>>we want a open/close consistency in snapshots. > >This depends on the transaction engine in your filesystem. None of the >existing linux filesystems have a way to start a transaction when the >file opens and finish it when the file closes, or a way to roll back >individual operations that have happened inside a given transaction. > >It certainly could be done, but it would also introduce a great deal of >complexity to the FS. And I would be opposed as a matter of architecture to making open/close transactional. People often read more into open/close than is there, but open is just about gaining access and close is just about releasing resources. It isn't appropriate for close to _mean_ anything. There are filesystems that have transactions. They use separate start transaction / end transaction system calls (not POSIX). >> Pausing apps itself >> does not solve this problem, because a file could be already opened >> and in the middle of write. Just to be clear: we're saying "pause," but we mean "quiesce." I.e., tell the application to reach a point where it's not in the middle of anything and then tell you it's there. Indeed, whether you use open/close or some other kind of transaction, just pausing the application doesn't help. If you were to implement open/close transactions, the filesystem driver would just wait for the application to close and in the meantime block all new opens. -- Bryan Henderson IBM Almaden Research Center San Jose CA Filesystems - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
