On Tue, Mar 05, 2019 at 07:39:28AM +0200, Amir Goldstein wrote: > On Tue, Mar 5, 2019 at 2:50 AM Dave Chinner <david@xxxxxxxxxxxxx> 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. This says: - ftruncate A - rename A B - fsync B > > > 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... > > > > 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... > > > > That is not what is happening in Filipe's test. Test has: > - ftruncate A > - fsync A > - rename A B > - fsync B And this does not match the test description. /me goes and looks at the test again to check. Ok, the test is as Filipe describes: - pwrite 0 0x8000 A - fsync A - truncate 3000 A - rename A B - fsync B There is no fsync between truncate and rename. > So the reason this is working is because 2nd fsync needs to > persist ctime of B and not because it needs to persist the > truncate. ctime modifications during rename are irrelevent because there's no fsync between the truncate and the rename so the file inode is already dirty due to the truncate. I think you've got the wrong end of the stick here, Amir. :) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
