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Re: [PATCH v2 25/33] block: Make filter drivers use child_of_bds

From: Eric Blake
Subject: Re: [PATCH v2 25/33] block: Make filter drivers use child_of_bds
Date: Wed, 5 Feb 2020 17:02:45 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 2/4/20 11:08 AM, Max Reitz wrote:
Note that some filters have secondary children, namely blkverify (the
image to be verified) and blklogwrites (the log).  This patch does not
touch those children.

I would have guessed blkdebug; but I guess that's not quite a filter for other reasons, so it gets covered in a later patch.

Note that for blkverify, the filtered child should not be format-probed.
While there is nothing enforcing this here, in practice, it will not be:
blkverify implements .bdrv_file_open.  The block layer ensures (and in
fact, asserts) that BDRV_O_PROTOCOL is set for every BDS whose driver
implements .bdrv_file_open.  This flag will then be bequeathed to
blkverify's children, and they will thus (by default) not be probed

("By default" refers to the fact that blkverify's other child (the
non-filtered one) will have BDRV_O_PROTOCOL force-unset, because that is
what happens for all non-filtered children of non-format drivers.)

Signed-off-by: Max Reitz <address@hidden>
  block/blkdebug.c        | 4 +++-
  block/blklogwrites.c    | 3 ++-
  block/blkverify.c       | 4 +++-
  block/copy-on-read.c    | 5 +++--
  block/filter-compress.c | 5 +++--
  block/replication.c     | 3 ++-
  block/throttle.c        | 5 +++--
  7 files changed, 19 insertions(+), 10 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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