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 happens by locking the most recent version of the history.  As AtFS  allows  adding
       new  versions  to  each generation in a history, each generation 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  changing  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.