On 12/01/2018 12:42 AM, Willem de Bruijn wrote:
> On Fri, Nov 30, 2018 at 5:48 PM Song Liu <liu.song....@gmail.com> wrote:
>>
>> On Fri, Nov 30, 2018 at 12:09 PM Willem de Bruijn
>> <willemdebruijn.ker...@gmail.com> wrote:
>>>
>>> From: Petar Penkov <ppen...@google.com>
>>>
>>> The pkt_len field in qdisc_skb_cb stores the skb length as it will
>>> appear on the wire after segmentation. For byte accounting, this value
>>> is more accurate than skb->len. It is computed on entry to the TC
>>> layer, so only valid there.
>>>
>>> Allow read access to this field from BPF tc classifier and action
>>> programs. The implementation is analogous to tc_classid, aside from
>>> restricting to read access.
>>>
>>> Signed-off-by: Petar Penkov <ppen...@google.com>
>>> Signed-off-by: Vlad Dumitrescu <vla...@google.com>
>>> Signed-off-by: Willem de Bruijn <will...@google.com>
>>> ---
>>> include/uapi/linux/bpf.h | 1 +
>>> net/core/filter.c | 16 +++++++++++
>>> tools/include/uapi/linux/bpf.h | 1 +
>>> tools/testing/selftests/bpf/test_verifier.c | 32 +++++++++++++++++++++
>>> 4 files changed, 50 insertions(+)
>>
>> Please split this into 3 patches:
>> 1 for include/uapi/linux/bpf.h and filter.c
>> 1 for tools/include/uapi/linux/bpf.h
>> 1 for tools/testing/selftests/bpf/test_verifier.c
>>
>> Other than this
>> Acked-by: Song Liu <songliubrav...@fb.com>
>
> Thanks for the fast review.
>
> I'm happy to resend in three parts, of course, but am curious: what is
> the rationale for splitting this up?
>
> This patch follows the process for commit f11216b24219 ("bpf: add
> skb->tstamp r/w access from tc clsact and cg skb progs"), which went
> in as a single patch just last week.
Yeah, I think it's fine as is, one small thing I'm wondering though is
given that we now would have both 'skb->len' and 'skb->pkt_len', would
it be more intuitive for a BPF program developer to distinguish the two
by having the latter named e.g. 'skb->wire_len' so it's slightly more
obvious that it's including header size at post-segmentation? If not
probably some comment in the uapi header similar as in qdisc_pkt_len_init()
might be helpful in any case.
Thanks,
Daniel
