[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-block] [Qemu-devel] [PATCH for-2.11 3/5] block: Guard against
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH for-2.11 3/5] block: Guard against NULL bs->drv |
Date: |
Tue, 14 Nov 2017 16:36:32 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 |
On 2017-11-10 22:46, Eric Blake wrote:
> On 11/10/2017 02:31 PM, Max Reitz wrote:
>> We currently do not guard everywhere against a NULL bs->drv where we
>> should be doing so. Most of the places fixed here just do not care
>> about that case at all.
>>
>> Some care implicitly, e.g. through a prior function call to
>> bdrv_getlength() which would always fail for an ejected BDS. Add an
>> assert there to make it more obvious.
>>
>> Other places seem to care, but do so insufficiently: Freeing clusters in
>> a qcow2 image is an error-free operation, but it may leave the image in
>> an unusable state anyway. Giving qcow2_free_clusters() an error code is
>> not really viable, it is much easier to note that bs->drv may be NULL
>> even after a successful driver call. This concerns bdrv_co_flush(), and
>> the way the check is added to bdrv_co_pdiscard() (in every iteration
>> instead of only once).
>>
>> Finally, some places employ at least an assert(bs->drv); somewhere, that
>> may be reasonable (such as in the reopen code), but in
>> bdrv_has_zero_init(), it is definitely not. Returning 0 there in case
>> of an ejected BDS saves us much headache instead.
>>
>> Reported-by: R. Nageswara Sastry <address@hidden>
>> Buglink: https://bugs.launchpad.net/qemu/+bug/1728660
>> Signed-off-by: Max Reitz <address@hidden>
>> ---
>
>> +++ b/block/replication.c
>
>>
>> + if (!s->hidden_disk->bs->drv) {
>> + error_setg(errp, "Hidden disk %s is ejected",
>> + s->hidden_disk->bs->node_name);
>> + return;
>> + }
>
> How would the hidden disk ever be ejected? Could this be an assert instead?
Maybe? :-)
Isn't the hidden disk usually a qcow2 file? As such I guess there can
be corruptions in it that make the qcow2 driver eject it (even though
qemu isn't writing to it).
Max
> But what you have is equally safe, so
> Reviewed-by: Eric Blake <address@hidden>
signature.asc
Description: OpenPGP digital signature
[Qemu-block] [PATCH for-2.11 5/5] qcow2: Refuse to get unaligned offsets from cache, Max Reitz, 2017/11/10