[Qemu-devel] Re: [PATCH] block: Enable fall-back to read-only for backing file

[Kevin Wolf <kwolf@redhat.com>]

Am 31.01.2010 17:49, schrieb Naphtali Sprei:
> There's a problem when trying to use an image file based on a read-only image file.
> Before this patch, qemu fails to open the base image and stop.
> With this patch, qemu tries to open the backing file with same permissions as the "top" file,
> but if it fails, qemu tries to open it with read-only permissions. If succeeded it goes on.
> 
> This fall-back works both for an image file based on a read-only file
> and also for a read-only file opened with the snapshot attribute/mode (where the real file is the backing file
> for the snapshot file).
> 
> Is it better to always open the backing file with read-only mode ? this will be more consistent/predictable ?

I would love to open them read-only unconditionally, but we can't. It
would break the commit monitor command. I think the read-only fallback
is appropriate for backing files.

Kevin