Re: [dpdk-dev] [PATCH v3] mbuf: decrease refcnt when detaching

[Hiroyuki Mikita <h.mikita89@gmail.com>]

Hi Olivier,

Thanks for reviewing.

I am fixing the patch to follow your comments.

Regards,
Hiroyuki

2016-05-18 20:58 GMT+09:00 Olivier Matz <olivier.matz@6wind.com>:
> Hi Hiroyuki,
>
> Thanks for submitting a new version.
>
> There are some styling issues in the patch, I highlighted them below
> but you can check them by using checkpatch:
>
>   DPDK_CHECKPATCH_PATH=/path/to/linux/checkpatch.pl \
>     scripts/checkpatches.sh file.patch
>
>
> On 05/17/2016 06:35 PM, Hiroyuki Mikita wrote:
>> The rte_pktmbuf_detach() function should decrease refcnt on a direct
>> buffer.
>>
>> Signed-off-by: Hiroyuki Mikita <h.mikita89@gmail.com>
>>
>> [...]
>>
>> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
>> index 529debb..299b60e 100644
>> --- a/lib/librte_mbuf/rte_mbuf.h
>> +++ b/lib/librte_mbuf/rte_mbuf.h
>> @@ -1408,6 +1408,8 @@ static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool,
>>   *
>>   * After attachment we refer the mbuf we attached as 'indirect',
>>   * while mbuf we attached to as 'direct'.
>> + * The direct mbuf's reference counter is incremented.
>> + *
>
> ERROR:TRAILING_WHITESPACE: trailing whitespace
> #82: FILE: lib/librte_mbuf/rte_mbuf.h:1412:
> + * $
>
>
>>   * Right now, not supported:
>>   *  - attachment for already indirect mbuf (e.g. - mi has to be direct).
>>   *  - mbuf we trying to attach (mi) is used by someone else
>> @@ -1462,12 +1464,15 @@ static inline void rte_pktmbuf_attach(struct rte_mbuf *mi, struct rte_mbuf *m)
>>   *  - restore original mbuf address and length values.
>>   *  - reset pktmbuf data and data_len to their default values.
>>   *  All other fields of the given packet mbuf will be left intact.
>> + *  - decrement the direct mbuf's reference counter.
>> + *  When the reference counter becomes 0, the direct mbuf is freed.
>
> Minor comment here: I think something like that would be clearer:
>
>   *  - restore original mbuf address and length values.
>   *  - reset pktmbuf data and data_len to their default values.
>   *  - decrement the direct mbuf's reference counter. When the
>   *    reference counter becomes 0, the direct mbuf is freed.
>   *
>   * All other fields of the given packet mbuf will be left intact.
>
>
>>   *
>>   * @param m
>>   *   The indirect attached packet mbuf.
>>   */
>>  static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
>>  {
>> +     struct rte_mbuf *md = rte_mbuf_from_indirect(m);
>>       struct rte_mempool *mp = m->pool;
>>       uint32_t mbuf_size, buf_len, priv_size;
>>
>> @@ -1482,6 +1487,10 @@ static inline void rte_pktmbuf_detach(struct rte_mbuf *m)
>>       m->data_off = RTE_MIN(RTE_PKTMBUF_HEADROOM, (uint16_t)m->buf_len);
>>       m->data_len = 0;
>>       m->ol_flags = 0;
>> +
>> +     if (rte_mbuf_refcnt_update(md, -1) == 0) {
>> +             __rte_mbuf_raw_free(md);
>> +     }
>>  }
>
> WARNING:BRACES: braces {} are not necessary for single statement blocks
> #107: FILE: lib/librte_mbuf/rte_mbuf.h:1491:
> +       if (rte_mbuf_refcnt_update(md, -1) == 0) {
> +               __rte_mbuf_raw_free(md);
> +       }
>
>
>>
>>  static inline struct rte_mbuf* __attribute__((always_inline))
>> @@ -1491,15 +1500,9 @@ __rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>>
>>       if (likely(rte_mbuf_refcnt_update(m, -1) == 0)) {
>>
>> -             /* if this is an indirect mbuf, then
>> -              *  - detach mbuf
>> -              *  - free attached mbuf segment
>> -              */
>> +             /* if this is an indirect mbuf, it is detached. */
>>               if (RTE_MBUF_INDIRECT(m)) {
>> -                     struct rte_mbuf *md = rte_mbuf_from_indirect(m);
>>                       rte_pktmbuf_detach(m);
>> -                     if (rte_mbuf_refcnt_update(md, -1) == 0)
>> -                             __rte_mbuf_raw_free(md);
>>               }
>>               return m;
>>       }
>>
>
> It's not seen by checkpatch, but the braces could also be removed
> here.
>
> Apart from this, it looks good to me. I'm ok with not providing a
> compat function as we could consider it was a bug.
>
> Thanks for working on this.
>
> Olivier
>