[Qemu-devel] Re: [PATCH 2/3] Introduce do_snapshot_blkdev() and monitor command to handle it.

[Kevin Wolf <kwolf@redhat.com>]

Am 16.12.2010 12:04, schrieb Jes.Sorensen@redhat.com:
> From: Jes Sorensen <Jes.Sorensen@redhat.com>
> 
> The monitor command is:
> snapshot_blkdev <device> [snapshot-file] [format]
> 
> Default format is qcow2. For now snapshots without a snapshot-file, eg
> internal snapshots, are not supported.
> 
> Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
> ---
>  blockdev.c      |   61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  blockdev.h      |    1 +
>  hmp-commands.hx |   19 +++++++++++++++++
>  3 files changed, 81 insertions(+), 0 deletions(-)
> 
> diff --git a/blockdev.c b/blockdev.c
> index 3b3b82d..9d6f72c 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -516,6 +516,67 @@ void do_commit(Monitor *mon, const QDict *qdict)
>      }
>  }
>  
> +int do_snapshot_blkdev(Monitor *mon, const QDict *qdict, QObject **ret_data)
> +{
> +    const char *device = qdict_get_str(qdict, "device");
> +    const char *filename = qdict_get_try_str(qdict, "snapshot_file");
> +    const char *format = qdict_get_try_str(qdict, "format");
> +    const char format_qcow2[] = "qcow2";
> +    BlockDriverState *bs;
> +    BlockDriver *drv, *proto_drv;
> +    int ret = 0;
> +    int flags;
> +
> +    bs = bdrv_find(device);
> +    if (!bs) {
> +        qerror_report(QERR_DEVICE_NOT_FOUND, device);
> +        ret = -1;
> +        goto out;
> +    }
> +
> +    if (!format) {
> +        format = format_qcow2;

Why introducing format_qcow2 instead of directly using the string
literal here?

> +    }
> +
> +    drv = bdrv_find_format(format);
> +    if (!drv) {
> +        qerror_report(QERR_INVALID_BLOCK_FORMAT, format);
> +        ret = -1;
> +        goto out;
> +    }
> +
> +    proto_drv = bdrv_find_protocol(filename);
> +    if (!proto_drv) {
> +        qerror_report(QERR_INVALID_BLOCK_FORMAT, format);
> +        ret = -1;
> +        goto out;
> +    }
> +
> +    ret = bdrv_img_create(filename, format, bs->filename,
> +                          bs->drv->format_name, NULL, -1, bs->open_flags);
> +    if (ret) {
> +        goto out;
> +    }
> +
> +    qemu_aio_flush();
> +    bdrv_flush(bs);
> +
> +    flags = bs->open_flags;
> +    bdrv_close(bs);
> +    ret = bdrv_open(bs, filename, flags, drv);
> +    /*
> +     * If reopening the image file we just created fails, we really
> +     * are in trouble :(
> +     */
> +    assert(ret == 0);

bdrv_commit handles this case by setting bs->drv = NULL. After this the
device will fail all requests with -ENOMEDIUM, but at least you don't
lose your VM immediately.

Kevin