On Fri, Dec 1, 2017 at 11:43 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > On Fri, Dec 01, 2017 at 09:21:15AM +0200, Amir Goldstein wrote: [...] >> >> Anyway, I see people are not so fond of the delalloc "canary test". >> Perhaps a still simple and quick test would be to do small buffered >> write; sync; small direct io read? > > No, because the direct IO read can flush dirty buffers across the > range the IO is being done on. IOWs, you don't know if the sync > actually flushed it, the direct IO read flushed it, or the direct IO > read fell back to buffered IO and simply read the in memory copy. > > Let's step back a moment: What bug/regression are you actually > trying to expose/reproduce here? The overlayfs bug (not regression) that Chengguang reported and posted a fix for - syncfs on overlayfs doesn't flush dirty inodes: https://marc.info/?l=linux-unionfs&m=151192099131198&w=2 > Why is it not already covered by at > least one of the other generic sync/fsync tests we already have? > Because there are zero "syncfs" tests. AFAIK, "fsync" is not broken on overlayfs, because it operated on the real underlying inode and "sync" is not a problem, because dirty underlying inodes will be flushed by sync_filesystem() of the underlying fs. Still, I recommended that Chengguang's test, whichever method is chosen, will be generic and cover all those sync variants. If I would to write a generic syncfs test for a blockdev fs, I would have chosen to _mount_flakey, call _flakey_drop_and_remount after syncfs and examine compare md5sum of the written file. Alas, overlayfs is not a blockdev fs, so using the flakey helpers as is the generic test won't run on overlayfs. It is possible to write an overlayfs specific test, which sets up a dm-flakey target over a loop device and uses that fs as the overlayfs upper fs, but then the test won't be generic. If you think we should go for non-generic overlayfs test, that is fine by me. If you have a clever idea how to write a generic "syncfs" test that would also apply to non blockdev fs, please do share it, because *that* was the requirement that lead me to the "delalloc canary" test. Thanks, Amir. -- To unsubscribe from this list: send the line "unsubscribe fstests" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
