tiny tty driver sample

tiny tty driver sample

[Jon Ringle]

Hello,

I'm trying to write a tty driver and I'm using
http://lwn.net/images/pdf/LDD3/ch18.pdf as a guide. The sample tiny tty
driver includes the following code:

            for (i = 0; i < data_size; ++i) {
                        if (tty->flip.count >= TTY_FLIPBUF_SIZE)
                                    tty_flip_buffer_push(tty);
                        tty_insert_flip_char(tty, data[i], TTY_NORMAL);
            }
            tty_flip_buffer_push(tty);

This doesn't compile against Linux 2.6.16 kernel I'm using, because
tty->flip.count doesn't exist anymore.
How should this sample be re-coded?

Thanks,

Jon

Re: tiny tty driver sample

[Jiri Kosina]

On Wed, 7 Mar 2007, Jon Ringle wrote:

> I'm trying to write a tty driver and I'm using 
> http://lwn.net/images/pdf/LDD3/ch18.pdf as a guide. The sample tiny tty 
> driver includes the following code:
>             for (i = 0; i < data_size; ++i) {
>                         if (tty->flip.count >= TTY_FLIPBUF_SIZE)
>                                     tty_flip_buffer_push(tty);
>                         tty_insert_flip_char(tty, data[i], TTY_NORMAL);
>             }
>             tty_flip_buffer_push(tty);
> This doesn't compile against Linux 2.6.16 kernel I'm using, because 
> tty->flip.count doesn't exist anymore. How should this sample be 
> re-coded?

I guess something like

	tty_buffer_request_room(tty, data_size);
	for (i = 0; i < data_size; ++i)
		work += tty_insert_flip_char(tty, data[i], TTY_NORMAL);
	if (work)
		tty_flip_buffer_push(tty);

will do.

-- 
Jiri Kosina

Re: tiny tty driver sample

[Alan Cox]

> I guess something like
> 
> 	tty_buffer_request_room(tty, data_size);
> 	for (i = 0; i < data_size; ++i)
> 		work += tty_insert_flip_char(tty, data[i], TTY_NORMAL);
> 	if (work)
> 		tty_flip_buffer_push(tty);


Unless data_size can be very large and high speed then you can replace the
lot with

	if (tty_insert_flip_string(tty, data, data_size))
		tty_flip_buffer_push(tty);

Re: tiny tty driver sample

[H. Peter Anvin]

Alan Cox wrote:
>> I guess something like
>>
>> 	tty_buffer_request_room(tty, data_size);
>> 	for (i = 0; i < data_size; ++i)
>> 		work += tty_insert_flip_char(tty, data[i], TTY_NORMAL);
>> 	if (work)
>> 		tty_flip_buffer_push(tty);
> 
> 
> Unless data_size can be very large and high speed then you can replace the
> lot with
> 
> 	if (tty_insert_flip_string(tty, data, data_size))
> 		tty_flip_buffer_push(tty);
> 

What does "very large and high speed" mean in this context?

	-hpa

Re: tiny tty driver sample

[Alan Cox]

> > Unless data_size can be very large and high speed then you can replace the
> > lot with
> > 
> > 	if (tty_insert_flip_string(tty, data, data_size))
> > 		tty_flip_buffer_push(tty);
> > 
> 
> What does "very large and high speed" mean in this context?

The default behaviour is to generate buffers based upon perceived need
and then cycle them, so you tend to get chunks of 512 bytes or so. The
logic is abstracted into tty_buffer_find() so can easily be changed.

Some hardware at high speeds with big FIFOs (or virtualised interfaces)
produces big chunks of data in blocks with the size known at read time (eg
that with large fifos and 100 polls/sec) - for those you can avoid
generating a series of allocations or buffers by using the request_room
interface to hint the size of the buffer you will actually need.

Re: tiny tty driver sample

[Jiri Slaby]

Jon Ringle napsal(a):
> Hello,
> 
> I'm trying to write a tty driver and I'm using
> http://lwn.net/images/pdf/LDD3/ch18.pdf as a guide. The sample tiny tty
> driver includes the following code:
> 
>             for (i = 0; i < data_size; ++i) {
>                         if (tty->flip.count >= TTY_FLIPBUF_SIZE)
>                                     tty_flip_buffer_push(tty);
>                         tty_insert_flip_char(tty, data[i], TTY_NORMAL);
>             }
>             tty_flip_buffer_push(tty);
> 
> This doesn't compile against Linux 2.6.16 kernel I'm using, because
> tty->flip.count doesn't exist anymore.
> How should this sample be re-coded?

I think this way:
http://lkml.org/lkml/2007/2/17/65

regards,
-- 
http://www.fi.muni.cz/~xslaby/            Jiri Slaby
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E