Re: [Qemu-devel] [PATCH v7 37/42] Postcopy; Handle userfault requests

[Juan Quintela]

"Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> 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 <address@hidden>


> @@ -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"???