af_lock(3)						    Attribute Filesystem (AtFS) 						af_lock(3)

NAME

       af_lock, af_unlock, af_testlock - mechanism for reserving update rights in AtFS

SYNOPSIS

       #include <atfs.h>

       Af_user *af_lock (Af_key *aso, Af_user *locker)

       Af_user *af_unlock (Af_key *aso)

       Af_user *af_testlock (Af_key *aso)

DESCRIPTION

       This  manual page describes the interface to the AtFS locking mechanism. Locks are used to avoid conflicting updates to one object history.
       After a user has reserved the update rights, no other user may add new versions to the reserved history.  Reserving the update rights  hap-
       pens  by  locking the most recent version of the history.  As AtFS allows adding new versions to each generation in a history, each genera-
       tion may be locked separately. Reserving update rights for old generations (with generation numbers smaller than the newest generation) are
       performed by locking the most recent version of the corresponding generation.  Removing an ASO (af_rm - manual page af_files(3)) and chang-
       ing an ASO's version number (af_svnum - manual page af_version(3)) also requires a lock on the corresponding ASO.

       af_lock reserves the update permission for the user identified by locker. On  successful  completion,  a  buffer  identical  to	locker	is
       returned, a NULL pointer otherwise.

       af_unlock  cancels  a  formerly established reservation of update rights. Only the owner or the locker of an ASO (identified by the Af_user
       structure that was given to the corresponding call of af_lock) are allowed to do this. On successful completion, af_unlock returns a buffer
       containing the identification of the former locker. This may be empty, if the ASO was not locked.  Upon error, a NULL pointer is returned.

       af_testlock  returns  a	buffer	containing an identification of the current locker of the specified ASO. It returns an empty buffer, if no
       lock is set.

SEE ALSO

       af_version(3), af_files(3)

DIAGNOSTICS

       af_lock and af_unlock return -1 on error and af_errno is set to indicate the error number.

AtFS-1.71						     Fri Jun 25 14:33:11 1993							af_lock(3)