Re: [Qemu-devel] About the snapshot

[Zhi Hui Li <zhihuili@linux.vnet.ibm.com>]

On 2011年12月06日 17:40, Stefan Hajnoczi wrote:
> On Tue, Dec 6, 2011 at 9:07 AM, Zhi Hui Li<zhihuili@linux.vnet.ibm.com>  wrote:
>>
>> 1) :
>>
>> for example:
>>
>> BDRVQcowState *s = bs->opaque;
>>
>> s->snapshots
>> s->nb_snapshots
>>
>>
>> 1:use the command:   qemu-img snapshot ./test.qcow2  -c aa
>> the memory of the s->snapshot don't free,
>> if the s->nb_snapshots is large, Does it have some problems.
>>
>> 2: use the command:  qemu-system-x86_64  ./test.qcow2 -snapshot
>> when the program ends, Does it need to free the s->snapshots ?
>
> These two commands are unrelated.  QEMU uses the term "snapshot" for
> several different features:
>
> 1. qemu-img snapshot refers to "internal snapshots" that are contained
> within qcow2 image files.  The savevm/loadvm/delvm monitor commands
> operate on internal snapshots.
>
> 2. qemu -snapshot refers to a temporary qcow2 image file created to
> buffer any data that the guest writes.  When QEMU exits your disk
> image is not modified and the temporary qcow2 file is deleted.  You
> can also apply the buffer to the disk image using the "commit" monitor
> command.

yes, I understand what you say, but the qemu-img and savevm both call 
the function of qcow2_snapshot_create, when I use the command qemu-img 
snapshot ./test.qcow2  -c aa,
but the memory of the s->snapshot don't free.

>
>> 2):
>> in the function of
>> qcow2_update_snapshot_refcount
>>
>> it has some "  goto fail  ";
>> if the function runs some times, then something makes it goto fail,
>> I am not sure whether it will make the refcount  incorrect.
>
> When an error occurs its possible that refcount leaks are introduced
> (the refcount was increment but will never be used), but we should
> never decrement a reference that is still in use.
>
> Please be more specific about the problem so that Kevin or I can take a look.
>
> Stefan
>
Ok, I got it.

thank you very much !