Re: [PATCH] generic_file_sendpage

["Jörn Engel" <joern@wohnheim.fh-wedel.de>]

On Fri, 15 July 2005 04:06:11 -0700, Andrew Morton wrote:
> > +
> > +	/* There is no sane reason to use O_DIRECT */
> > +	BUG_ON(file->f_flags & O_DIRECT);
> 
> err, this seems like an easy way for people to make the kernel go BUG.

Is there a sane use for O_DIRECT in combination with sendfile()?

If not, I'd like to change sys_sendfile() and return -EINVAL for
O_DIRECT file descriptors.

> > +	if (unlikely(signal_pending(current)))
> > +		return -EINTR;
> 
> This doesn't help.  The reason we've avoided file-to-file sendfile() is
> that it can cause applications to get uninterruptibly stuck in the kernel
> for ages.  This code doesn't solve that problem.  It needs to handle
> signal_pending() inside the main loop.
> 
> And it probably needs to return a sane value (number of bytes copied)
> rather than -EINTR.

Makes sense.

> I don't know if we want to add this feature, really.  It's such a
> specialised thing.

With union mount and cowlink, there are two users already.  cp(1)
could use it as well, even if the improvement is quite minimal.

Jörn

-- 
All art is but imitation of nature.
-- Lucius Annaeus Seneca