[lwip-devel] [patch #8882] Vector improvements

[Joel Cunningham]

Follow-up Comment #14, patch #8882 (project lwip):

Simon,

I like the idea of treating the set of vectors the same for both UDP and TCP
but I think adding support for TCP sending to lwip_netconn_do_send() is going
to be complicated if we don't use/re-use logic from
lwip_netconn_do_writemore()

do_writemore() has all the infrastructure to block the caller during a partial
write and then callback during poll_tcp() and sent_tcp() to continue sending. 
Non-blocking would be easy, as we just return the partial number of bytes,
it's the blocking that is challenging.

What do you think about modifying lwip_netconn_do_writemore() to use a netbuf
pointer instead of a void *?  We currently have the following state in struct
api_msg:


/** used for lwip_netconn_do_write */
    struct {
      const void *dataptr;
      size_t len;
      u8_t apiflags;
#if LWIP_SO_SNDTIMEO
      u32_t time_started;
#endif /* LWIP_SO_SNDTIMEO */
    } w;


Since the netbuf would be on the callers stack, we wouldn't need to increase
the size of struct api_msg.  We could then modify lwip_netconn_do_writemore()
to operate on a netbuf containing one or more pbufs.  I think the only thing
that would change in the normal send case is that netconn_write_partly() would
need to assign dataptr to a netbuf via netbuf_ref() (like is currently done
for UDP sendto)

This work would also start laying the ground work for having tcp_write()
accept pbufs directly as we'd already have the top end working with pbufs,
then later tcp_write could be improved to also support pbufs.

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