Re: [Qemu-devel] [PATCH] block: reject O_RDWR open for read-only images

[Kevin Wolf <kwolf@redhat.com>]

Am 07.04.2010 13:57, schrieb Christoph Hellwig:
> Various obscure image format drivers do not allow write access.
> Instead of silently falling back to read-only access reject attempts
> to open these images for write access.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

I'm not sure about this patch. I don't have any such images around, so I
can't test it easily, but it looks to me as if you'd need to explicitly
specify readonly=on if you want to use such formats. This in turn means
that old style shortcuts like -hda don't work any more. Is it that
important to avoid implicit fallbacks for obscure formats that we're
willing to sacrifice compatibility?

That said, personally I don't care about those format all that much
anyway and the change would make things more consistent. If people
consider it okay to break compatibility in this way, I won't stand in
your way.

But if we wanted to implement this, have you thought about doing it in
one place in block.c? You could check if a driver supports bdrv_write or
bdrv_aio_write, and if it doesn't support either I think you can assume
it's read-only.

Kevin