Re: [PATCH 1/4] rte_mbuf: add rte_pktmbuf_coalesce

[Olivier Matz <olivier.matz@6wind.com>]

Hi Tomasz,

On Fri,  2 Dec 2016 18:07:43 +0100, Tomasz Kulasek
<tomaszx.kulasek@intel.com> wrote:
> This patch adds function rte_pktmbuf_coalesce to let crypto PMD
> coalesce chained mbuf before crypto operation and extend their
> capabilities to support segmented mbufs when device cannot handle
> them natively.
> 
> 
> Signed-off-by: Tomasz Kulasek <tomaszx.kulasek@intel.com>
> ---
>  lib/librte_mbuf/rte_mbuf.h |   34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index ead7c6e..f048681 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -1647,6 +1647,40 @@ static inline int rte_pktmbuf_chain(struct
> rte_mbuf *head, struct rte_mbuf *tail }
>  
>  /**
> + * Coalesce data from mbuf to the continuous buffer.
> + *
> + * @param mbuf_dst
> + *   Contiguous destination mbuf
> + * @param mbuf_src
> + *   Uncontiguous source mbuf
> + *
> + * @return
> + *   - 0, on success
> + *   - -EINVAL, on error
> + */

I think the API should be clarified. In your case, it is expected that the
destination mbuf is already filled with uninitialized data (i.e. that
rte_pktmbuf_append() has been called).

We could wonder if a better API wouldn't be to allocate the dst mbuf in
the function, call append()/prepend(), and do the copy.

Even better, we could have:

  int rte_pktmbuf_linearize(struct rte_mbuf *m)

It will reuse the same mbuf (maybe moving the data).


> +
> +#include <rte_hexdump.h>

This should be removed.

> +
> +static inline int
> +rte_pktmbuf_coalesce(struct rte_mbuf *mbuf_dst, struct rte_mbuf *mbuf_src) {

Source mbuf should be const.

> +	char *dst;
> +
> +	if (!rte_pktmbuf_is_contiguous(mbuf_dst) ||
> +			rte_pktmbuf_data_len(mbuf_dst) >=
> +			rte_pktmbuf_pkt_len(mbuf_src))
> +		return -EINVAL;

Why >= ?

> +
> +	dst = rte_pktmbuf_mtod(mbuf_dst, char *);
> +
> +	if (!__rte_pktmbuf_read(mbuf_src, 0, rte_pktmbuf_pkt_len(mbuf_src),
> +			dst))

When a function returns a pointer, I think it is clearer to do:
  if (func() == NULL)
than:
  if (!func())


> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +/**
>   * Dump an mbuf structure to a file.
>   *
>   * Dump all fields for the given packet mbuf and all its associated


One more question, I don't see where this function is used in your
patchset. What is your use-case?

Regards,
Olivier