Re: [Qemu-devel] [PATCH 5/6] add-cow: support snapshot_blkdev

[Kevin Wolf <kwolf@redhat.com>]

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 <wdongxu@linux.vnet.ibm.com>

Paolo, what do you think about this magic?

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.

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.

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.