Re: Running user processes in kernel mode; Java and .NETsupport in kernel

[Alan Cox]

On Llu, 2004-10-18 at 20:50, Kendall Bennett wrote:
> Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> > Why would I care ? I need the MMU for paging and to avoid
> > fragmentation of the system. If I have the MMU on then memory
> > protection checks are free. 
> > 
> > Except in 4G/4G mode syscalls are extremely cheap too nowdays.
> 
> Yes, but kernel mode support in user programs would allow user mode 
> device drivers to do stuff that currently cannot be done at all from user 
> space such as handling interrupts and scheduling DMA operations.

DMA doesn't need the kernel's help except for when you want to manage
security - DRI is quite special in that way. A driver to provide
mmapable DMA memory is trivial. IRQ's are *much* harder because you have
to clear the IRQ source in the IRQ handler, but people have code that
does this and then sends signals.

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