[lwip-devel] Re: [bug #26397] SLIP polling support

[Simon Kallweit]

Kieran Mansley wrote:
> Follow-up Comment #2, bug #26397 (project lwip):
>
> I don't think there's any particular reason why this has failed to be
> applied, just that it hasn't been a high priority.

Ok, then let's look forward to get it included now. Similar work should 
be done on the PPP netif, so it can also be used in a 
polled/single-threaded environment.

> Looking at the patch, it seems to change a lot of code that isn't necessary
> to add the slipif_poll() function.

Well, actually there is not that much code. I think we should try to 
share code for both the polled and the threaded versions, so that's what 
most changes are for.

The struct slipif_priv is used for private data of the SLIP interface, 
as we cannot have them as local variables anymore. The changes in 
slipif_output() are due to the introduced slipif_priv structure. Nothing 
else changed. slipif_input() had to be changed more significantly. The 
old version would block until a new packet was received. The new version 
will return NULL if all data has been read from the serial and no 
complete packet was received, but it will keep track of partially 
received packets, so the next call to slipif_input() can finish the process.

> If you could give more detail about the
> need for the other changes (a good example is the change from sio_read to
> sio_recv) that would help.  Some of the changes are obviously improvements and
> bug fixes, but a lot aren't obvious at first glance to someone not familiar
> with the sio code.

Well, the change from sio_recv() to sio_read() is quite simple, 
sio_recv() directly returns the received character from the serial line 
and is therefore not useable in a polled mode. sio_read() on the other 
hand can return without actually receiving data.

The sio API in general is a bit lacking when it comes to 
blocking/non-blocking operation. I was wondering if it should be 
extended to support some sort of configuration. We should also add some 
documentation I think.

Instead of using sio_read() we could also introduce some method 
sio_peek() to check if there are characters waiting to be received. But 
this would change the API.

Also, in regard to PPP, we should add an API to get/set modem control lines.

> There also seem to be a lot of whitespace changes that make the patch a bit
> harder to read: the whole copyright message for example shouldn't be in the
> patch.

I can remove this. But it's just a bit of cleaning up.

Simon