Re: sendfile

From: Pål Halvorsen (paalh@ifi.uio.no)
Date: Wed Apr 30 2003 - 14:12:17 EST


On Wed, 30 Apr 2003, bert hubert wrote:

> > Does sendfile support UDP connections (SOCK_DGRAM)?
>
> Try it. I bet it doesn't do so, and certainly not usably. Blasting UDP
> frames is seldomly useful without checks, like NFS performs.

It could be useful for applications like streaming video where other
protocols on top provide additional functionality or in a multicast
session where TCP migth not be appropriate.

> > Does sendfile remove ALL in-memory data copy operations?
>
> Depends. With some network adaptors it might. Definition of 'zero-copy' is
> somewhat misty. Some variants of zero-copy would actually be called
> 'one-copy' or 'minus-one-copy' in other contexts.

But should not the 2.4.X kernels have support for chained sk_buffs (like
the BSD mbufs) meaning that support for scatter-gatter I/O from the NIC
should be unneccessary to support zero-copy (i.e., NO in-memory data
copy operations)?

> Regards,
>
> bert

Cheers,
-ph
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