On Tue, Mar 05, 2019 at 11:50:20AM +1100, Dave Chinner wrote: > On Mon, Mar 04, 2019 at 05:04:23PM +0200, Amir Goldstein wrote: > > On Mon, Mar 4, 2019 at 4:44 PM <fdmanana@xxxxxxxxxx> wrote: > > > > > > From: Filipe Manana <fdmanana@xxxxxxxx> > > > > > > Test that if we truncate a file to reduce its size, rename it and then > > > fsync it, after a power failure the file has a correct size and name. > > > > > > > I am not sure that ext4/xfs semantics guaranty anything about > > persisting file name after fsync of file?... > > They do. It's that pesky "strictly ordered metadata" thing I keep > having to explain to people... https://marc.info/?l=fstests&m=155010885626284&w=2 -Dave. > > i.e. if you fsync an inode, then you are persisting all the changes > needed to reference that file and it's data. And so if there was a > rename in the history of that file, then that is persisted, too. > Which means that both the original and the new directory > modifications are persisted, too. > > *POSIX* doesn't require this - it says that if you O_DSYNC data, > then it also includes all the metadata needed to reference that > data. So even if the data is there, POSIX doesn't define whether the > rename is there or noti, just that you can get to the fsync'd data > via either the old or new name. IOWs, POSIX allows the behaviour to > be implementation specific. > > In this case, file systems with strictly ordered metadata will end > up making the rename visible because the rename occurred before the > truncate that the fsync() is persisting... > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx > -- Dave Chinner david@xxxxxxxxxxxxx
