Re: [PATCH] fstests: fix fssum to actually ignore file holes when supposed to

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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



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