Re: How to transfer memory from PCI memory directly to user space safely and portable?

[Philipp Rumpf <prumpf@parcelfarce.linux.theplanet.co.uk>]

On Sun, Nov 26, 2000 at 02:21:31PM +0100, Anders Torger wrote:
> 	memcpy_toio(iobase, user_space_src, count);

I hope count isn't provided by userspace here ?

> 1. What happens if the user space memory is swapped to disk? Will 
> verify_area() make sure that the memory is in physical RAM when it returns, 
> or will it return -EFAULT, or will something even worse happen?

On i386, you'll sleep implicitly waiting for the page fault to be handled;  in
the generic case, anything could happen.

> 2. Is this code really portable? I currently have an I386 architecture, and I 
> could use copy_to/from_user on that instead, but that is not portable. Now, 
> by using memcpy_to/fromio instead, is this code fully portable?

No.  It would be portable if you were using memcpy_fromuser_toio and it
existed.

> 3. Will the current process always be the correct one? The copy functions is 
> directly initiated by the user, and not through an interrupt, so I think the 
> user space mapping will always be to the correct process. Is that correct?

current should be fine if you're not in a bh/interrupt/kernel thread.
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