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

[Jes Sorensen]

On 12/16/10 12:45, Kevin Wolf wrote:
> Am 16.12.2010 12:04, schrieb address@hidden:
>> From: Jes Sorensen <address@hidden>
>>
>> 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 <address@hidden>
>> ---
>>  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?

It should generate the same code - I kinda liked my style better, but
I'll change it.

>> +    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.

Well if we hit this situation something catastrophic happened. I don't
see how we can continue beyond this point really. The old image was
dropped in the swap and the new one is not accessible ... we're dead :(

Cheers,
Jes