block: introduce BDRV_POLL_WHILE

We want the BDS event loop to run exclusively in the iothread that
owns the BDS's AioContext.  This macro will provide the synchronization
between the two event loops; for now it just wraps the common idiom
of a while loop around aio_poll.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-Id: <1477565348-5458-8-git-send-email-pbonzini@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>

block/block-backend.c

@@ -878,7 +878,6 @@ static int blk_prw(BlockBackend *blk, int64_t offset, uint8_t *buf,
                    int64_t bytes, CoroutineEntry co_entry,
                    BdrvRequestFlags flags)
 {
-    AioContext *aio_context;
     QEMUIOVector qiov;
     struct iovec iov;
     Coroutine *co;
@@ -900,11 +899,7 @@ static int blk_prw(BlockBackend *blk, int64_t offset, uint8_t *buf,
 
     co = qemu_coroutine_create(co_entry, &rwco);
     qemu_coroutine_enter(co);
-
+    BDRV_POLL_WHILE(blk_bs(blk), rwco.ret == NOT_DONE);
-    aio_context = blk_get_aio_context(blk);
-    while (rwco.ret == NOT_DONE) {
-        aio_poll(aio_context, true);
-    }
 
     return rwco.ret;
 }

block/io.c

@@ -156,23 +156,12 @@ bool bdrv_requests_pending(BlockDriverState *bs)
     return false;
 }
 
-static bool bdrv_drain_poll(BlockDriverState *bs)
-{
-    bool waited = false;
-
-    while (atomic_read(&bs->in_flight) > 0) {
-        aio_poll(bdrv_get_aio_context(bs), true);
-        waited = true;
-    }
-    return waited;
-}
-
 static bool bdrv_drain_recurse(BlockDriverState *bs)
 {
     BdrvChild *child;
     bool waited;
 
-    waited = bdrv_drain_poll(bs);
+    waited = BDRV_POLL_WHILE(bs, atomic_read(&bs->in_flight) > 0);
 
     if (bs->drv && bs->drv->bdrv_drain) {
         bs->drv->bdrv_drain(bs);
@@ -597,13 +586,9 @@ static int bdrv_prwv_co(BdrvChild *child, int64_t offset,
         /* Fast-path if already in coroutine context */
         bdrv_rw_co_entry(&rwco);
     } else {
-        AioContext *aio_context = bdrv_get_aio_context(child->bs);
-
         co = qemu_coroutine_create(bdrv_rw_co_entry, &rwco);
         qemu_coroutine_enter(co);
-        while (rwco.ret == NOT_DONE) {
+        BDRV_POLL_WHILE(child->bs, rwco.ret == NOT_DONE);
-            aio_poll(aio_context, true);
-        }
     }
     return rwco.ret;
 }
@@ -1845,14 +1830,10 @@ int64_t bdrv_get_block_status_above(BlockDriverState *bs,
         /* Fast-path if already in coroutine context */
         bdrv_get_block_status_above_co_entry(&data);
     } else {
-        AioContext *aio_context = bdrv_get_aio_context(bs);
-
         co = qemu_coroutine_create(bdrv_get_block_status_above_co_entry,
                                    &data);
         qemu_coroutine_enter(co);
-        while (!data.done) {
+        BDRV_POLL_WHILE(bs, !data.done);
-            aio_poll(aio_context, true);
-        }
     }
     return data.ret;
 }
@@ -2379,13 +2360,9 @@ int bdrv_flush(BlockDriverState *bs)
         /* Fast-path if already in coroutine context */
         bdrv_flush_co_entry(&flush_co);
     } else {
-        AioContext *aio_context = bdrv_get_aio_context(bs);
-
         co = qemu_coroutine_create(bdrv_flush_co_entry, &flush_co);
         qemu_coroutine_enter(co);
-        while (flush_co.ret == NOT_DONE) {
+        BDRV_POLL_WHILE(bs, flush_co.ret == NOT_DONE);
-            aio_poll(aio_context, true);
-        }
     }
 
     return flush_co.ret;
@@ -2511,13 +2488,9 @@ int bdrv_pdiscard(BlockDriverState *bs, int64_t offset, int count)
         /* Fast-path if already in coroutine context */
         bdrv_pdiscard_co_entry(&rwco);
     } else {
-        AioContext *aio_context = bdrv_get_aio_context(bs);
-
         co = qemu_coroutine_create(bdrv_pdiscard_co_entry, &rwco);
         qemu_coroutine_enter(co);
-        while (rwco.ret == NOT_DONE) {
+        BDRV_POLL_WHILE(bs, rwco.ret == NOT_DONE);
-            aio_poll(aio_context, true);
-        }
     }
 
     return rwco.ret;

block/qed-table.c

@@ -174,9 +174,7 @@ int qed_read_l1_table_sync(BDRVQEDState *s)
 
     qed_read_table(s, s->header.l1_table_offset,
                    s->l1_table, qed_sync_cb, &ret);
-    while (ret == -EINPROGRESS) {
+    BDRV_POLL_WHILE(s->bs, ret == -EINPROGRESS);
-        aio_poll(bdrv_get_aio_context(s->bs), true);
-    }
 
     return ret;
 }
@@ -195,9 +193,7 @@ int qed_write_l1_table_sync(BDRVQEDState *s, unsigned int index,
     int ret = -EINPROGRESS;
 
     qed_write_l1_table(s, index, n, qed_sync_cb, &ret);
-    while (ret == -EINPROGRESS) {
+    BDRV_POLL_WHILE(s->bs, ret == -EINPROGRESS);
-        aio_poll(bdrv_get_aio_context(s->bs), true);
-    }
 
     return ret;
 }
@@ -268,9 +264,7 @@ int qed_read_l2_table_sync(BDRVQEDState *s, QEDRequest *request, uint64_t offset
     int ret = -EINPROGRESS;
 
     qed_read_l2_table(s, request, offset, qed_sync_cb, &ret);
-    while (ret == -EINPROGRESS) {
+    BDRV_POLL_WHILE(s->bs, ret == -EINPROGRESS);
-        aio_poll(bdrv_get_aio_context(s->bs), true);
-    }
 
     return ret;
 }
@@ -290,9 +284,7 @@ int qed_write_l2_table_sync(BDRVQEDState *s, QEDRequest *request,
     int ret = -EINPROGRESS;
 
     qed_write_l2_table(s, request, index, n, flush, qed_sync_cb, &ret);
-    while (ret == -EINPROGRESS) {
+    BDRV_POLL_WHILE(s->bs, ret == -EINPROGRESS);
-        aio_poll(bdrv_get_aio_context(s->bs), true);
-    }
 
     return ret;
 }

include/block/block.h

@@ -334,6 +334,15 @@ void bdrv_drain(BlockDriverState *bs);
 void coroutine_fn bdrv_co_drain(BlockDriverState *bs);
 void bdrv_drain_all(void);
 
+#define BDRV_POLL_WHILE(bs, cond) ({                       \
+    bool waited_ = false;                                  \
+    BlockDriverState *bs_ = (bs);                          \
+    while ((cond)) {                                       \
+        aio_poll(bdrv_get_aio_context(bs_), true);         \
+        waited_ = true;                                    \
+    }                                                      \
+    waited_; })
+
 int bdrv_pdiscard(BlockDriverState *bs, int64_t offset, int count);
 int bdrv_co_pdiscard(BlockDriverState *bs, int64_t offset, int count);
 int bdrv_has_zero_init_1(BlockDriverState *bs);