On 02/07/2012 07:40 AM, Alexander Graf wrote:
Why? For the HPET timer register for example, we could have a simple MMIO hook
that says
on_read:
return read_current_time() - shared_page.offset;
on_write:
handle_in_user_space();
For IDE, it would be as simple as
register_pio_hook_ptr_r(PIO_IDE, SIZE_BYTE,&s->cmd[0]);
for (i = 1; i< 7; i++) {
register_pio_hook_ptr_r(PIO_IDE + i, SIZE_BYTE,&s->cmd[i]);
register_pio_hook_ptr_w(PIO_IDE + i, SIZE_BYTE,&s->cmd[i]);
}
You can't easily serialize updates to that address with the kernel since two
threads are likely going to be accessing it at the same time. That either means
an expensive sync operation or a reliance on atomic instructions.
But not all architectures offer non-word sized atomic instructions so it gets
fairly nasty in practice.
Regards,
Anthony Liguori
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