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Re: [PATCH 0/4] dm verity: add support for error correction

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On Mon, Nov 09, 2015 at 11:37:35AM -0500, Mike Snitzer wrote:
> I'm left wondering: can the new error correction code be made an
> optional feature that is off by default? -- so as to preserve some
> isolation of this new code from the old dm-verity behaviour.

It's optional in the sense that you must specify error correction
parameters in the table to turn it on. Otherwise, verity_dec_decode
returns -1 and dm-verity handles errors as before.

> might be good to add a wrapper like verity_fec_is_enabled().

Sure. I can do this in v2 and address the other feedback and build
issues as well.

> Also, the 2 other big questions from Mikulas need answering:
> 1) why aren't you actually adjustng error codes, returning success, if
>    dm-verity was able to trap/correct the corruption?

We don't see actual I/O errors very often. Most corruption we've seen
is caused by flaky hardware that doesn't return errors. However, I can
certainly change to code to attempt recovery in this case too.

> 2) please fix the code to preallocate all required memory -- so that
>    verity_fec_alloc_buffers() isn't called in map.

I tried to avoid preallocating the buffers because they are relatively
large (up to 1 MiB depending on the Reed-Solomon parameters) and not
required unless we have errors to correct. I suppose there's no way to
safely do this in the middle of I/O?

> If this error correction feature is going to go upstream we really
> should see any associated userspace enablement also included in
> veritysetup.

I can look into this.

Sami
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[PATCH 0/4] dm verity: add support for error correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-05 03:10 +0100
  [PATCH 1/4] dm verity: clean up duplicate hashing code Sami Tolvanen <samitolvanen@google.com> - 2015-11-05 03:10 +0100
  [PATCH 4/4] dm verity: ignore zero blocks Sami Tolvanen <samitolvanen@google.com> - 2015-11-05 03:10 +0100
  [PATCH 3/4] dm verity: add support for forward error correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-05 03:10 +0100
    Re: [PATCH 3/4] dm verity: add support for forward error correction kbuild test robot <lkp@intel.com> - 2015-11-05 06:40 +0100
  [PATCH 2/4] dm verity: separate function for parsing opt args Sami Tolvanen <samitolvanen@google.com> - 2015-11-05 03:10 +0100
  Re: [PATCH 0/4] dm verity: add support for error correction Milan Broz <mbroz@redhat.com> - 2015-11-05 08:40 +0100
    Re: [PATCH 0/4] dm verity: add support for error correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-05 18:40 +0100
      Re: [PATCH 0/4] dm verity: add support for error correction Mike Snitzer <snitzer@redhat.com> - 2015-11-09 17:40 +0100
        Re: [PATCH 0/4] dm verity: add support for error correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-09 20:20 +0100
          Re: [PATCH 0/4] dm verity: add support for error correction Mike Snitzer <snitzer@redhat.com> - 2015-11-09 21:00 +0100
          Re: [PATCH 0/4] dm verity: add support for error correction Milan Broz <mbroz@redhat.com> - 2015-11-12 11:40 +0100
          Re: [PATCH 0/4] dm verity: add support for error correction Mikulas Patocka <mpatocka@redhat.com> - 2015-11-12 20:00 +0100
    Re: [PATCH 0/4] dm verity: add support for error correction Mikulas Patocka <mpatocka@redhat.com> - 2015-11-06 18:30 +0100
      Re: [PATCH 0/4] dm verity: add support for error correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-06 20:10 +0100
        Re: [dm-devel] [PATCH 0/4] dm verity: add support for error  correction Zdenek Kabelac <zkabelac@redhat.com> - 2015-11-06 20:30 +0100
          Re: [dm-devel] [PATCH 0/4] dm verity: add support for error  correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-06 21:30 +0100
            Re: [dm-devel] [PATCH 0/4] dm verity: add support for error  correction Zdenek Kabelac <zkabelac@redhat.com> - 2015-11-06 22:10 +0100
              Re: [dm-devel] [PATCH 0/4] dm verity: add support for error  correction Sami Tolvanen <samitolvanen@google.com> - 2015-11-06 22:30 +0100
                Re: [dm-devel] [PATCH 0/4] dm verity: add support for error  correction Mikulas Patocka <mpatocka@redhat.com> - 2015-11-07 16:30 +0100
            Re: [dm-devel] [PATCH 0/4] dm verity: add support for error  correction Mikulas Patocka <mpatocka@redhat.com> - 2015-11-07 16:30 +0100
        Re: [PATCH 0/4] dm verity: add support for error correction Mikulas Patocka <mpatocka@redhat.com> - 2015-11-07 16:20 +0100
          Re: [PATCH 0/4] dm verity: add support for error correction Austin S Hemmelgarn <ahferroin7@gmail.com> - 2015-11-09 16:10 +0100

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