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. If anyone has suggestions how to write this test not xfs specific I would be happy to hear. 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
