Re: [PATCH v3] mbuf: decrease refcnt when detaching

[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