[ovs-dev] [PATCH v12 2/3] dp-packet: Init specific mbuf fields.

[Ilya Maximets]

On 02.11.2018 12:06, Tiago Lam wrote:
> From: Mark Kavanagh <mark.b.kavanagh at intel.com>
> 
> dp_packets are created using xmalloc(); in the case of OvS-DPDK, it's
> possible the the resultant mbuf portion of the dp_packet contains
> random data. For some mbuf fields, specifically those related to
> multi-segment mbufs and/or offload features, random values may cause
> unexpected behaviour, should the dp_packet's contents be later copied
> to a DPDK mbuf. It is critical therefore, that these fields should be
> initialized to 0.
> 
> This patch ensures that the following mbuf fields are initialized to
> appropriate values on creation of a new dp_packet:
>    - ol_flags=0
>    - nb_segs=1
>    - tx_offload=0
>    - packet_type=0
>    - next=NULL

I don't understand why we need this, at least without multi-segs.
malloced packets never reaches dpdk library functions. We're always
re-allocating them. The only exception is the call to egress policer,
but we can clear some fields right before it inside dpdk_do_tx_copy().

We're only using ol_flags, but this field already cleared in current code.

In general, I'd like to drop these 'mbuf' related references in generic
code at all like it done in my recent patch-set:
	https://patchwork.ozlabs.org/patch/990181/

Best regards, Ilya Maximets.

> 
> Adapted from an idea by Michael Qiu <qiudayu at chinac.com>:
> https://patchwork.ozlabs.org/patch/777570/
> 
> Co-authored-by: Tiago Lam <tiago.lam at intel.com>
> 
> Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
> Signed-off-by: Tiago Lam <tiago.lam at intel.com>
> Acked-by: Eelco Chaudron <echaudro at redhat.com>
> Acked-by: Flavio Leitner <fbl at sysclose.org>
> ---
>  lib/dp-packet.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/dp-packet.h b/lib/dp-packet.h
> index 5b4c9c7..fe34d04 100644
> --- a/lib/dp-packet.h
> +++ b/lib/dp-packet.h
> @@ -498,14 +498,14 @@ dp_packet_mbuf_rss_flag_reset(struct dp_packet *p)
>      p->mbuf.ol_flags &= ~PKT_RX_RSS_HASH;
>  }
>  
> -/* This initialization is needed for packets that do not come
> - * from DPDK interfaces, when vswitchd is built with --with-dpdk.
> - * The DPDK rte library will still otherwise manage the mbuf.
> - * We only need to initialize the mbuf ol_flags. */
> +/* This initialization is needed for packets that do not come from DPDK
> + * interfaces, when vswitchd is built with --with-dpdk. */
>  static inline void
>  dp_packet_mbuf_init(struct dp_packet *p)
>  {
> -    p->mbuf.ol_flags = 0;
> +    p->mbuf.ol_flags = p->mbuf.tx_offload = p->mbuf.packet_type = 0;
> +    p->mbuf.nb_segs = 1;
> +    p->mbuf.next = NULL;
>  }
>  
>  static inline bool
>