[PATCH 2/3] Support unix sockets in -yy option

[Masatake YAMATO]

Thank you for reviewing.

>> This patch extends -yy option; the peer address of a unix socket can be
>> printed like an inet socket.
>> 
>> About a listening socket, its socket path and socket inode are printed.
>> About an accepted socket, its socket path, socket inode and peer inode
>> are printed.
>> About a client socket, its socket inode and peer inode are printed.
>> 
>> An example of server side with netcat:
>> 
>>    $ ./strace -yy -e network nc -l -U /tmp/example.sock
>>    socket(PF_LOCAL, SOCK_STREAM, 0)        = 3
>>    setsockopt(3<UNIX:[12592606]>, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
>>    bind(3<UNIX:[12592606]>, {sa_family=AF_LOCAL, sun_path="/tmp/example.sock"}, 19) = 0
>>    listen(3</tmp/example.sock,12592606>, 10) = 0
>>    accept(3</tmp/example.sock,12592606>, {sa_family=AF_LOCAL, NULL}, [2]) = 4</tmp/example.sock,12593212->12591974>
>>    recvfrom(4</tmp/example.sock,12593212->12591974>, "INPUT\n", 8192, 0, NULL, NULL) = 6
> 
> I see potential source of confusion in this output format: socket path
> looks very similar to a regular file path.  Lets change it somehow to
> avoid ambiguity.  For example, we could add "UNIX:" prefix:
> 
> 	3<UNIX:/tmp/example.sock,12592606>
> 
> For the same reason, maybe the inode information is better to be added
> before the path rather than after the path, e.g.
> 
> 	4<UNIX:12593212->12591974:/tmp/example.sock>

How about following format:

    FD "<UNIX:[" SELF_INODE [ "->" PEER_INODE ] [ ":" PATH ] "]>"

(I used double quotes here because "[" and "]" are used as literal and meta characters.)

e.g.

    % ./strace -yy -e network nc -l -U /tmp/example.socket
    socket(PF_LOCAL, SOCK_STREAM, 0)        = 3
    setsockopt(3<UNIX:[14672314]>, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
    bind(3<UNIX:[14672314]>, {sa_family=AF_LOCAL, sun_path="/tmp/example.socket"}, 21) = 0
    listen(3<UNIX:[14672314:/tmp/example.socket]>, 10) = 0
    accept(3<UNIX:[14672314:/tmp/example.socket]>, {sa_family=AF_LOCAL, NULL}, [2]) = 4<UNIX:[14672333->14672331:/tmp/example.socket]>
    recvfrom(4<UNIX:[14672333->14672331:/tmp/example.socket]>, "a\n", 8192, 0, NULL, NULL) = 2

Using "[" and "]" as literal characters is verbose but the output
format is uniformed well in listening, accepted sockets and other protocol
of sockets like netlink.

Masatake YAMATO