Re: Linux 2.6.17-rc2

["Linh Dang" <linhd@nortel.com>]

Jens Axboe <axboe@suse.de> wrote:

> On Thu, Apr 20 2006, Linh Dang wrote:
>> Jens Axboe <axboe@suse.de> wrote:
>>
>>> On Wed, Apr 19 2006, Linus Torvalds wrote:
>>>> There are some other buffer management system calls that I
>>>> haven't done yet (and when I say "I haven't done yet", I
>>>> obviously mean "that I hope some other sucker will do for me,
>>>> since I'm lazy"), but that are obvious future extensions:
>>>
>>> Well it's worked so far, hasn't it? :-)
>>>
>>>> - an ioctl/fcntl to set the maximum size of the buffer. Right now
>>>> it's hardcoded to 16 "buffer entries" (which in turn are normally
>>>> limited to one page each, although there's nothing that
>>>> _requires_ that a buffer entry always be a page).
>>>
>>> This is on a TODO, but not very high up since I've yet to see a
>>> case where the current 16 page limitation is an issue. I'm sure
>>> something will come up eventually, but until then I'd rather not
>>> bother.
>>
>> DVD burning! splicing those huge VOB files into the dvd device
>> would be nice. And believe me, the current 16 entries of the pipe
>> is nowhere enough to sustain burning at 8X avg speed or higher.
>>
>> It's a special case but it'd benefit a LOT of ppl ;-)
>
> (don't drop the cc list)
>
> DVD burning probably isn't a good splice fit, since you need to do
> more than actually just point the device at the data. SG_IO is
> already zero-copy as it maps the user data into the kernel without
> copying, so there's very little room for improvement there to begin
> with.

DVD burning on linux is mostly:

        mkisofs .... | growisofs ....

Ideally, on mkisofs side, we'd be able to:

  - write some data/padding into the pipe
  - splice a HUGE file into the pipe
  - write some data/padding into the pipe
  - splice a HUGE file into the pipe
  ...

On growisofs side, we'd be able to:

  - send some commands
  - splice N MBs of data from the pipe to the driver
  - send some commands
  - splice M MBs of data from the pipe to the driver
  ...

What'd be nice is an ioctl to change the size of the pipe between
mkisofs and growisofs.

--
Linh Dang
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