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Re: [Qemu-block] [Qemu-devel] [PATCH v2 3/3] block: add default implemen

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 3/3] block: add default implementations for bdrv_co_get_block_status()
Date: Mon, 3 Jul 2017 12:51:45 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0

On 07/03/2017 11:12 AM, Eric Blake wrote:
> On 06/29/2017 01:43 PM, Manos Pitsidianakis wrote:
>> bdrv_co_get_block_status_from_file() and
>> bdrv_co_get_block_status_from_backing() set *file to bs->file and
>> bs->backing respectively, so that bdrv_co_get_block_status() can recurse
>> to them. Future block drivers won't have to duplicate code to implement
>> this.
>> Reviewed-by: Stefan Hajnoczi <address@hidden>
>> Signed-off-by: Manos Pitsidianakis <address@hidden>
>> ---
>>  block/blkdebug.c          | 12 +-----------
>>  block/commit.c            | 12 +-----------
>>  block/io.c                | 24 ++++++++++++++++++++++++
>>  block/mirror.c            | 12 +-----------
>>  include/block/block_int.h | 16 ++++++++++++++++
>>  5 files changed, 43 insertions(+), 33 deletions(-)
> My [still-needs-rebasing] part 3 series converting
> bdrv_co_get_block_status to byte-based will be impacted by this, but I'd
> rather yours go in first and I can deal with the rebase fallout.

In fact, my rebase fallout is to completely delete
bdrv_co_get_block_status_from_file().  Why? Because blkdebug is the only
client, but I want to enhance blkdebug to add in-place assert()ions that
the values passed by the block layer are properly aligned to
bs->bl.request_alignment (matching what blkdebug does for read and write
- after all, if a device cannot access smaller than a given alignment
for a read, it should not be able to report different statuses half-way
through that granularity).  However, in-place assertions are no longer
generic, so we no longer have a client of a generic helper function
referring to bs->file.

Which means you are REALLY left only with commit and mirror as the two
functions that have a common implementation of pointing back to backing.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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