Subject: SOCK_DGRAM and friends

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A diligent student asks:

> Dr. Westall,
>    I'm not sure what exactly is going on, but creating the socket is
> working on note examples that it's not supposed to work for, and not
> working on examples it is supposed to work on.  I was working on
> shadow7.
>
> example: not supposed to work
> [16:42:52] ./hostinfo 2 2 6 5785
> domain = 2, socktype = 2, proto = 6, port = 5785
> s = 3
> done
>
> example: supposed to work
> [16:43:08] ./hostinfo 2 1 6 5785
> domain = 2, socktype = 1, proto = 6, port = 5785
> s = -1
> socket failed: Protocol not supported

The answer is:

That would be because in the solaris  the #defines say

  94 #define  SOCK_STREAM 2     /* stream socket */
  95 #define  SOCK_DGRAM  1     /* datagram socket */
  96 #define  SOCK_RAW 4     /* raw-protocol interface */

  but in Linux the declaration is:

./bits/socket.h:  SOCK_DGRAM = 2,
                  SOCK_STREAM = 1,

Thus its always best to use the "standard name". The relative
strengths of the names is:

IPPROTO_UDP = 17 --- super strong
AF/PF_INET = 2   --- pretty strong
SOCK_DGRAM/STREAM -- pretty weak