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Date: Mon, 06 Jun 2011 12:00:00 +0200
From: Kevin Wolf <kwolf@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] bdrv_img_create: Fix segfault
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel@nongnu.org

Am 02.06.2011 00:34, schrieb Stefan Hajnoczi:
> On Wed, Jun 1, 2011 at 1:05 PM, Kevin Wolf <kwolf@redhat.com> wrote:
>> Block drivers that don't support creating images don't have a size option. Fail
>> gracefully instead of segfaulting when trying to access the option's value.
>>
>> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> ---
>>  block.c |    5 +++--
>>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> A command-line to reproduce the crash would be nice.

qemu-img create -f bochs nbd:foo 32M

It doesn't happen with a file protocol any more since we merge the
create options of the protocol with those of the format (was introduced
with Sheepdog).

> I noticed this line above your fix:
> set_option_parameter_int(param, BLOCK_OPT_SIZE, img_size);
> 
> If I follow correctly there should be an "Unknown option 'size'" error
> message before set_option_parameter_int() returns -1 (which we ignore)
> and then crash.

Right, this is what happens.

> Perhaps we should just catch the error when set_option_parameter_int() fails?

We could do that, but the segfault isn't really related to a failing
set_option_parameter_int() but to the failing get_option_parameter(). I
think it's good style not to rely on the error handling of an unrelated
action some lines above.

Adding some error handling there, too, wouldn't hurt, though.

Kevin