GSoC 2017 Introduction: Netlink socket parsers

[JingPiao Chen]

On Tue, Mar 28, 2017 at 10:37 AM, Dmitry V. Levin wrote:
>On Mon, Mar 27, 2017 at 10:40:05PM +0800, JingPiao Chen wrote:
>> 2017-03-27 6:16 GMT+08:00 Dmitry V. Levin <ldv at ...> 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.
>
>Sorry, I don't understand.  Do you mean that you haven't seen a commit big
>enough to make review a herculean job?

No, I lack of the experience of code review, don't know review a big commit
is a herculean job, sorry.

>
>> I think all this commits
>> implement enhance netlink socket decode.
>> Do you think separate three commits, or can you give me some advice?
>
>The general idea is that every logically separate change goes
>to an individual commit.
>The netlink branch made by Fabien follows this approach.
>Can you follow it, too?
Ok.
>
>> 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.
>
>Sorry, I don't understand, is it something you've done already,
>or are you going to implement this?
>
>> >> (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.
>
>Are you absolutely sure that in *all* cases the descriptor is passed
>via the 1st syscall argument?
>
>The common rule is not to make such assumptions unless you are 100% sure.
>
>> >> 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
>
>Why do you want to rewrite getfdnlproto?
>What's wrong with optional_data?

They are right. I rewirte them because they changed a lot of previous code,
not easy to review.

Thank you.
--
JingPiao Chen
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