Re: [Qemu-block] [PATCH v3 6.5/6] nbd/client: Trace server noncompliance on structured reads

[Vladimir Sementsov-Ogievskiy]

30.03.2019 19:53, Eric Blake wrote:
> Just as we recently added a trace for a server sending block status
> that doesn't match the server's advertised minimum block alignment,
> let's do the same for read chunks.  But since qemu 3.1 is such a
> server (because it advertised 512-byte alignment, but when serving a
> file that ends in data but is not sector-aligned, NBD_CMD_READ would
> detect a mid-sector change between data and hole at EOF and the
> resulting read chunks are unaligned), we don't want to change our
> behavior of otherwise tolerating unaligned reads.
> 
> Note that even though we fixed the server for 4.0 to advertise an
> actual block alignment (which gets rid of the unaligned reads at EOF
> for posix files), we can still trigger it via other means:
> 
> $ qemu-nbd --image-opts 
> driver=blkdebug,align=512,image.driver=file,image.filename=/path/to/non-aligned-file
> 
> Arguably, that is a bug in the blkdebug block status function, for
> leaking a block status that is not aligned. It may also be possible to
> observe issues with a backing layer with smaller alignment than the
> active layer, although so far I have been unable to write a reliable
> iotest for that scenario.
> 
> Signed-off-by: Eric Blake <address@hidden>

Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>



-- 
Best regards,
Vladimir