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.

Debian                                          December 23, 1999                                     EXTATTR(9)