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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <20150714151538.GA13856@work-vm> (David Alan Gilbert's message of
	"Tue, 14 Jul 2015 16:15:39 +0100")
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Date: Tue, 14 Jul 2015 17:25:20 +0200
Message-ID: <87r3oaep7j.fsf@neno.neno>
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Subject: Re: [Qemu-devel] [PATCH v7 37/42] Postcopy;
	Handle userfault requests
Reply-To: quintela@redhat.com
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To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: aarcange@redhat.com, yamahata@private.email.ne.jp, liang.z.li@intel.com, qemu-devel@nongnu.org, luis@cs.umu.se, amit.shah@redhat.com, pbonzini@redhat.com, david@gibson.dropbear.id.au

"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> * Juan Quintela (quintela@redhat.com) wrote:
>> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
>> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>> >
>> > userfaultfd is a Linux syscall that gives an fd that receives a stream
>> > of notifications of accesses to pages registered with it and allows
>> > the program to acknowledge those stalls and tell the accessing
>> > thread to carry on.
>> >
>> > We convert the requests from the kernel into messages back to the
>> > source asking for the pages.
>> >
>> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>> 
>> 
>> > @@ -274,15 +276,41 @@ int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
>> >   */
>> >  int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
>> >  {
>> > -    /* TODO: Join the fault thread once we're sure it will exit */
>> > -    if (qemu_ram_foreach_block(cleanup_area, mis)) {
>> > -        return -1;
>> > +    trace_postcopy_ram_incoming_cleanup_entry();
>> > +
>> > +    if (mis->have_fault_thread) {
>> > +        uint64_t tmp64;
>> > +
>> > +        if (qemu_ram_foreach_block(cleanup_area, mis)) {
>> > +            return -1;
>> > +        }
>> > +        /*
>> > +         * Tell the fault_thread to exit, it's an eventfd that should
>> > +         * currently be at 0, we're going to inc it to 1
>> > +         */
>> > +        tmp64 = 1;
>> > +        if (write(mis->userfault_quit_fd, &tmp64, 8) == 8) {
>> > +            trace_postcopy_ram_incoming_cleanup_join();
>> > +            qemu_thread_join(&mis->fault_thread);
>> > +        } else {
>> > +            /* Not much we can do here, but may as well report it */
>> > +            error_report("%s: incing userfault_quit_fd: %s", __func__,
>> > +                         strerror(errno));
>> 
>> "incing"???
>
> Oh, incrementing :-)
> Changed.
>
> Dave
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Reviewed-by: Juan Quintela <quintela@redhat.com>