Re: OT: why no file copy() libc/syscall ??

[jw schultz <jw@pegasys.ws>]

On Fri, Nov 14, 2003 at 12:39:15AM +0100, Andrea Arcangeli wrote:
> On Thu, Nov 13, 2003 at 12:22:14PM -0800, H. Peter Anvin wrote:
> > Followup to:  <20031111085323.M8854@devserv.devel.redhat.com>
> > By author:    Jakub Jelinek <jakub@redhat.com>
> > In newsgroup: linux.dev.kernel
> > > > 
> > > > Actually, I think we should have a: 
> > > > 
> > > > 	long copy_fd_to_fd (int src, int dst, int len)
> > > > 
> > > > type of systemcall. 
> > > 
> > > We have one, sendfile(2).
> > > 
> > 
> > It would be very nice if we could (a) expand the uses of sendfile(2),
> > and (b) have the libc do the fallback to read/write/mmap as needed.
> 
> I actually hacked cp for a while and it improved cp some point percent
> on normal machines.
> 
> See ftp://ftp.suse.com/pub/people/andrea/cp-sendfile/
> 
> the main downside and the reason it wasn't applied IIRC is the lack of
> interruption of sendfile, basically for an huge file it would take a
> while before C^c has any effect. The kernel isn't interrupting the
> syscall.  This is no different from a huge read or write syscall (but
> read/write are never huge or the buffer would need to be huge too, not
> the case for sendfile that works zerocopy), so in theory we could
> workaround it by entering/exiting kernel multiple times just to allow
> the signal to be handled like in the read/write case.

Until interrupt and restart (as has been discussed
here for other syscalls) handling is improved there could be
a sanity check with an E2BIG or something if the size is
insane.  I dislike the thought of sendfile going sitting in D
state on a multi-gigabyte file.

-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw@pegasys.ws

		Remember Cernan and Schmitt