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SubjectRe: RFC: i386: kill !4KSTACKS
On Tuesday 06 September 2005 18:28, Roland Dreier wrote:
> Daniel> There are only two stacks involved, the normal kernel
> Daniel> stack and your new ndis stack. You save ESP of the kernel
> Daniel> stack at the base of the ndis stack. When the Windows
> Daniel> code calls your api, you get the ndis ESP, load the kernel
> Daniel> ESP from the base of the ndis stack, push the ndis ESP so
> Daniel> you can get back to the ndis code later, and continue on
> Daniel> your merry way.
> [...]
> Daniel> You will allocate your own stack once on driver
> Daniel> initialization.
> I'm not quite sure it's this trivial. Obviously there are more than
> two stacks involved, since there is more than one kernel stack! (One
> per task plus IRQ stacks) This is more than just a theoretical
> problem. It seems entirely possible that more than one task could
> be in the driver, and clearly they each need their own stack.

Semaphore :-)

Do you expect this to be heavily contended? On a very quick run through the
code, it seems you don't hold any spinlocks going into the driver from
process context. Interrupts... they better fit into a 4K stack or it's game
over. Preemption while on the ndis stack... you can always disable
preemption in this region, but the semaphore should protect you. Task killed
while preempted... I dunno.

> So it's going to be at least a little harder than allocating a single
> stack for NDIS use when the driver starts up.
> I personally like the idea raised elsewhere in this thread of running
> the Windows driver in userspace by proxying interrupts, PCI access,
> etc. That seems more robust and probably allows some cool reverse
> engineering hacks.

I expect the userspace approach will be a lot more work and a lot more
overhead too, but then again it sounds like loads of fun.


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