Re: [PATCH] generic_file_sendpage

[Linus Torvalds <torvalds@osdl.org>]

On Fri, 15 Jul 2005, Jan Engelhardt wrote:
> >
> >This is why I want to get rid of sendfile(). It's a fundamentally broken
> >interface. Really. In contrast, the pipe buffers _can_ be used for direct
> >socket->file interfaces.
> 
> How will userspace access these pipe buffers?

You can fill them from a user-space buffer with "write()", and you can
read them into a user-space buffer with "read()".

It's really a pipe.

The idea of the pipe buffers is that you can _also_ send them to other 
file descriptors, or fill them from other file descriptors, without having 
to copy the data to/from user space.

		Linus

---
See the example patch that I posted months ago (and that I referred to in 
my other email, here is that thing repeated in case you missed it):

> For anybody interested in zero-copy work, here's a LWN write-up of some of
> the original discussion:
> 
>         http://lwn.net/Articles/118750/
> 
> and my (very ugly) example patch can be found for example here:
> 
>         http://groups-beta.google.com/group/linux.kernel/msg/782bd9e5cb647207?hl=en&;
> 
> (it's not a a complete implementation, but it shows how to go from a file
> _to_ a pipe buffer, but not back to a file again).

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