On Tue, Mar 7, 2023 at 3:14 PM HAGIO KAZUHITO(萩尾 一仁) <k-hagio-ab@xxxxxxx> wrote:
On 2023/03/07 13:46, lijiang wrote:
>> > + char str[INET6_ADDRSTRLEN + 1] = {0};
>> > + char buffer[INET6_ADDRSTRLEN + 4] = {0};
>>
>> What are the +1 and +4 for?
>>
>>
>> I noticed that the size of INET6_ADDRSTRLEN is 48 in kernel code as below:
>>
>> --- a/include/linux/inet.h
>> +++ b/include/linux/inet.h
>> +/*
>> + * These mimic similar macros defined in user-space for inet_ntop(3).
>> + * See /usr/include/netinet/in.h .
>> + */
>> +#define INET_ADDRSTRLEN (16)
>> +#define INET6_ADDRSTRLEN (48)
>>
>>
>> And, the size of INET6_ADDRSTRLEN is 46 in my machine as below:
>>
>> # cat /usr/include/netinet/in.h |grep INET6_ADDRSTRLEN
>> #define INET6_ADDRSTRLEN 46
I'm not sure why the kernel one is 48 (for a multiple of 8?), but
the INET6_ADDRSTRLEN in glibc header should mean the longest result
of inet_ntop() in glibc, and the latest glibc also has the same 46.
So I don't think we need to consider the kernel one.
>>
>>
>> The rfc2460 said that the IPv6 increases the IP address size from 32 bits to 128 bits.
>>
>> crash> struct in6_addr
>> struct in6_addr {
>> union {
>> __u8 u6_addr8[16];
>> __be16 u6_addr16[8];
>> __be32 u6_addr32[4];
>> } in6_u;
>> }
>> SIZE: 16
>>
>> Given that, maybe they should be defined like this?
>>
>> + char str[INET6_ADDRSTRLEN + 2] = {0};
>> + char buffer[INET6_ADDRSTRLEN + 2 + 2] = {0};
>>
>> Not sure what's the best way for this case.
>>
>> Looking at the example in the man page of inet_pton(3), INET6_ADDRSTRLEN
>> seems enough for the str and contains a null char. The buffer can have
>> a comma and a space (", ") so +2 is enough? i.e.
>>
>> char str[INET6_ADDRSTRLEN] = {0};
>> char buffer[INET6_ADDRSTRLEN + 2] = {0};
>>
>>
>> > + uint len = 0;
>> > +
>> > + buf = *bufp;
>> > + pos = strlen(buf);
>>
>> Ah nicely done :)
>>
>> > +
>> > + readmem(devaddr + OFFSET(net_device_ip6_ptr), KVADDR,
>> > + &ip6_ptr, sizeof(ulong), "ip6_ptr", FAULT_ON_ERROR);
>> > +
>> > + if (!ip6_ptr)
>> > + return;
>> > +
>> > + if (VALID_MEMBER(inet6_ifaddr_if_list)) {
>> > + struct list_data list_data, *ld;
>> > + ulong cnt = 0, i;
>> > +
>> > + ld = &list_data;
>> > + BZERO(ld, sizeof(struct list_data));
>> > + ld->flags |= LIST_ALLOCATE;
>> > + ld->start = ip6_ptr + OFFSET(inet6_dev_addr_list);
>> > + cnt = do_list(ld);
>> > +
>> > + for (i = 1; i < cnt; i++) {
>> > +
>> > + addr = ld->list_ptr[i] + OFFSET(inet6_ifaddr_addr);
>>
>> > + addr -= OFFSET(inet6_ifaddr_if_list);
>>
>>
>> The above code is easy to understand, because it actually imitates the container_of().
>>
>> But if you would like to have the same style as show_net_devices_v2() and show_net_devices_v3(), that's also fine to me.
Yes, please. I've not seen the above style (do_list and minus OFFSET)
in crash before. Although we may go with the above, I think generally
a new style tends to cause an unexpected result. so I'd like to use
the common style if possible.
Thank you for the comment, Kazu.
I will post it later with the above suggestions.
Thanks.
Lianbo
Thanks,
Kazu
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