GSoC 2017 Introduction: Netlink socket parsers

[JingPiao Chen]

>Hi,
2017-03-27 6:16 GMT+08:00 Dmitry V. Levin <ldv at altlinux.org> wrote:
>On Sun, Mar 19, 2017 at 12:25:11PM +0800, JingPiao Chen wrote:
>> Hello strace-developers:
>> My name is JingPiao Chen. I'am a Computer Science sophomore from
>> Guangdong Pharmaceutical University. I am interested in Netlink socket
>> parsers suggested by Gabriel Laskar and Dmitry V. Levin. I am familiar
>> with C, git, shell script, and gdb.
>>
>> My current work base on the code by Fabien Siron
>> (https://github.com/Saruta/strace/tree/netlink)
>
>btw, there was a short conversation on #strace a month ago about this code:
>https://strace.io/logs/strace/2017-02-28
>
>> The work I do:
>> (master:https://github.com/ppiao/strace/tree/master)
>> 1.Merge it into latest main tree.
>> 2.Fix coding style.
>> 3.Rewrite decode_netlink_flags() and decode_netlink_type().
>> 4.Rewrite and rename decode_inet_diag_sockid().
>> 5.Rewrite decode_nlattr_data().
>> 6.Decode some nested attributes.
>
>Why have you squashed all commits made by Fabien into a single commit?
>Do you think it's easier to review a big commit rather than a series of
>small commits?
>

No, I don't know a big commit not easy to review. I think all this commits
implement enhance netlink socket decode.
Do you think separate three commits, or can you give me some advice?
1.Add support for NLMSG_ERROR and NLMSG_DONE.
2.Introduce getfdnlproto and enhanced decoding of struct nlmsghdr
nlmsg_type and nlmsg_flags.
3.Introduce a dummy netlink attributes parser and decoding of
NETLINK_SOCK_DIAG protocol.

>> (netlink branch:https://github.com/ppiao/strace/tree/netlink)
>> 7.Rewrite getfdnlproto().
>> 8.Do not use optional_data in struct print_iovec_config,
>> when call print_iovec, pass tcp->u_arg[0] as fd.
>> Is this right? Like this:
>>
>> diff --git a/io.c b/io.c
>> index a4f6b8e..6b43d7d 100644
>> --- a/io.c
>> +++ b/io.c
>> @@ -94,7 +94,7 @@ print_iovec(struct tcb *tcp, void *elem_buf, size_t
>> elem_size, void *data)
>>   len = c->data_size;
>>   if (c->data_size != (kernel_ulong_t) -1)
>>   c->data_size -= len;
>> - decode_netlink(tcp, iov[0], iov[1]);
>> + decode_netlink(tcp, tcp->u_arg[0], iov[0], iov[1]);
>
>Why tcp->u_arg[0]?  It doesn't look correct.

Because send, sendto, recv, recvfrom, sendmsg, sendmmsg, recvmsg and
recvmmsg
the first argument are fd.

>> I want to know the goal of Netlink socket parsers project.
>
>Obviously, the goal is to implement parsers for assigned netlink families.
I upload a draft of my proposal[1]. Please provide some feedback.
Thank you.

[1]
https://docs.google.com/document/d/15cVdpdBP6jzEGP74tSG18ymi278_P2uv8MhRus-CuPI/edit?usp=sharing
--
JingPiao Chen
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