[PATCH v3 2/2] virtio-blk: Convert QEMUBH callback to "bitops.h" API

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

By directly using find_first_bit() and find_next_bit from the
"bitops.h" API to iterate over the bitmap, we can remove the
bitmap[] variable-length array copy on the stack and the complex
manual bit testing/clearing logic.

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index e9050c8987e..a31fa94ca33 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -60,24 +60,14 @@ static void notify_guest_bh(void *opaque)
 {
     VirtIOBlockDataPlane *s = opaque;
     unsigned nvqs = s->conf->num_queues;
-    unsigned long bitmap[BITS_TO_LONGS(nvqs)];
-    unsigned j;
 
-    memcpy(bitmap, s->batch_notify_vqs, sizeof(bitmap));
-    memset(s->batch_notify_vqs, 0, sizeof(bitmap));
+    for (unsigned long i = find_first_bit(s->batch_notify_vqs, nvqs);
+             i < nvqs; i = find_next_bit(s->batch_notify_vqs, nvqs, i)) {
+        VirtQueue *vq = virtio_get_queue(s->vdev, i);
 
-    for (j = 0; j < nvqs; j += BITS_PER_LONG) {
-        unsigned long bits = bitmap[j / BITS_PER_LONG];
-
-        while (bits != 0) {
-            unsigned i = j + ctzl(bits);
-            VirtQueue *vq = virtio_get_queue(s->vdev, i);
-
-            virtio_notify_irqfd(s->vdev, vq);
-
-            bits &= bits - 1; /* clear right-most bit */
-        }
+        virtio_notify_irqfd(s->vdev, vq);
     }
+    bitmap_clear(s->batch_notify_vqs, 0, nvqs);
 }
 
 /* Context: QEMU global mutex held */
-- 
2.26.3