Re: [RFC PATCH bpf-next v6 3/3] selftests/bpf: Handle forwarding of UDP CLOCK_TAI packets

[Abhishek Chauhan (ABC)]

On 5/6/2024 1:54 PM, Abhishek Chauhan (ABC) wrote:
> 
> 
> On 5/6/2024 1:50 PM, Abhishek Chauhan (ABC) wrote:
>>
>>
>> On 5/6/2024 12:04 PM, Willem de Bruijn wrote:
>>> Abhishek Chauhan wrote:
>>>> With changes in the design to forward CLOCK_TAI in the skbuff
>>>> framework,  existing selftest framework needs modification
>>>> to handle forwarding of UDP packets with CLOCK_TAI as clockid.
>>>>
>>>> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@xxxxxxxxx/
>>>> Signed-off-by: Abhishek Chauhan <quic_abchauha@xxxxxxxxxxx>
>>>> ---
>>>>  tools/include/uapi/linux/bpf.h                | 15 ++++---
>>>>  .../selftests/bpf/prog_tests/ctx_rewrite.c    | 10 +++--
>>>>  .../selftests/bpf/prog_tests/tc_redirect.c    |  3 --
>>>>  .../selftests/bpf/progs/test_tc_dtime.c       | 39 +++++++++----------
>>>>  4 files changed, 34 insertions(+), 33 deletions(-)
>>>>
>>>> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
>>>> index 90706a47f6ff..25ea393cf084 100644
>>>> --- a/tools/include/uapi/linux/bpf.h
>>>> +++ b/tools/include/uapi/linux/bpf.h
>>>> @@ -6207,12 +6207,17 @@ union {					\
>>>>  	__u64 :64;			\
>>>>  } __attribute__((aligned(8)))
>>>>  
>>>> +/* The enum used in skb->tstamp_type. It specifies the clock type
>>>> + * of the time stored in the skb->tstamp.
>>>> + */
>>>>  enum {
>>>> -	BPF_SKB_TSTAMP_UNSPEC,
>>>> -	BPF_SKB_TSTAMP_DELIVERY_MONO,	/* tstamp has mono delivery time */
>>>> -	/* For any BPF_SKB_TSTAMP_* that the bpf prog cannot handle,
>>>> -	 * the bpf prog should handle it like BPF_SKB_TSTAMP_UNSPEC
>>>> -	 * and try to deduce it by ingress, egress or skb->sk->sk_clockid.
>>>> +	BPF_SKB_TSTAMP_UNSPEC = 0,		/* DEPRECATED */
>>>> +	BPF_SKB_TSTAMP_DELIVERY_MONO = 1,	/* DEPRECATED */
>>>> +	BPF_SKB_CLOCK_REALTIME = 0,
>>>> +	BPF_SKB_CLOCK_MONOTONIC = 1,
>>>> +	BPF_SKB_CLOCK_TAI = 2,
>>>> +	/* For any future BPF_SKB_CLOCK_* that the bpf prog cannot handle,
>>>> +	 * the bpf prog can try to deduce it by ingress/egress/skb->sk->sk_clockid.
>>>>  	 */
>>>>  };
>>>>  
>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
>>>> index 3b7c57fe55a5..71940f4ef0fb 100644
>>>> --- a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
>>>> +++ b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
>>>> @@ -69,15 +69,17 @@ static struct test_case test_cases[] = {
>>>>  	{
>>>>  		N(SCHED_CLS, struct __sk_buff, tstamp),
>>>>  		.read  = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
>>>> -			 "w11 &= 3;"
>>>> -			 "if w11 != 0x3 goto pc+2;"
>>>> +			 "if w11 == 0x4 goto pc+1;"
>>>> +			 "goto pc+4;"
>>>> +			 "if w11 == 0x3 goto pc+1;"
>>>> +			 "goto pc+2;"
>>>
>>> Not an expert on this code, and I see that the existing code already
>>> has this below, but: isn't it odd and unnecessary to jump to an
>>> unconditional jump statement?
>>>
>> I am closely looking into your comment and i will evalute it(Martin can correct me 
>> if the jumps are correct or not as i am new to BPF as well) but i found out that 
>> JSET = "&" and not "==". So the above two ins has to change from -   
>>
>> "if w11 == 0x4 goto pc+1;" ==>(needs to be corrected to) "if w11 & 0x4 goto pc+1;" 
>>  "if w11 == 0x3 goto pc+1;" ==> (needs to be correct to) "if w11 & 0x3 goto pc+1;"
>>
>>
Willem, I looked at the jumps in the above code. They look correct to me. 
Martin can check too if i am doing anything wrong here other than the JSET "&".

Ideally pc(program counter) points to the next instruction. 

			 "if w11 & 0x4 goto pc+1;"
			 "goto pc+4;" 
		[pc+0]	 "if w11 & 0x3 goto pc+1;" <== PC is going to be here 
		[pc+1]	 "goto pc+2;"
		[pc+2]	 "$dst = 0;"
		[pc+3]	 "goto pc+1;"
		[pc+4]	 "$dst = *(u64 *)($ctx + sk_buff::tstamp);", <== This is where the code is intended to jump to for "goto pc+4;"



>>>>  			 "$dst = 0;"
>>>>  			 "goto pc+1;"
>>>>  			 "$dst = *(u64 *)($ctx + sk_buff::tstamp);",
>>>>  		.write = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
>>>> -			 "if w11 & 0x2 goto pc+1;"
>>>> +			 "if w11 & 0x4 goto pc+1;"
>>>>  			 "goto pc+2;"
>>>> -			 "w11 &= -2;"
>>>> +			 "w11 &= -3;"