On Fri, Jun 17, 2016 at 6:15 PM, Daniel Borkmann <dan...@iogearbox.net> wrote:
> On 06/17/2016 04:43 PM, Saeed Mahameed wrote:
>>
>> From: Maor Gottlieb <ma...@mellanox.com>
>>
>> Add new packet type to skip kernel specific protocol handlers.
>>
>> This is needed so device drivers can pass packets up to user space
>> (af_packet/tcpdump, etc..) without the need for them to go through
>> the whole kernel data path.
>>
>> Signed-off-by: Maor Gottlieb <ma...@mellanox.com>
>> CC: David S. Miller <da...@davemloft.net>
>> CC: Patrick McHardy <ka...@trash.net>
>> CC: Eric Dumazet <eduma...@google.com>
>> Signed-off-by: Saeed Mahameed <sae...@mellanox.com>
>> ---
>> include/linux/skbuff.h | 6 +++---
>> include/uapi/linux/if_packet.h | 1 +
>> net/core/dev.c | 4 ++++
>> 3 files changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index dc0fca7..359724e 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -694,14 +694,14 @@ struct sk_buff {
>>
>> /* if you move pkt_type around you also must adapt those constants */
>> #ifdef __BIG_ENDIAN_BITFIELD
>> -#define PKT_TYPE_MAX (7 << 5)
>> +#define PKT_TYPE_MAX (8 << 5)
>> #else
>> -#define PKT_TYPE_MAX 7
>> +#define PKT_TYPE_MAX 8
>> #endif
>
>
> Aehm ... did you actually test this with BPF ?!
>
> PKT_TYPE_MAX is a mask (naming could be better no doubt), see also function
> convert_skb_access():
>
> [...]
> case SKF_AD_PKTTYPE:
> *insn++ = BPF_LDX_MEM(BPF_B, dst_reg, src_reg,
> PKT_TYPE_OFFSET());
> *insn++ = BPF_ALU32_IMM(BPF_AND, dst_reg, PKT_TYPE_MAX);
> #ifdef __BIG_ENDIAN_BITFIELD
> *insn++ = BPF_ALU32_IMM(BPF_RSH, dst_reg, 5);
> #endif
> break;
> [...]
>
> Also, dunno if it's worth burning a skb bit for one driver.
>
oops! it didn't occur to me that it was used as a mask!
does this mean we are out of PKT_TYPE flags ?
Maybe we can use skb->mark instead ? any ideas ?
Also i am not sure it is a one driver thing, i know about other
examples where some device drivers set skb->protocol to 0xffff to
achieve the same ! which i didn't like.
