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From: Olivier MATZ <olivier.matz@6wind.com>
To: Zoltan Kiss <zoltan.kiss@linaro.org>, dev@dpdk.org,  dev@openvswitch.org
Subject: Re: [dpdk-dev] ovs-dpdk: placing the metadata
Date: Wed, 25 Mar 2015 18:04:07 +0100
Message-ID: <5512EA87.1020707@6wind.com> (raw)
In-Reply-To: <5511A1F0.40605@linaro.org>

Hi Zoltan,

On 03/24/2015 06:42 PM, Zoltan Kiss wrote:
> Hi,
>
> I've noticed in lib/netdev-dpdk.c that __rte_pktmbuf_init() stores the
> packet metadata right after "struct rte_mbuf", and before the buffer data:
>
>      /* start of buffer is just after mbuf structure */
>      m->buf_addr = (char *)m + sizeof(struct dp_packet);
>
> (struct dp_packet has the rte_mbuf as first member if DPDK enabled)
>
> However, lib/librte_mbuf/rte_mbuf.h seems to codify that the buffer
> should start right after the rte_mbuf:
>
> /**
>   * Given the buf_addr returns the pointer to corresponding mbuf.
>   */
> #define RTE_MBUF_FROM_BADDR(ba)     (((struct rte_mbuf *)(ba)) - 1)
>
> /**
>   * Given the pointer to mbuf returns an address where it's  buf_addr
>   * should point to.
>   */
> #define RTE_MBUF_TO_BADDR(mb)       (((struct rte_mbuf *)(mb)) + 1)
>
> These macros are used for attaching/detaching mbuf's to each other. This
> is the way the code retrieves the direct buffer from an indirect one,
> and vica versa. I think if we want to keep the metadata feature (which I
> guess is quite important), we need to add a pointer to rte_mbuf, which
> helps the direct and indirect structs to find each other. Something like:
>
>      struct rte_mbuf *attach;    /**< Points to the other buffer if this
> one
>                       is (in)direct. Otherwise NULL.  */
>
> What do you think?

I've just sent a patch that should fix this issue.
http://dpdk.org/ml/archives/dev/2015-March/015722.html

Let me know if you have any comment on it.

Regards,
Olivier

  reply	other threads:[~2015-03-25 17:04 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-24 17:42 Zoltan Kiss
2015-03-25 17:04 ` Olivier MATZ [this message]
2015-03-25 18:57   ` Zoltan Kiss
2015-03-26  8:44     ` Olivier MATZ

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