On Wed, Apr 23, 2008 at 09:23:03AM -0400, Chris Mason wrote: > On Wednesday 23 April 2008, Evgeniy Polyakov wrote: > > On Wed, Apr 23, 2008 at 09:07:28AM -0400, Chris Mason > (chris.mason@xxxxxxxxxx) wrote: > > > But, userland expects things not to be undone. Picture two procs > > > operating in a directory. One proc calls fsync and gets assurance from > > > the FS that things are on disk. The other proc calls rollback and undoes > > > the fsync. The posix API isn't built around this. > > > > Rollback happens on transaction, so first application called fsync in > > own trasaction, which flushed data to disk, while second thread has own > > trasaction, and that data will be removed, while data written in first > > transaction is still on disk. > > The kind of logging this requires is outside the scope of Btrfs ;) It is > possible if both procs are running in different tree roots, but how about: > > proc A: mkdir dir1 > proc A: create dir1/file1 > proc B: add data to dir1/file1 > proc B: fsync dir1/file1 > proc A: rollback > > Filesystems can be databases, but not with the current APIs. Userland simply > isn't built around these semantics today. proc A: mkdir dir1 proc A: create dir1/file1 proc B: add data to dir1/file1 proc B: fsync dir1/file1 proc A: unlink dir1/file1 proc A: rmdir dir1 I don't see the difference. Bron. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
