On Mon, Oct 29, 2018 at 09:43:40AM +0000, fdmanana@xxxxxxxxxx wrote: > From: Filipe Manana <fdmanana@xxxxxxxx> > > Unless the '-s' option is passed to fssum, it should not detect file holes > and have their existence influence the computed checksum for a file. This > tool was added to test btrfs' send/receive feature, so that it checks for > any metadata and data differences between the original filesystem and the > filesystem that receives send streams. > > For a long time the test btrfs/007, which tests btrfs' send/receive with > fsstress, fails sporadically reporting data differences between files. > However the md5sum/sha1sum from the reported files in the original and > new filesystems are the same. The reason why fssum fails is because even > in normal mode it still accounts for number of holes that exist in the > file and their respective lengths. This is done using the SEEK_DATA mode > of lseek. The btrfs send feature does not preserve holes nor prealloc > extents (not supported by the current protocol), so whenever a hole or > prealloc (unwritten) extent is detected in the source filesystem, it > issues a write command full of zeroes, which will translate to a regular > (written) extent in the destination filesystem. This is why fssum reports > a different checksum. A prealloc extent also counts as hole when using > lseek. > > For example when passing a seed of 1540592967 to fsstress in btrfs/007, > the test fails, as file p0/d0/f7 has a prealloc extent in the original > filesystem (in the incr snapshot). > > Fix this by making fssum just read the hole file and feed its data to the > digest calculation function when option '-s' is not given. If we ever get > btrfs' send/receive to support holes and fallocate, we can just change > the test and pass the '-s' option to all fssum calls. > > Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Thanks, Josef
