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Re: [Qemu-block] [PATCH for-next 0/6] qemu-img: Add salvaging mode to co
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH for-next 0/6] qemu-img: Add salvaging mode to convert |
Date: |
Wed, 13 Feb 2019 23:55:07 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 |
Any opinions?
On 03.12.18 18:52, Max Reitz wrote:
> Hi,
>
> This series adds a --salvage option to qemu-img convert. With this,
> qemu-img will not abort when it encounters an I/O error. Instead, it
> tries to narrow it down and will treat the affected sectors as being
> completely 0 (and print a warning).
>
> Testing this is not so easy, because while real I/O errors during read
> operations should be treated as described above, errors encountered
> during bdrv_block_status() should just be ignored and the affected
> sectors should be considered allocated. But blkdebug does not yet have
> a way to intercept this, and:
>
> (1) Just adding a new block-status event would be silly, because I don't
> want an event, I want it to fail on a certain kind of operation, on
> a certain sector range, independently of any events, so why can't we
> just do that? See patch 4.
>
> (2) If we just make blkdebug intercept .bdrv_co_block_status() like all
> other kinds of operations, at least iotest 041 fails, which does
> exactly that silly thing: It uses the read_aio event to wait for any
> read. But it turns out that there may be a bdrv_*block_status()
> call in between, so suddenly the wrong operation yields an error.
> As I said, the real fault here is that it does not really make sense
> to pray that the operation you want to fail is the one that is
> immediately executed after some event that you hope will trigger
> that operation.
> See patch 3.
>
> So patch 3 allows blkdebug users to select which kind of I/O operation
> they actually want to make fail, and patch 4 allows them to not use any
> event, but to have a rule active all the time.
>
> Together, we can then enable error injection for block-status in patch 5
> and make use of event=none iotype=block-status in patch 6.
>
>
> Max Reitz (6):
> qemu-img: Move quiet into ImgConvertState
> qemu-img: Add salvaging mode to convert
> blkdebug: Add @iotype error option
> blkdebug: Add "none" event
> blkdebug: Inject errors on .bdrv_co_block_status()
> iotests: Test qemu-img convert --salvage
>
> qapi/block-core.json | 33 +++++++-
> block/blkdebug.c | 60 ++++++++++++--
> qemu-img.c | 97 ++++++++++++++++------
> qemu-img-cmds.hx | 4 +-
> qemu-img.texi | 5 ++
> tests/qemu-iotests/236 | 164 +++++++++++++++++++++++++++++++++++++
> tests/qemu-iotests/236.out | 43 ++++++++++
> tests/qemu-iotests/group | 1 +
> 8 files changed, 370 insertions(+), 37 deletions(-)
> create mode 100755 tests/qemu-iotests/236
> create mode 100644 tests/qemu-iotests/236.out
>
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