From: Alberto Garcia <berto@igalia.com>
To: Eric Blake <eblake@redhat.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 3/4] block: add a 'blockdev-snapshot' QMP command
Date: Mon, 14 Sep 2015 16:08:07 +0200 [thread overview]
Message-ID: <w51lhc9gkl4.fsf@maestria.local.igalia.com> (raw)
In-Reply-To: <55F31633.6010800@redhat.com>
On Fri 11 Sep 2015 07:58:11 PM CEST, Eric Blake wrote:
>> +void qmp_blockdev_snapshot(const char *device, const char *snapshot,
>> + Error **errp)
>> +{
>> + BlockdevSnapshot snapshot_data = {
>> + .device = (char *) device,
>> + .snapshot = (char *) snapshot
>> + };
>
> Hmm. Sounds like you'd love to use my pending 'box':true qapi glue to
> make this function have the saner signature of
>
> void qmp_blockdev_snapshot(BlockdevSnapshot *arg, Error **errp);
>
> rather than having to rebuild the struct yourself (with an annoying
> cast to lose const) :)
> https://lists.gnu.org/archive/html/qemu-devel/2015-09/msg02599.html
That's cool! We can simplify this later as you suggest.
>> +Create a snapshot, by installing 'device' as the backing image of
>> +'snapshot'. Additionally, if 'device' is associated with a block
>> +device, the block device changes to using 'snapshot' as its new
>> +active image.
>
> Still didn't answer the question from the earlier review of whether
> the blockdev-snapshot-sync behavior of specifying the node name of an
> active layer in order to not pivot the block device to the snapshot
> still makes sense to support in the blockdev-snapshot case.
Sorry if I overlooked the explanation, but I still didn't get the use
case for this.
And particularly for this command, that doesn't create any image but
simply uses a previously-opened one.
What would 'pivot': false do ? As far as I can see, specifying the node
name of an active layer in blockdev-snapshot-sync seems to pivot the
block device to the snapshot.
{ "execute": "blockdev-snapshot-sync",
"arguments": { "node-name": "hd0",
"snapshot-file": "hd1.qcow2",
"snapshot-node-name": "hd1" } }
(qemu) info block
virtio0 (hd1): hd1.qcow2 (qcow2)
Cache mode: writeback
Backing file: hd0.qcow2 (chain depth: 1)
Berto
next prev parent reply other threads:[~2015-09-14 14:08 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
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 [this message]
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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