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Re: [Qemu-block] [Qemu-devel] [PATCH v6 08/15] qstring: Add qstring_wrap

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v6 08/15] qstring: Add qstring_wrap_str()
Date: Tue, 11 Oct 2016 10:05:42 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

On 10/11/2016 10:04 AM, Eric Blake wrote:
> On 10/11/2016 06:08 AM, Marc-André Lureau wrote:
>>> +++ b/block.c
>>> @@ -1640,7 +1640,8 @@ static BlockDriverState
>>> *bdrv_append_temp_snapshot(BlockDriverState *bs,
>>>      qdict_put(snapshot_options, "file.driver",
>>>                qstring_from_str("file"));
>>>      qdict_put(snapshot_options, "file.filename",
>>> -              qstring_from_str(tmp_filename));
>>> +              qstring_wrap_str(tmp_filename));
>>> +    tmp_filename = NULL;
>>>      qdict_put(snapshot_options, "driver",
>>>                qstring_from_str("qcow2"));
>> You could also remove g_free(tmp_filename) from the normal return path
>> (this may please static analyzers).
> No. g_free(NULL) is safe, but we can also reach the 'out' label with
> tmp_filename still malloc'd prior to the place where we transfer it
> here, so the g_free() in the cleanup label is still required.  The
> assignment to NULL here prevents a double free.  The patch is correct as-is.

Spoke too soon.  I see what you're saying - the normal return path now
has a dead g_free(NULL).  It won't cause any grief to the static
analyzers, but it is a useless no-op function call, so I can indeed trim
it (the one before the label, not the one after).

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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