From: Eric Blake <eblake@redhat.com>
To: Alberto Garcia <berto@igalia.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>,
qemu-block@nongnu.org, Max Reitz <mreitz@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3 2/4] block: Add 'ignore-backing' field to BlockdevOptionsGenericCOWFormat
Date: Fri, 11 Sep 2015 11:28:04 -0600 [thread overview]
Message-ID: <55F30F24.3000305@redhat.com> (raw)
In-Reply-To: <1be64a26c9a89ff0af4c2b1299d6c8b58361644a.1441890725.git.berto@igalia.com>
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On 09/10/2015 07:39 AM, Alberto Garcia wrote:
> If set to true, the image will be opened with the BDRV_O_NO_BACKING
> flag. This is useful for creating snapshots using images opened with
> blockdev-add, since they are not supposed to have a backing image
> before the operation.
>
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
> block.c | 5 +++++
> qapi/block-core.json | 6 +++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index 22d3b0e..4be32fb 100644
> --- a/block.c
> +++ b/block.c
> @@ -1469,6 +1469,11 @@ static int bdrv_open_inherit(BlockDriverState **pbs, const char *filename,
>
> assert(drvname || !(flags & BDRV_O_PROTOCOL));
>
> + if (qdict_get_try_bool(options, "ignore-backing", false)) {
> + flags |= BDRV_O_NO_BACKING;
> + }
> + qdict_del(options, "ignore-backing");
What happens if the user specified "ignore-backing":true, "backing":...?
Should that be a hard error?
> { 'struct': 'BlockdevOptionsGenericCOWFormat',
> 'base': 'BlockdevOptionsGenericFormat',
> - 'data': { '*backing': 'BlockdevRef' } }
> + 'data': { '*backing': 'BlockdevRef',
> + '*ignore-backing': 'bool' } }
Depending on whether the answer to my question is that we already behave
sanely and don't leave a BlockdevRef dangling if the caller mixes the
two approaches, then:
Reviewed-by: Eric Blake <eblake@redhat.com>
But design-wise, would it make sense to support:
"backing":null
as an explicit request to not open a backing file? Right now, qapi does
not have a way to express 'null' as part of an alternate type; but if it
did, BlockdevRef would merely add 'null' as one of its allowed
alternates. Then we wouldn't need ignore-backing from the QMP
perspective. But I'm still not sure how it would map to the command line
perspective.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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next prev parent reply other threads:[~2015-09-11 17:28 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-10 13:39 [Qemu-devel] [PATCH v3 0/4] Add 'blockdev-snapshot' command Alberto Garcia
2015-09-10 13:39 ` [Qemu-devel] [PATCH v3 1/4] block: rename BlockdevSnapshot to BlockdevSnapshotSync Alberto Garcia
2015-09-11 17:15 ` Max Reitz
2015-09-10 13:39 ` [Qemu-devel] [PATCH v3 2/4] block: Add 'ignore-backing' field to BlockdevOptionsGenericCOWFormat Alberto Garcia
2015-09-11 17:21 ` Max Reitz
2015-09-11 17:28 ` Kevin Wolf
2015-09-11 17:33 ` Max Reitz
2015-09-14 5:54 ` Alberto Garcia
2015-09-14 8:45 ` Kevin Wolf
2015-09-14 14:20 ` Alberto Garcia
2015-09-11 17:28 ` Eric Blake [this message]
2015-09-11 17:30 ` [Qemu-devel] [Qemu-block] " Eric Blake
2015-09-10 13:39 ` [Qemu-devel] [PATCH v3 3/4] block: add a 'blockdev-snapshot' QMP command Alberto Garcia
2015-09-11 17:58 ` Eric Blake
2015-09-14 14:08 ` Alberto Garcia
2015-09-11 18:11 ` Max Reitz
2015-09-10 13:39 ` [Qemu-devel] [PATCH v3 4/4] block: add tests for the 'blockdev-snapshot' command Alberto Garcia
2015-09-11 18:02 ` Eric Blake
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