Re: [Qemu-devel] [PATCH] qemu-io: add flag to mark files growable

[Kevin Wolf <kwolf@redhat.com>]

Christoph Hellwig schrieb:
> On Mon, Jul 06, 2009 at 10:53:53AM +0200, Kevin Wolf wrote:
>> Christoph Hellwig schrieb:
>>> Add a -g flag to the open command and the main qemu-io command line to
>>> allow opening a file growable.  This is only allowed for protocols,
>>> mirroring the limitation exposed through bdrv_file_open.
>> This limitation doesn't look quite right. I'm not sure if growable
>> images are used anywhere else, too, but their main usage is for the
>> image file access in formats like qcow - that is, growable images are
>> usually raw. And raw didn't have a protocol name until recently.
> 
> It does have a protocol now, and the way current qemu is implemented
> growable is only set from bdrv_file_open, which implies the BDRV_O_FILE
> argument to bdrv_open2, which means we use find_protocol to find the
> BlockDriver and find_protocol needs protocol_name set.
> 
> If you want to backport this patch to a qemu version that doesn't
> have a protocol_name for raw you'll have to adjust it to whatever check
> is correct in that version.

Ok, you are right. raw was the only exception because it could be used
as a protocol even though it didn't have a protocol name.

Looks fine to me then if you enforce the limitation instead of only
printing an error message and opening the image anyway. Not printing the
error and opening the image would be fine either. I just don't like
error messages without errors.

Kevin