Re: [PATCH v8 20/30] tap: Convert tap6_handler() to iov_tail

[Laurent Vivier <lvivier@redhat.com>]

On 06/08/2025 08:21, David Gibson wrote:
> On Tue, Aug 05, 2025 at 05:46:18PM +0200, Laurent Vivier wrote:
>> Use packet_data() and extract headers using IOV_REMOVE_HEADER()
>> and IOV_PEEK_HEADER() rather than packet_get().
>>
>> Remove packet_get() as it is not used anymore.
> 
> [snip]
>> @@ -896,21 +896,28 @@ resume:
>>   	for (seq_count = 0, seq = NULL; i < in->count; i++) {
>>   		size_t l4len, plen, check;
>>   		struct in6_addr *saddr, *daddr;
>> +		struct ipv6hdr ip6h_storage;
>> +		struct ethhdr eh_storage;
>> +		struct udphdr uh_storage;
>>   		const struct ethhdr *eh;
>>   		const struct udphdr *uh;
>>   		struct iov_tail data;
>>   		struct ipv6hdr *ip6h;
>>   		uint8_t proto;
>> -		char *l4h;
>>   
>> -		eh =   packet_get(in, i, 0,		sizeof(*eh), NULL);
>> +		if (!packet_data(in, i, &data))
>> +			return -1;
>> +
>> +		eh = IOV_REMOVE_HEADER(&data, eh_storage);
>>   		if (!eh)
>>   			continue;
>>   
>> -		ip6h = packet_get(in, i, sizeof(*eh),	sizeof(*ip6h), &check);
>> +		ip6h = IOV_PEEK_HEADER(&data, ip6h_storage);
>>   		if (!ip6h)
>>   			continue;
> 
> You peek the IPv6 header here, but I haven't spotted where you remove
> / drop it before...
> 

In fact, data offset is modified by ipv6_l4hdr() that scans the headers and the data 
provided to ipv6_l4hdr() must point to an ipv6hdr (it provides also the proto that is 
alloed to do the correct IOV_PEEK_HEADER()).

Thanks,
Laurent