robert N. M. Watson
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd December 23, 1999
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.Os
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.Dt EXTATTR 9
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.Sh NAME
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.Nm extattr
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.Nd virtual file system named extended attributes
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/vnode.h
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.In sys/extattr.h
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.Sh DESCRIPTION
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Named extended attributes allow additional meta-data to be associated
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with vnodes representing files and directories.
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The semantics of this additional data is that of a "name=value" pair, where
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a name may be defined or undefined, and if defined, associated with zero or
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more bytes of arbitrary binary data.
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Extended attribute names exist within a set of namespaces; each operation
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on an extended attribute is required to provide the namespace to which to
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operation refers.
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If the same name is present in multiple namespaces, the extended attributes
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associated with the names are stored and manipulated independently.
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The following two namespaces are defined universally, although individual
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file systems may implement additional namespaces, or not implement
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these namespaces:
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.Dv EXTATTR_NAMESPACE_USER ,
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.Dv EXTATTR_NAMESPACE_SYSTEM .
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The semantics of these attributes are intended to be as follows: user
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attribute data is protected according the normal discretionary
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and mandatory protections associated with the data in the file or
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directory; system attribute data is protected such that appropriate
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privilege is required to directly access or manipulate these attributes.
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.Pp
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Reads of extended attribute data may return specific contiguous regions of
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the meta-data, in the style of
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.Xr VOP_READ 9 ,
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but writes will replace the entire current "value" associated with
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a given name.
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As there are a plethora of file systems with differing extended attributes,
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availability and functionality of these functions may be limited, and they
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should be used with awareness of the underlying semantics of the supporting
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file system.
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Authorization schemes for extended attribute data may also vary by file
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system, as well as maximum attribute size, and whether or not any or
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specific new attributes may be defined.
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.Pp
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Extended attributes are named using a null-terminated character string.
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Depending on underlying file system semantics, this name may or may not be
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case-sensitive. Appropriate vnode extended attribute calls are:
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.Xr VOP_GETEXTATTR 9 ,
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.Xr VOP_LISTEXTATTR 9 ,
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and
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.Xr VOP_SETEXTATTR 9 .
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.Sh SEE ALSO
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.Xr VFS 9 ,
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.Xr VFS_EXTATTRCTL 9 ,
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.Xr VOP_GETEXTATTR 9 ,
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.Xr VOP_LISTEXTATTR 9 ,
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.Xr VOP_SETEXTATTR 9
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.Sh AUTHORS
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This man page was written by
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.An Robert Watson .
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.Sh BUGS
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In addition, the interface does not provide a mechanism to retrieve
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the current set of available attributes; it has been suggested that
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providing a
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.Dv NULL
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attribute name should cause a list of defined attributes for the passed file
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or directory, but this is not currently implemented.
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