extattr(9) - FreeBSD 15.1-RELEASE and Ports.quarterly Manual Pages

home | help
EXTATTR(9)		    Kernel Developer's Manual		      EXTATTR(9)

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  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  arbitrary
     binary  data.   Extended  attribute names exist within a set of namespaces;
     each operation on an extended attribute is required to  provide  the  name-
     space  to which to operation refers.  If the same name is present in multi-
     ple namespaces, the extended  attributes  associated  with  the  names  are
     stored and manipulated independently.  The following two namespaces are de-
     fined  universally,  although  individual	file systems may implement addi-
     tional    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 manipu-
     late these attributes.  By default, processes in a  jail(8)  cannot  access
     the  system attribute data unless the allow.extattr configuration parameter
     is specified.

     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 en-
     tire current "value" associated with a given name.  As there are a plethora
     of  file systems with differing extended attributes, availability and func-
     tionality of these functions may be limited, and they should be  used  with
     awareness	of  the underlying semantics of the supporting file system.  Au-
     thorization schemes for extended attribute data may also vary by file  sys-
     tem,  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_GETEX-
     TATTR(9), VOP_LISTEXTATTR(9), and VOP_SETEXTATTR(9).

SEE ALSO
     jail(8), VFS(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.

FreeBSD 15.1			September 5, 2023		      EXTATTR(9)
Want to link to this manual page? Use this URL:
<https://man.FreeBSD.org/cgi/man.cgi?query=extattr&sektion=9&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>
home | help