Re: [Xen-devel] [PATCH] Add SCHEDOP_block_on

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 10 Mar 2006, at 15:34, John Levon wrote:

> This patch adds a facility to block on a particular event channel, for
> when a domain needs to block, but cannot enable interrupts.
I really don't much like the change this adds to evtchn_set_pending(), 
particularly since this patch probably doesn't have general 
applicability beyond debuggers. I wonder if you could get the 
functionality you need with the existing SCHEDOP_block interface if you 
do the following:
        HYPERVISOR_set_callbacks(<dummy irq handler>);
        clear_evtchn_mask(evtchn);
        while (1) {
		/* Important to clear the master flag /then/ selector /then/ evtchn 
pending. */
                vcpu_info->evtchn_upcall_pending = 0;
                clear_bit(evtchn, &vcpu_info->evtchn_pending_sel);
                clear_evtchn_pending(evtchn);
                if (check_for_data(evtchn))
                        break;
                HYPERVISOR_block();
        }

Where dummy_irq_handler is a no-op return (which should probably return 
leaving event delivery disabled, to prevent event-delivery storm, thus 
it probably really is just IRET).
Certainly the above should work fine for a post-mortem debugger. Even 
if you need to be able to exit the debugger and continue executing 
normal kernel code, we can come up with some suitable code to restore 
normal event delivery without Xen interface changes.
 -- Keir


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