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Re: [Qemu-devel] [PATCH 5/6] add-cow: support snapshot_blkdev
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 5/6] add-cow: support snapshot_blkdev |
Date: |
Thu, 14 Jun 2012 13:18:56 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 |
Il 14/06/2012 12:59, Kevin Wolf ha scritto:
> Am 13.06.2012 16:36, schrieb Dong Xu Wang:
>> add-cow will let raw file support snapshot_blkdev indirectly.
>>
>> Signed-off-by: Dong Xu Wang <address@hidden>
>
> Paolo, what do you think about this magic?
Besides the obvious layering violation (it would be better to add a new
method bdrv_ext_snapshot_create perhaps) I don't see very much a problem
in it. Passing image creation options sounds like a good idea that we
can add in the future as an extension.
But honestly, I don't really see the point of add-cow in general... The
raw image is anyway not usable without a pass through qemu-io convert,
and mirroring will also allow collapsing an image to raw (with the
persistent dirty bitmap playing the role of the add-cow metadata).
> I think I can see its use especially for HMP because it's quite
> convenient, but on the other hand it assumes a fixed image path for the
> new raw image. This isn't going to work for block devices, for example.
True, but then probably you would use mode='existing', because you need
to pre-create the logical volume.
> If we don't do it this way, we need to allow passing image creation
> options to the snapshotting command so that you can pass a precreated
> image file.
This sounds like a useful extension anyway, except that passing an
unstructured string for image creation options is ugly... Perhaps we
can base a better implementation of options on Laszlo's QemuOpts visitor.
Paolo
>
> Kevin
>
>> ---
>> blockdev.c | 31 +++++++++++++++++++++++++++----
>> docs/live-block-ops.txt | 10 +++++++++-
>> 2 files changed, 36 insertions(+), 5 deletions(-)
>>
>> diff --git a/blockdev.c b/blockdev.c
>> index 622ecba..2d89e5e 100644
>> --- a/blockdev.c
>> +++ b/blockdev.c
>> @@ -783,15 +783,38 @@ void qmp_transaction(BlockdevActionList *dev_list,
>> Error **errp)
>>
>> /* create new image w/backing file */
>> if (mode != NEW_IMAGE_MODE_EXISTING) {
>> - ret = bdrv_img_create(new_image_file, format,
>> + if (strcmp(format, "add-cow")) {
>> + ret = bdrv_img_create(new_image_file, format,
>> states->old_bs->filename,
>> states->old_bs->drv->format_name,
>> NULL, -1, flags);
>> - if (ret) {
>> - error_set(errp, QERR_OPEN_FILE_FAILED, new_image_file);
>> - goto delete_and_fail;
>> + } else {
>> + char image_file[1024];
>> + char option[1024];
>> + uint64_t size;
>> +
>> + bdrv_get_geometry(states->old_bs, &size);
>> + size *= BDRV_SECTOR_SIZE;
>> +
>> + sprintf(image_file, "%s.raw", new_image_file);
>> +
>> + ret = bdrv_img_create(image_file, "raw", NULL,
>> + NULL, NULL, size, flags);
>> + if (ret) {
>> + error_set(errp, QERR_UNDEFINED_ERROR);
>> + return;
>> + }
>> + sprintf(option, "image_file=%s.raw", new_image_file);
>> + ret = bdrv_img_create(new_image_file, format,
>> + states->old_bs->filename,
>> + states->old_bs->drv->format_name,
>> + option, -1, flags);
>> }
>> }
>> + if (ret) {
>> + error_set(errp, QERR_OPEN_FILE_FAILED, new_image_file);
>> + goto delete_and_fail;
>> + }
>>
>> /* We will manually add the backing_hd field to the bs later */
>> states->new_bs = bdrv_new("");
>> diff --git a/docs/live-block-ops.txt b/docs/live-block-ops.txt
>> index a257087..c97344b 100644
>> --- a/docs/live-block-ops.txt
>> +++ b/docs/live-block-ops.txt
>> @@ -2,7 +2,8 @@ LIVE BLOCK OPERATIONS
>> =====================
>>
>> High level description of live block operations. Note these are not
>> -supported for use with the raw format at the moment.
>> +supported for use with the raw format at the moment, but we can use
>> +add-cow as metadata to suport raw format.
>>
>> Snapshot live merge
>> ===================
>> @@ -56,3 +57,10 @@ into that image. Example:
>> (qemu) block_stream ide0-hd0
>>
>>
>> +
>> +Raw is not supported, but we can use add-cow in the 1st step:
>> +
>> +(qemu) snapshot_blkdev ide0-hd0 /new-path/disk.img add-cow
>> +
>> +It will create a raw file named disk.img.raw, with the same virtual size of
>> +ide0-hd0 first, and then create disk.img.
>
>
>
- Re: [Qemu-devel] [PATCH 4/6] qemu-img: add-cow will not support convert, (continued)
[Qemu-devel] [PATCH 3/6] add-cow file format, Dong Xu Wang, 2012/06/13
[Qemu-devel] [PATCH 6/6] add-cow: support qemu-iotests, Dong Xu Wang, 2012/06/13
[Qemu-devel] [PATCH 5/6] add-cow: support snapshot_blkdev, Dong Xu Wang, 2012/06/13
Re: [Qemu-devel] [PATCH 1/6 v10] docs: spec for add-cow file format, Eric Blake, 2012/06/13