Re: [RFC 3/9] selftests: block_seek_hole: add loop block driver tests

Stefan Hajnoczi
2024-04-03T13:51:53Z

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On Fri, Mar 29, 2024 at 07:38:17AM -0500, Eric Blake wrote:
> On Thu, Mar 28, 2024 at 04:39:04PM -0400, Stefan Hajnoczi wrote:
> > Run the tests with:
> >
> > $ make TARGETS=block_seek_hole -C tools/selftests run_tests
> >
> > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> > ---
> > tools/testing/selftests/Makefile | 1 +
> > .../selftests/block_seek_hole/Makefile | 17 +++
> > .../testing/selftests/block_seek_hole/config | 1 +
> > .../selftests/block_seek_hole/map_holes.py | 37 +++++++
> > .../testing/selftests/block_seek_hole/test.py | 103 ++++++++++++++++++
> > 5 files changed, 159 insertions(+)
> > create mode 100644 tools/testing/selftests/block_seek_hole/Makefile
> > create mode 100644 tools/testing/selftests/block_seek_hole/config
> > create mode 100755 tools/testing/selftests/block_seek_hole/map_holes.py
> > create mode 100755 tools/testing/selftests/block_seek_hole/test.py
> >
>
> > +
> > +def map_holes(fd):
> > + end = os.lseek(fd, 0, os.SEEK_END)
> > + offset = 0
> > +
> > + print('TYPE START END SIZE')
> > +
> > + while offset < end:
> > + contents = 'DATA'
> > + new_offset = os.lseek(fd, offset, os.SEEK_HOLE)
> > + if new_offset == offset:
> > + contents = 'HOLE'
> > + try:
> > + new_offset = os.lseek(fd, offset, os.SEEK_DATA)
> > + except OSError as err:
> > + if err.errno == errno.ENXIO:
> > + new_offset = end
> > + else:
> > + raise err
> > + assert new_offset != offset
> > + print(f'{contents} {offset} {new_offset} {new_offset - offset}')
> > + offset = new_offset
>
> Over the years, I've seen various SEEK_HOLE implementation bugs where
> things work great on the initial boundary, but fail when requested on
> an offset not aligned to the start of the extent boundary. It would
> probably be worth enhancing the test to prove that:
>
> if lseek(fd, offset, SEEK_HOLE) == offset:
> new_offset = lseek(fd, offset, SEEK_DATA)
> assert new_offset > offset
> assert lseek(fd, new_offset - 1, SEEK_HOLE) == new_offset - 1
> else:
> assert lseek(fd, offset, SEEK_DATA) == offset
> new_offset = lseek(fd, offset, SEEK_HOLE)
> assert new_offset > offset
> assert lseek(fd, new_offset - 1, SEEK_DATA) == new_offset - 1
>
> Among other things, this would prove that even though block devices
> generally operate on a minimum granularity of a sector, lseek() still
> gives byte-accurate results for a random offset that falls in the
> middle of a sector, and doesn't accidentally round down reporting an
> offset less than the value passed in to the request.

Sure. I'll add a test for that.

Stefan

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