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EXTATTR(9)		 BSD Kernel Developer's Manual		    EXTATTR(9)

NAME
     extattr — file system extended attributes

SYNOPSIS
     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <sys/extattr.h>

DESCRIPTION
     Extended attributes allow additional meta-data to be associated with
     vnodes representing files and directories.	 The semantics of this addi‐
     tional 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 arbi‐
     trary binary data.	 Extended attribute names exist within a set of names‐
     paces; each operation on an extended attribute is required to provide the
     namespace to which the operation refers.  If the same name is present in
     multiple namespaces, the extended attributes associated with the names
     are stored and manipulated independently.	The following two namespaces
     are defined universally, although individual file systems may implement
     additional namespaces, or not implement these namespaces:
     EXTATTR_NAMESPACE_USER, EXTATTR_NAMESPACE_SYSTEM.	The semantics of these
     attributes are intended to be as follows: user attribute data is pro‐
     tected according the normal discretionary and mandatory protections asso‐
     ciated with the data in the file or directory; system attribute data is
     protected such that appropriate privilege is required to directly access
     or manipulate these attributes.

     Reads of extended attribute data may return specific contiguous regions
     of the meta-data, in the style of 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.

     Extended attributes are named using a nul-terminated character string.
     Depending on underlying file system semantics, this name may or may not
     be case-sensitive.	 Appropriate vnode extended attribute calls are:
     VOP_GETEXTATTR(9), VOP_LISTEXTATTR(9), and VOP_SETEXTATTR(9).

SEE ALSO
     vfsops(9), vnodeops(9)

BSD				January 2, 2005				   BSD

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