mtd comments

Alexander Larsson alex at
Tue Mar 14 12:23:26 EST 2000

On Tue, 14 Mar 2000, David Woodhouse wrote:

> > > If they're actually called with a kernel-space buffer, we use 
> > > set_fs(KERNEL_DS) beforehand, which handles the rest of your question.
> alex at said:
> > Oh, i didn't know about that trick. Well that seems like a good idea
> > then. I suppose we have to fix all driver too. 
> I'm not convinced that this is such a good idea. While copy_to_user() is free
> on decent CPUs, we expect people to be using 386en for embedded systems, and
> copy_to_user() is unnecessary overhead. 
> The only front end which copies directly to userspace is the chardevice, isn't 
> it? Everything else copies to kernel-space. As the chardevice is mainly a 
> hacking and config tool - it's generally only used to put the filesystem on 
> the device in the first place - I think it's best to slow it down rather than 
> slowing down everything else - i.e. to make it allocate buffers and copy to 
> userspace itself.


/ Alex

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