[ovs-dev] [PATCH v8 07/13] dp-packet: Handle multi-seg mbufs in put_uninit().

Eelco Chaudron echaudro at redhat.com
Tue Jun 26 10:35:26 UTC 2018



On 22 Jun 2018, at 21:04, Lam, Tiago wrote:

> On 18/06/2018 12:52, Eelco Chaudron wrote:
>>
>>
>> On 11 Jun 2018, at 18:21, Tiago Lam wrote:
>>
>>> The dp_packet_put_uninit() function is, in its current 
>>> implementation,
>>> operating on the data buffer of a dp_packet as if it were 
>>> contiguous,
>>> which in the case of multi-segment mbufs means they operate on the
>>> first
>>> mbuf in the chain. However, when making use of multi-segment mbufs, 
>>> it
>>> is the data length of the last mbuf in the mbuf chain that should be
>>> adjusted. This function has thus been modified to support
>>> multi-segment
>>> mbufs.
>>>
>>> Co-authored-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
>>>
>>> Signed-off-by: Mark Kavanagh <mark.b.kavanagh at intel.com>
>>> Signed-off-by: Tiago Lam <tiago.lam at intel.com>
>>> ---
>>>  lib/dp-packet.c | 12 ++++++++++++
>>>  1 file changed, 12 insertions(+)
>>>
>>> diff --git a/lib/dp-packet.c b/lib/dp-packet.c
>>> index 2aaeaae..9f8503e 100644
>>> --- a/lib/dp-packet.c
>>> +++ b/lib/dp-packet.c
>>> @@ -321,7 +321,19 @@ dp_packet_put_uninit(struct dp_packet *b, 
>>> size_t
>>> size)
>>>      void *p;
>>>      dp_packet_prealloc_tailroom(b, size);
>>>      p = dp_packet_tail(b);
>>> +#ifdef DPDK_NETDEV
>>> +    struct rte_mbuf *mbuf;
>>> +
>>> +    if (b->source == DPBUF_DPDK) {
>>> +        mbuf = rte_pktmbuf_lastseg(&b->mbuf);
>>> +    } else {
>>> +        mbuf = CONST_CAST(struct rte_mbuf *, &b->mbuf);
>>> +    }
>>> +
>>> +    mbuf->data_len += size;
>>
>> How can we be sure there is room in the (last) mbuf->data? The
>> dp_packet_set_size() is not allocating more room (but it's 
>> truncating).
>
> dp_packet_prealloc_tailroom() called at the top is responsible for
> arranging memory and make sure it returns with enough memory. 
> Otherwise,
> it keeps the same behavior of hard asserting.

Yes I feel it’s a bad design in the first place to assert() if there 
is not enough memory to handle a packet. But nothing your patch can do 
about this, Ack.

>> The mbuf->data_len should be handled in dp_packet_set_size(), and not
>> here so it will work for all these cases.
>>
> This was a leftover, thanks for spotting it! I've fixed it and will
> include with the next iteration.
>
> Tiago.


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