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Re: [Qemu-block] [PATCH v2 0/2] block/file-posix: Fix unaligned O_DIRECT

From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH v2 0/2] block/file-posix: Fix unaligned O_DIRECT block status
Date: Mon, 20 May 2019 15:25:31 +0200
User-agent: Mutt/1.11.3 (2019-02-01)

Am 15.05.2019 um 06:15 hat Max Reitz geschrieben:
> The user-visible problem:
> $ echo > foo
> $ qemu-img map --image-opts driver=file,filename=foo,cache.direct=on
> Offset          Length          Mapped to       File
> qemu-img: block/io.c:2093: bdrv_co_block_status: Assertion `*pnum &&
> QEMU_IS_ALIGNED(*pnum, align) && align > offset - aligned_offset'
> failed.
> The internal problem: file-posix truncates status requests to the EOF.
> If the EOF is not aligned at the request_alignment,
> bdrv_co_block_status() won't like that.
> See patch 1 for a deeper discussion (including two possible alternatives
> how we could address the problem).
> (As I note there, I’ve looked through all block drivers, and I didn’t
> find any other which could have the same problem.  gluster uses the same
> block-status code, but it doesn’t set a request_alignment.  NBD
> force-aligns the server response in nbd_parse_blockstatus_payload().
> qcow2... Should be fine as long as no crypto driver has a block limit
> exceeding the qcow2 cluster size.  And so on.)
> Patch 2 adds a test.  After writing that test, I noticed that we already
> had one: 109 fails with -c none before patch 1.  Er, well, at least the
> new test is more succinct and has the correct default cache mode, so it
> will actually do the test if you run ./check without enforcing any cache
> on a filesystem that supports O_DIRECT.

Thanks, applied to the block branch.


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