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EXTATTR(9) NetBSD Kernel Developer's Manual EXTATTR(9)
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extattr -- file system extended attributes
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, availabil-
ity 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).
NetBSD 8.1 January 2, 2005 NetBSD 8.1