Re: [PATCH V3 1/2] block/nbd: extract the common cleanup code

[pannengyuan]

On 2019/12/4 3:00, Eric Blake wrote:
> On 11/29/19 1:25 AM, address@hidden wrote:
>> From: PanNengyuan <address@hidden>
>>
>> The BDRVNBDState cleanup code is common in two places, add
>> nbd_free_bdrvstate_prop() function to do these cleanups (suggested by
>> Stefano Garzarella).
>>
>> Signed-off-by: PanNengyuan <address@hidden>
>> ---
>>   block/nbd.c | 23 +++++++++++++----------
>>   1 file changed, 13 insertions(+), 10 deletions(-)
>>
>> diff --git a/block/nbd.c b/block/nbd.c
>> index 1239761..5805979 100644
>> --- a/block/nbd.c
>> +++ b/block/nbd.c
>> @@ -94,6 +94,8 @@ typedef struct BDRVNBDState {
>>     static int nbd_client_connect(BlockDriverState *bs, Error **errp);
>>   +static void nbd_free_bdrvstate_prop(BDRVNBDState *s);
>> +
> 
> Why do you need a static function prototype?  Just implement the
> function prior to its first use, then you won't need a forward declaration.

Yes, It's not necessary. I will change it.

> 
>>   static void nbd_channel_error(BDRVNBDState *s, int ret)
>>   {
>>       if (ret == -EIO) {
>> @@ -1486,6 +1488,15 @@ static int nbd_client_connect(BlockDriverState
>> *bs, Error **errp)
>>       }
>>   }
>>   +static void nbd_free_bdrvstate_prop(BDRVNBDState *s)
>> +{
>> +    object_unref(OBJECT(s->tlscreds));
>> +    qapi_free_SocketAddress(s->saddr);
>> +    g_free(s->export);
>> +    g_free(s->tlscredsid);
>> +    g_free(s->x_dirty_bitmap);
>> +}
> 
> In fact, it appears that you did just that, as the first use...
> 
> Bike-shedding: the name 'nbd_free_bdrvstate_prop' doesn't seem right to
> me - when I see a function with 'free' in the name taking a single
> pointer, I assume that the given pointer (here, BDRVNBDState *s) is
> freed - but your function does NOT free then incoming pointer.  Rather,
> you are clearing out the contents within a pre-allocated object which
> remains allocated.  What's more, since the object remains allocated, I'm
> surprised that you are not setting fields to NULL to prevent
> use-after-free bugs.
> 
> Either this function should also free s (in which case naming it merely
> 'nbd_free_bdrvstate' might be better), or you should consider naming it
> 'nbd_clear_bdrvstate' and assigning cleared fields to NULL.
> 

thanks, 'nbd_clear_bdrvstate' seems nice. I will replace the name and
set fields to NULL in next version.

>> +
>>   /*
>>    * Parse nbd_open options
>>    */
>> @@ -1855,10 +1866,7 @@ static int nbd_process_options(BlockDriverState
>> *bs, QDict *options,
>>      error:
>>       if (ret < 0) {
>> -        object_unref(OBJECT(s->tlscreds));
>> -        qapi_free_SocketAddress(s->saddr);
>> -        g_free(s->export);
>> -        g_free(s->tlscredsid);
>> +        nbd_free_bdrvstate_prop(s);
> 
> ...is here.
> 
>>       }
>>       qemu_opts_del(opts);
>>       return ret;
>> @@ -1937,12 +1945,7 @@ static void nbd_close(BlockDriverState *bs)
>>       BDRVNBDState *s = bs->opaque;
>>         nbd_client_close(bs);
>> -
>> -    object_unref(OBJECT(s->tlscreds));
>> -    qapi_free_SocketAddress(s->saddr);
>> -    g_free(s->export);
>> -    g_free(s->tlscredsid);
>> -    g_free(s->x_dirty_bitmap);
>> +    nbd_free_bdrvstate_prop(s);
>>   }
>>     static int64_t nbd_getlength(BlockDriverState *bs)
>>
>