On Fri, Jan 20, 2017 at 10:49:07AM +0200, Amir Goldstein wrote: > On Thu, Jan 19, 2017 at 2:13 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > Miklos, > > > > I implemented freeze/thaw of overlayfs, because I need it for > > overlay snapshots (CoW decision is made before mnt_wat_write(upper) > > and I need to serialize it with snapshot take). > > > > Not sure if there are other use cases for overlayfs freeze?? > > > > Tested freeze stress with xfstest generic/068 generic/390. > > > > While staring at the code, I realized that syncfs(2) for overlayfs > > seems broken. It looks like only inodes are synced and upper fs > > metadata is not being flushed, but I could be wrong. > > > > Tested sync sanity with -g quick (although no test calls syncfs directly). > > Tested the usual unionmount sanity over xfs and over tmpfs. > > > > I am not sure exactly how to write a test case to verify this alleged > > breakage? > > > > Well, I have a smoking gun. > Wrote this xfs specific test, which checks xfs stats after syncfs/fsync: > https://github.com/amir73il/overlayfs/blob/master/tests/xfs_syncfs.sh > > Good (on xfs 4.10.0-rc4): > # ./syncfs.sh /base/ > before touch > xfs_log_force = 375 > after touch > xfs_log_force = 375 > after syncfs > xfs_log_force = 376 > after fsync > xfs_log_force = 376 > after fsync #2 > xfs_log_force = 376 > > Bad (on overlayfs 4.10.0-rc4): > # ./syncfs.sh /mnt > before touch > xfs_log_force = 376 > after touch > xfs_log_force = 376 > after syncfs > xfs_log_force = 376 > after fsync > xfs_log_force = 377 > after fsync #2 > xfs_log_force = 377 > > Overlayfs syncfs fails to flush the xfs log. > > I'll see if I can put this test into xfstests. > I am going to need some sort of require_upper_fs_is_xfs > not sure id it already exists. There's no such _require rules in xfstests yet. > > If anyone has suggestions how to write this test not xfs specific I > would be happy to hear. > Eryu? Sorry, I have no idea right now.. Eryu > > Also, FYI, xfs_io -c syncfs is broken. > Going to send a fix patch soon. -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
