Re: sendfile(2) behaviour has changed ?

["David S. Miller" <davem@redhat.com>]

   From: Matti Aarnio <matti.aarnio@zmailer.org>
   Date: Wed, 16 Oct 2002 12:10:46 +0300

   On Wed, Oct 16, 2002 at 10:49:08AM +0200, Zilvinas Valinskas wrote:
   > Is this expected behaviour ? that sendfile(2) on 2.5.4x linux kernel requires
   > socket as an output fd paramter ? 
   
     It has only been intended for output to a TCP stream socket.

To be honest, I'm not so sure about this.

For example, I definitely see us supporting this in the
opposite direction when commodity 10gbit hits the market.

Initially I thought "sys_receivefile()" but it makes no
sense when we have a system call that is perfectly capable
of describing the tcp_socket --> page_cache operation.

And I don't think the vfs copy operation using sendfile
is such a bad thing either.  It definitely opens the door
for some interesting optimizations.  For example, if the
source page is not mapped by a process it could be possible
to just unhash it, mark it dirty, then hash it into the
destination file.  Exactly 2 I/O operations and the cpu
doesn't touch the data at all.