trusty (9) extattr.9freebsd.gz

Provided by: freebsd-manpages_9.2+1-1_all bug

NAME
     extattr — virtual file system named extended attributes


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


DESCRIPTION
     Named extended attributes allow additional meta-data to be associated with vnodes representing files and
     directories.  The semantics of this additional 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 arbitrary binary data.
     Extended attribute names exist within a set of namespaces; each operation on an extended attribute is
     required to provide the namespace to which to 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 protected according
     the normal discretionary and mandatory protections associated 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 null-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
     VFS(9), VFS_EXTATTRCTL(9), VOP_GETEXTATTR(9), VOP_LISTEXTATTR(9), VOP_SETEXTATTR(9)


AUTHORS
     This manual page was written by Robert Watson.


BUGS
     In addition, the interface does not provide a mechanism to retrieve the current set of available
     attributes; it has been suggested that providing a NULL attribute name should cause a list of defined
     attributes for the passed file or directory, but this is not currently implemented.