Re: [Qemu-block] [PATCH] block: Override the driver in the filename with the user-specified one

[Alberto Garcia]

On Mon 24 Aug 2015 08:54:56 PM CEST, Max Reitz wrote:

  [bdrv_fill_options()]
> User-specified options should always have precedence over any other
> option. The thing is, we consider the filename to be specified by the
> user.

For user-specified options like the "lazy-refcounts" case that I
mentioned it makes sense, because that's the way the user wants to open
it.

For the image format it sounds counter-intuitive to me: the format is
already set when the file is opened, the user doesn't have a choice
there, or does she?

> So it is actually correct that this option overrides the @drv
> parameter given to bdrv_open(), because that cannot be set by the user
> and is always set by qemu internally.

Is that really the case?

The drv parameter of bdrv_open() is being set by the user in a number of
places: qmp_drive_backup(), qmp_drive_mirror(), qmp_change_blockdev()
and qemu-img create.

> So I think the problem here is not in bdrv_fill_options(), but rather
> in blockdev.c:external_snapshot_prepare(). This function should not
> pass the driver as the @drv parameter to bdrv_open(), but rather set
> the "driver" option in @options in order to mark this a user-specified
> option.

I guess in that case we should change that in all the other places I
mentioned above.

Berto