Re: [PATCH] generic_file_sendpage

[Herbert Poetzl <herbert@13thfloor.at>]

On Fri, Jul 15, 2005 at 01:22:55PM +0200, Jörn Engel wrote:
> 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.

you might soon add linux-vserver to the list, as
we will be using this for a special version of the
COW links (to break unified links on write) ...

best,
Herbert

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