Re: Is sendfile all that sexy?

[Linus Torvalds]

In article <[e-mail]>,
Ben Mansell  <[e-mail]> wrote:
>On 14 Jan 2001, Linus Torvalds wrote:
>
>> And no, I don't actually hink that sendfile() is all that hot. It was
>> _very_ easy to implement, and can be considered a 5-minute hack to give
>> a feature that fit very well in the MM architecture, and that the Apache
>> folks had already been using on other architectures.
>
>The current sendfile() has the limitation that it can't read data from
>a socket. Would it be another 5-minute hack to remove this limitation, so
>you could sendfile between sockets? Now _that_ would be sexy :)

I don't think that would be all that sexy at all.

You have to realize, that sendfile() is meant as an optimization, by
being able to re-use the same buffers that act as the in-kernel page
cache as buffers for sending data. So you avoid one copy.

However, for socket->socket, we would not have such an advantage.  A
socket->socket sendfile() would not avoid any copies the way the
networking is done today.  That _may_ change, of course.  But it might
not.  And I'd rather tell people using sendfile() that you get EINVAL if
it isn't able to optimize the transfer.. 

		Linus