These functions implement a simple transaction mechanism for AtFS.
A transaction starts with calling af_transaction. All changes to
existing ASOs performed hereafter have no immediate permanent effect.
They rather get into effect, when the transaction is ended.
Calling af_commit ends the transactions and causes all changes to
be saved to disk. af_abort aborts the transaction without saving
the changes. These will then be discarded.
Only modification of the state of existing source ASOs will be
deferred. Creation or deletion of ASOs have immediate effect,
regardless if a transaction is in effect or not. Additionally, all
operations on derived ASOs (all operations on the derived object
cache) are not affected by the transaction.
All archive files that are to be changed when the transaction is
finished are locked until the end of the transaction.
The lock prevents all other applications to perform any modifications
on the archive file. You should make sure, that ending a transaction
should never be dependent on the successful termination of another
application (deadlock danger).
DIAGNOSTICS
Upon error, -1 is returned
and af_errno is set to the corresponding error number.
BUGS
Changes to the contents of busy versions have immediate effect.