Re: [Lksctp-developers] Some Bugs?

[Sridhar S. <sr...@us...>]

On Sun, 21 Mar 2004, Michael Tuexen wrote:

> Dear all,
>
> I'm using the 2.6.2 kernel.
>
> It seems that the Linux SCTP implementation does some little/big
> endian byte order transformation of the PPID field. From the ID:
>
>     sinfo_ppid: 32 bits (unsigned integer)
>
>     This value in sendmsg() is an opaque unsigned value that is passed to
>     the remote end in each user message.  In recvmsg() this value is the
>     same information that was passed by the upper layer in the peer
>     application.  Please note that byte order issues are NOT accounted
>     for and this information is passed opaquely by the SCTP stack from
>     one end to the other.
>
> Therefore the user has to call htonl() by himself.
>
> To reproduce the problem you can use the following Scheme Code,
> translation
> to C is trivial:
>
> (define s (socket AF_INET SOCK_STREAM IPPROTO_SCTP))
> (connect s AF_INET (inet-aton "192.168.1.30") 5555)
> (sctp-sendmsg s "Hallo" 1 0 0 0 AF_INET (inet-aton "192.168.1.30") 5555)
> (sctp-sendmsg s "Hallo" (ntohl  1) 0 0 0 AF_INET (inet-aton
> "192.168.1.30") 5555)
>
> The first message shows an incorrect PPID on the wire whereas the
> second shows
> the correct. So I assume that you call htonl() in your code.

Yes. We do a htonl() before sending and a ntohl() after receiving the chunk.
This does conflict with the above sinfo_ppid description from the API draft.

So an application needs to do a htonl() on the ppid, but should not do a
htons() on the stream_no passed to sctp_sendmsg(). Isn't it little confusing?

>
> The next problem is that for a 1-1 style socket I would think that I
> can use
> (sctp-sendmsg s "Hallo" 1 0 0 0 AF_INET INADDR_ANY 0)
> because the destination address and port is known. sctp-sendmsg returns
> an error.
> This should not occur.

I guess here sctp_sendmsg() is called on on a connected 1-1 style socket.
Currently it is OK to pass a NULL destination address, but you get an error
if you pass an invalid or INADDR_ANY address.
I think the right behavior is to ignore the destination address on a
connected 1-1 style socket or a peeled-off socket. This needs to be fixed.

>
> The last problem I found is that the following code just works:
> (define s (socket AF_INET SOCK_STREAM IPPROTO_SCTP))
> (sctp-sendmsg s "Hallo" 1 0 0 0 AF_INET (inet-aton "192.168.1.30") 5555)
>
> I think there should be an error returned, because the socket is not
> connected.

This is due to the fact that lksctp supports auto-connect even on a 1-1 style
socket. This enables bundling of data with cookie-echo.
I hope this is OK unless there are any negative sideeffects with auto-connect
on 1-1 style socket.

Thanks
Sridhar

>
> Best regards
> Michael
>
> PS.: The examples are given in scheme, which just wraps the
> corresponding C functions.
>
>
>
>
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