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Re: [PATCH 1/5] iotests: Update 241 to expose backing layer fragmentatio

From: Vladimir Sementsov-Ogievskiy
Subject: Re: [PATCH 1/5] iotests: Update 241 to expose backing layer fragmentation
Date: Thu, 25 Feb 2021 17:57:26 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1

25.02.2021 16:50, Vladimir Sementsov-Ogievskiy wrote:
18.02.2021 23:15, Eric Blake wrote:
Previous commits (such as 6e280648, 75d34eb9) have mentioned that our
NBD server still sends unaligned fragments when an active layer with
large advertised minimum block size is backed by another layer with a
smaller block size. Expand the test to actually cover these scenario,
by using two different approaches: qcow2 encryption (which forces
512-byte alignment) with an unaligned raw backing file, and blkdebug
with a 4k alignment.

The encryption test passes with the desired results, but only because
the client side works around the server's non-compliance; if you
repeat the test manually with tracing turned on, you will see the
server sending a status for 1000 bytes of data then 1048 bytes of
hole, which is not aligned. But reverting commit 737d3f5244 shows that
it is indeed the client working around the bug in the server.

Meanwhile, the blkdebug test gives incorrect results: remember, when
using x-dirty-bitmap with qemu-img map as a way to sniff alternative
metadata contexts, the meanings of "data" and "zero" are determined by

How I'm tired of this abuse:) It seems that total amount of comments
about it in code and commit messages worth creating more intuitive
interface.. Don't you have an idea in mind?

that context.  Our client workaround is assuming that the fragmented
replies can be merged according to base:allocation rules, but those
rules do not work for other contexts (merging dirty and clean bitmap
should produce dirty; merging allocated and unallocated should produce
allocated; see the FIXME for more about the decoded values we expect).

You could instead keep the test output correct (without FIXME marks) but
add the test to "disabled" group and drop it from the group when fixed.

Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Now I don't think that aligning qemu:allocation-depth information is a correct 
thing to do.

Best regards,

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