Re: [PATCH v2 2/3] generic/574: corrupt btrfs merkle tree data

Eric Biggers
2021-04-08T23:16:32Z

On Thu, Apr 08, 2021 at 11:49:37AM -0700, Boris Burkov wrote:
> On Thu, Apr 08, 2021 at 11:41:42AM -0700, Eric Biggers wrote:
> > On Thu, Apr 08, 2021 at 11:30:12AM -0700, Boris Burkov wrote:
> > >
> > > Note that there is a bit of a kludge here: since btrfs_corrupt_block
> > > doesn't handle streaming corruption bytes from stdin (I could change
> > > that, but it feels like overkill for this purpose), I just read the
> > > first corruption byte and duplicate it for the desired length. That is
> > > how the test is using the interface in practice, anyway.
> >
> > If that's the problem, couldn't you just write the data to a temporary file?
>
> Sorry, I was a bit too vague. It doesn't have a file or stdin interface,
> as far as I know.
>
> btrfs-corrupt-block has your typical "kitchen sink of flags" interface and
> doesn't currently read input from streams/files. I extended that
> interface in the simplest way to support arbitrary corruption, which
> didn't fit with the stream based corruption this test does.
>
> my options seem to be:
> shoehorn the "byte, length" interface into this test or
> shoehorn the "stream corruption input in" interface into
> btrfs-corrupt-block.
>
> I have no problem with either, the former was just less work because I
> already wrote it that way. If the junk I did here is a deal-breaker, I
> don't mind modifying btrfs-corrupt-block.
>

If it's a lot of trouble to handle arbitrary data, then I think you should
change _fsv_scratch_corrupt_merkle_tree() to actually take a (byte, length) pair
instead of data on stdin. Otherwise, _fsv_scratch_corrupt_merkle_tree() would
claim to do one thing but actually would do a different thing on one specific
filesystem.

- Eric