NAME    [Toc]    [Back]

     extattr - virtual file system named extended attributes

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     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 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 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) and VOP_SETEXTATTR(9).

AUTHORS    [Toc]    [Back]

     This man page was written by Robert Watson.

BUGS    [Toc]    [Back]

     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.

OpenBSD      3.6                        December     23,     1999