[RFC,08/29] migration: reuse mis->userfault_quit_fd

It was only used for quitting the page fault thread before. Let it be
something more useful - now we can use it to notify a "wake" for the
page fault thread (for any reason), and it only means "quit" if the
fault_thread_quit is set.

Since we changed what it does, renaming it to userfault_event_fd.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 migration/migration.h    |  6 ++++--
 migration/postcopy-ram.c | 24 ++++++++++++++++--------
 2 files changed, 20 insertions(+), 10 deletions(-)

* Peter Xu (peterx@redhat.com) wrote:
> It was only used for quitting the page fault thread before. Let it be
> something more useful - now we can use it to notify a "wake" for the
> page fault thread (for any reason), and it only means "quit" if the
> fault_thread_quit is set.
> 
> Since we changed what it does, renaming it to userfault_event_fd.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/migration.h    |  6 ++++--
>  migration/postcopy-ram.c | 24 ++++++++++++++++--------
>  2 files changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/migration/migration.h b/migration/migration.h
> index 148c9fa..70e3094 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -35,6 +35,8 @@ struct MigrationIncomingState {
>      bool           have_fault_thread;
>      QemuThread     fault_thread;
>      QemuSemaphore  fault_thread_sem;
> +    /* Set this when we want the fault thread to quit */
> +    bool           fault_thread_quit;
>  
>      bool           have_listen_thread;
>      QemuThread     listen_thread;
> @@ -42,8 +44,8 @@ struct MigrationIncomingState {
>  
>      /* For the kernel to send us notifications */
>      int       userfault_fd;
> -    /* To tell the fault_thread to quit */
> -    int       userfault_quit_fd;
> +    /* To notify the fault_thread to wake, e.g., when need to quit */
> +    int       userfault_event_fd;
>      QEMUFile *to_src_file;
>      QemuMutex rp_mutex;    /* We send replies from multiple threads */
>      void     *postcopy_tmp_page;
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 952b73a..4278fe7 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -305,7 +305,8 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
>           * currently be at 0, we're going to increment it to 1
>           */
>          tmp64 = 1;
> -        if (write(mis->userfault_quit_fd, &tmp64, 8) == 8) {
> +        atomic_set(&mis->fault_thread_quit, 1);
> +        if (write(mis->userfault_event_fd, &tmp64, 8) == 8) {
>              trace_postcopy_ram_incoming_cleanup_join();
>              qemu_thread_join(&mis->fault_thread);
>          } else {
> @@ -315,7 +316,7 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
>          }
>          trace_postcopy_ram_incoming_cleanup_closeuf();
>          close(mis->userfault_fd);
> -        close(mis->userfault_quit_fd);
> +        close(mis->userfault_event_fd);
>          mis->have_fault_thread = false;
>      }
>  
> @@ -438,7 +439,7 @@ static void *postcopy_ram_fault_thread(void *opaque)
>          pfd[0].fd = mis->userfault_fd;
>          pfd[0].events = POLLIN;
>          pfd[0].revents = 0;
> -        pfd[1].fd = mis->userfault_quit_fd;
> +        pfd[1].fd = mis->userfault_event_fd;
>          pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */
>          pfd[1].revents = 0;
>  
> @@ -448,8 +449,15 @@ static void *postcopy_ram_fault_thread(void *opaque)
>          }
>  
>          if (pfd[1].revents) {
> -            trace_postcopy_ram_fault_thread_quit();
> -            break;
> +            uint64_t tmp64 = 0;
> +
> +            /* Consume the signal */
> +            read(mis->userfault_event_fd, &tmp64, 8);
> +
> +            if (atomic_read(&mis->fault_thread_quit)) {
> +                trace_postcopy_ram_fault_thread_quit();
> +                break;
> +            }
>          }
>  
>          ret = read(mis->userfault_fd, &msg, sizeof(msg));
> @@ -528,9 +536,9 @@ int postcopy_ram_enable_notify(MigrationIncomingState *mis)
>      }
>  
>      /* Now an eventfd we use to tell the fault-thread to quit */
> -    mis->userfault_quit_fd = eventfd(0, EFD_CLOEXEC);
> -    if (mis->userfault_quit_fd == -1) {
> -        error_report("%s: Opening userfault_quit_fd: %s", __func__,
> +    mis->userfault_event_fd = eventfd(0, EFD_CLOEXEC);
> +    if (mis->userfault_event_fd == -1) {
> +        error_report("%s: Opening userfault_event_fd: %s", __func__,
>                       strerror(errno));
>          close(mis->userfault_fd);
>          return -1;
> -- 
> 2.7.4
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK