Re: [PATCH v5 4/5] tcp: Update TCP checksum using an iovec array

[Stefano Brivio <sbrivio@redhat.com>]

On 2 October 2024 09:39:23 CEST, Laurent Vivier <lvivier@redhat.com> wrote:
>On 01/10/2024 20:22, Stefano Brivio wrote:
>> On Tue, 1 Oct 2024 09:29:28 +0200
>> Stefano Brivio <sbrivio@redhat.com> wrote:
>> 
>>> On Fri, 27 Sep 2024 15:53:48 +0200
>>> Laurent Vivier <lvivier@redhat.com> wrote:
>>> 
>>>> [...]
>>>> 
>>>> +void tcp_update_check_tcp4(const struct iphdr *iph,
>>>> +			   const struct iovec *iov, int iov_cnt,
>>>> +			   size_t l4offset)
>>>>   {
>>>>   	uint16_t l4len = ntohs(iph->tot_len) - sizeof(struct iphdr);
>>>>   	struct in_addr saddr = { .s_addr = iph->saddr };
>>>>   	struct in_addr daddr = { .s_addr = iph->daddr };
>>>> -	uint32_t sum = proto_ipv4_header_psum(l4len, IPPROTO_TCP, saddr, daddr);
>>>> +	size_t check_ofs;
>>>> +	__sum16 *check;
>>>> +	int check_idx;
>>>> +	uint32_t sum;
>>>> +	uintptr_t ptr;
>>>> +
>>>> +	sum = proto_ipv4_header_psum(l4len, IPPROTO_TCP, saddr, daddr);
>>>> +
>>>> +	check_idx = iov_skip_bytes(iov, iov_cnt,
>>>> +				   l4offset + offsetof(struct tcphdr, check),
>>>> +				   &check_ofs);
>>>> +
>>>> +	if (check_idx >= iov_cnt) {
>>>> +		err("TCP4 buffer is too small, iov size %zd, check offset %zd",
>>>> +		    iov_size(iov, iov_cnt),
>>>> +		    l4offset + offsetof(struct tcphdr, check));
>>>> +		return;
>>>> +	}
>>>>   -	bp->th.check = 0;
>>>> -	bp->th.check = csum(bp, l4len, sum);
>>>> +	if (check_ofs + sizeof(*check) > iov[check_idx].iov_len) {
>>>> +		err("TCP4 checksum field memory is not contiguous "
>>>> +		    "check_ofs %zd check_idx %d iov_len %zd",
>>>> +		    check_ofs, check_idx, iov[check_idx].iov_len);
>>>> +		return;
>>>> +	}
>>>> +
>>>> +	ptr = (uintptr_t)((char *)iov[check_idx].iov_base + check_ofs);
>>>> +	if (ptr & (__alignof__(*check) - 1)) {
>>>> +		err("TCP4 checksum field is not correctly aligned in memory");
>>>> +		return;
>>>> +	}
>>>> +
>>>> +	check = (__sum16 *)ptr;
>>> 
>>> clang-tidy (14.0.6) says:
>>> 
>>> /home/sbrivio/passt/tcp.c:803:10: error: integer to pointer cast pessimizes optimization opportunities [performance-no-int-to-ptr,-warnings-as-errors]
>>>          check = (__sum16 *)ptr;
>>>                  ^
>>> /home/sbrivio/passt/tcp.c:854:10: error: integer to pointer cast pessimizes optimization opportunities [performance-no-int-to-ptr,-warnings-as-errors]
>>>          check = (__sum16 *)ptr;
>>>                  ^
>>> 
>>> ...I'm still trying to figure out what that actually means. If it's
>>> trivial I can fix that up on merge.
>> 
>> Something like this?
>
>It's ok for me. Do you want I resend a version with it or can you update the patch on the merge?

No no, thanks, I'll update this on merge.

-- 
Stefano