[V2][PATCH 1/1] lockable: use QLNULL for a null lockable

[V2][PATCH 1/1] lockable: use QLNULL for a null lockable

[Joe Slater]

Allows us to build with -Og and optimizations that
do not clean up dead-code.

If we use QLNULL for null lockables, we can always
use referencing unknown_lock_type as a link time
error indicator.

Signed-off-by: Joe Slater <joe.slater@windriver.com>
---
 include/qemu/lockable.h        | 20 ++++++++------------
 block/block-backend.c          |  4 ++--
 block/block-copy.c             |  2 +-
 block/mirror.c                 |  4 ++--
 fsdev/qemu-fsdev-throttle.c    |  6 +++---
 hw/9pfs/9p.c                   |  2 +-
 util/qemu-co-shared-resource.c |  2 +-
 7 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/include/qemu/lockable.h b/include/qemu/lockable.h
index b620023..b928de0 100644
--- a/include/qemu/lockable.h
+++ b/include/qemu/lockable.h
@@ -24,18 +24,14 @@ struct QemuLockable {
     QemuLockUnlockFunc *unlock;
 };
 
-/* This function gives an error if an invalid, non-NULL pointer type is passed
- * to QEMU_MAKE_LOCKABLE.  For optimized builds, we can rely on dead-code elimination
- * from the compiler, and give the errors already at link time.
+/*
+ *  If unknown_lock_type() is referenced, it means we have tried to passed something
+ *  not recognized as lockable to the macros below.  Use QLNULL to intentionally pass
+ *  a null lockable.  Using NULL will cause (unused) references to unknown_lock_type()
+ *  which may or may not be eliminated by optimization.
  */
-#if defined(__OPTIMIZE__) && !defined(__SANITIZE_ADDRESS__)
+#define QLNULL ((QemuLockable *)NULL)
 void unknown_lock_type(void *);
-#else
-static inline void unknown_lock_type(void *unused)
-{
-    abort();
-}
-#endif
 
 static inline __attribute__((__always_inline__)) QemuLockable *
 qemu_make_lockable(void *x, QemuLockable *lockable)
@@ -46,7 +42,7 @@ qemu_make_lockable(void *x, QemuLockable *lockable)
     return x ? lockable : NULL;
 }
 
-/* Auxiliary macros to simplify QEMU_MAKE_LOCABLE.  */
+/* Auxiliary macros to simplify QEMU_MAKE_LOCKABLE.  */
 #define QEMU_LOCK_FUNC(x) ((QemuLockUnlockFunc *)    \
     QEMU_GENERIC(x,                                  \
                  (QemuMutex *, qemu_mutex_lock),     \
@@ -79,7 +75,7 @@ qemu_make_lockable(void *x, QemuLockable *lockable)
  *
  * Returns a QemuLockable object that can be passed around
  * to a function that can operate with locks of any kind, or
- * NULL if @x is %NULL.
+ * NULL if @x is %QLNULL.
  */
 #define QEMU_MAKE_LOCKABLE(x)                        \
     QEMU_GENERIC(x,                                  \
diff --git a/block/block-backend.c b/block/block-backend.c
index 6936b25..92128e8 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -1174,7 +1174,7 @@ static void coroutine_fn blk_wait_while_drained(BlockBackend *blk)
 
     if (blk->quiesce_counter && !blk->disable_request_queuing) {
         blk_dec_in_flight(blk);
-        qemu_co_queue_wait(&blk->queued_requests, NULL);
+        qemu_co_queue_wait(&blk->queued_requests, QLNULL);
         blk_inc_in_flight(blk);
     }
 }
@@ -2367,7 +2367,7 @@ static void blk_root_drained_end(BdrvChild *child, int *drained_end_counter)
         if (blk->dev_ops && blk->dev_ops->drained_end) {
             blk->dev_ops->drained_end(blk->dev_opaque);
         }
-        while (qemu_co_enter_next(&blk->queued_requests, NULL)) {
+        while (qemu_co_enter_next(&blk->queued_requests, QLNULL)) {
             /* Resume all queued requests */
         }
     }
diff --git a/block/block-copy.c b/block/block-copy.c
index bb8d056..8de0b54 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -120,7 +120,7 @@ static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t offset,
         return false;
     }
 
-    qemu_co_queue_wait(&task->wait_queue, NULL);
+    qemu_co_queue_wait(&task->wait_queue, QLNULL);
 
     return true;
 }
diff --git a/block/mirror.c b/block/mirror.c
index e8e8844..db5c44e 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -157,7 +157,7 @@ static void coroutine_fn mirror_wait_on_conflicts(MirrorOp *self,
             if (ranges_overlap(self_start_chunk, self_nb_chunks,
                                op_start_chunk, op_nb_chunks))
             {
-                qemu_co_queue_wait(&op->waiting_requests, NULL);
+                qemu_co_queue_wait(&op->waiting_requests, QLNULL);
                 break;
             }
         }
@@ -297,7 +297,7 @@ mirror_wait_for_any_operation(MirrorBlockJob *s, bool active)
         if (!op->is_pseudo_op && op->is_in_flight &&
             op->is_active_write == active)
         {
-            qemu_co_queue_wait(&op->waiting_requests, NULL);
+            qemu_co_queue_wait(&op->waiting_requests, QLNULL);
             return;
         }
     }
diff --git a/fsdev/qemu-fsdev-throttle.c b/fsdev/qemu-fsdev-throttle.c
index 5c83a1c..78d256d 100644
--- a/fsdev/qemu-fsdev-throttle.c
+++ b/fsdev/qemu-fsdev-throttle.c
@@ -22,13 +22,13 @@
 static void fsdev_throttle_read_timer_cb(void *opaque)
 {
     FsThrottle *fst = opaque;
-    qemu_co_enter_next(&fst->throttled_reqs[false], NULL);
+    qemu_co_enter_next(&fst->throttled_reqs[false], QLNULL);
 }
 
 static void fsdev_throttle_write_timer_cb(void *opaque)
 {
     FsThrottle *fst = opaque;
-    qemu_co_enter_next(&fst->throttled_reqs[true], NULL);
+    qemu_co_enter_next(&fst->throttled_reqs[true], QLNULL);
 }
 
 int fsdev_throttle_parse_opts(QemuOpts *opts, FsThrottle *fst, Error **errp)
@@ -100,7 +100,7 @@ void coroutine_fn fsdev_co_throttle_request(FsThrottle *fst, bool is_write,
     if (throttle_enabled(&fst->cfg)) {
         if (throttle_schedule_timer(&fst->ts, &fst->tt, is_write) ||
             !qemu_co_queue_empty(&fst->throttled_reqs[is_write])) {
-            qemu_co_queue_wait(&fst->throttled_reqs[is_write], NULL);
+            qemu_co_queue_wait(&fst->throttled_reqs[is_write], QLNULL);
         }
 
         throttle_account(&fst->ts, is_write, iov_size(iov, iovcnt));
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 45a788f..35976e2 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -2888,7 +2888,7 @@ static void coroutine_fn v9fs_flush(void *opaque)
         /*
          * Wait for pdu to complete.
          */
-        qemu_co_queue_wait(&cancel_pdu->complete, NULL);
+        qemu_co_queue_wait(&cancel_pdu->complete, QLNULL);
         if (!qemu_co_queue_next(&cancel_pdu->complete)) {
             cancel_pdu->cancelled = 0;
             pdu_free(cancel_pdu);
diff --git a/util/qemu-co-shared-resource.c b/util/qemu-co-shared-resource.c
index 1c83cd9..7423ea4 100644
--- a/util/qemu-co-shared-resource.c
+++ b/util/qemu-co-shared-resource.c
@@ -64,7 +64,7 @@ void coroutine_fn co_get_from_shres(SharedResource *s, uint64_t n)
 {
     assert(n <= s->total);
     while (!co_try_get_from_shres(s, n)) {
-        qemu_co_queue_wait(&s->queue, NULL);
+        qemu_co_queue_wait(&s->queue, QLNULL);
     }
 }
 
-- 
2.7.4