[PATCH v2 3/6] block/blkio: convert to blk_io_plug_call() API

[Stefan Hajnoczi <stefanha@redhat.com>]

Stop using the .bdrv_co_io_plug() API because it is not multi-queue
block layer friendly. Use the new blk_io_plug_call() API to batch I/O
submission instead.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
v2
- Add missing #include and fix blkio_unplug_fn() prototype [Stefano]
---
 block/blkio.c | 43 ++++++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/block/blkio.c b/block/blkio.c
index 0cdc99a729..93c6d20d39 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -17,6 +17,7 @@
 #include "qemu/error-report.h"
 #include "qapi/qmp/qdict.h"
 #include "qemu/module.h"
+#include "sysemu/block-backend.h"
 #include "exec/memory.h" /* for ram_block_discard_disable() */
 
 #include "block/block-io.h"
@@ -325,16 +326,30 @@ static void blkio_detach_aio_context(BlockDriverState *bs)
                        false, NULL, NULL, NULL, NULL, NULL);
 }
 
-/* Call with s->blkio_lock held to submit I/O after enqueuing a new request */
-static void blkio_submit_io(BlockDriverState *bs)
+/*
+ * Called by blk_io_unplug() or immediately if not plugged. Called without
+ * blkio_lock.
+ */
+static void blkio_unplug_fn(void *opaque)
 {
-    if (qatomic_read(&bs->io_plugged) == 0) {
-        BDRVBlkioState *s = bs->opaque;
+    BDRVBlkioState *s = opaque;
 
+    WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         blkioq_do_io(s->blkioq, NULL, 0, 0, NULL);
     }
 }
 
+/*
+ * Schedule I/O submission after enqueuing a new request. Called without
+ * blkio_lock.
+ */
+static void blkio_submit_io(BlockDriverState *bs)
+{
+    BDRVBlkioState *s = bs->opaque;
+
+    blk_io_plug_call(blkio_unplug_fn, s);
+}
+
 static int coroutine_fn
 blkio_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
 {
@@ -345,9 +360,9 @@ blkio_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
 
     WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         blkioq_discard(s->blkioq, offset, bytes, &cod, 0);
-        blkio_submit_io(bs);
     }
 
+    blkio_submit_io(bs);
     qemu_coroutine_yield();
     return cod.ret;
 }
@@ -378,9 +393,9 @@ blkio_co_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
 
     WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         blkioq_readv(s->blkioq, offset, iov, iovcnt, &cod, 0);
-        blkio_submit_io(bs);
     }
 
+    blkio_submit_io(bs);
     qemu_coroutine_yield();
 
     if (use_bounce_buffer) {
@@ -423,9 +438,9 @@ static int coroutine_fn blkio_co_pwritev(BlockDriverState *bs, int64_t offset,
 
     WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         blkioq_writev(s->blkioq, offset, iov, iovcnt, &cod, blkio_flags);
-        blkio_submit_io(bs);
     }
 
+    blkio_submit_io(bs);
     qemu_coroutine_yield();
 
     if (use_bounce_buffer) {
@@ -444,9 +459,9 @@ static int coroutine_fn blkio_co_flush(BlockDriverState *bs)
 
     WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         blkioq_flush(s->blkioq, &cod, 0);
-        blkio_submit_io(bs);
     }
 
+    blkio_submit_io(bs);
     qemu_coroutine_yield();
     return cod.ret;
 }
@@ -472,22 +487,13 @@ static int coroutine_fn blkio_co_pwrite_zeroes(BlockDriverState *bs,
 
     WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
         blkioq_write_zeroes(s->blkioq, offset, bytes, &cod, blkio_flags);
-        blkio_submit_io(bs);
     }
 
+    blkio_submit_io(bs);
     qemu_coroutine_yield();
     return cod.ret;
 }
 
-static void coroutine_fn blkio_co_io_unplug(BlockDriverState *bs)
-{
-    BDRVBlkioState *s = bs->opaque;
-
-    WITH_QEMU_LOCK_GUARD(&s->blkio_lock) {
-        blkio_submit_io(bs);
-    }
-}
-
 typedef enum {
     BMRR_OK,
     BMRR_SKIP,
@@ -1009,7 +1015,6 @@ static void blkio_refresh_limits(BlockDriverState *bs, Error **errp)
         .bdrv_co_pwritev         = blkio_co_pwritev, \
         .bdrv_co_flush_to_disk   = blkio_co_flush, \
         .bdrv_co_pwrite_zeroes   = blkio_co_pwrite_zeroes, \
-        .bdrv_co_io_unplug       = blkio_co_io_unplug, \
         .bdrv_refresh_limits     = blkio_refresh_limits, \
         .bdrv_register_buf       = blkio_register_buf, \
         .bdrv_unregister_buf     = blkio_unregister_buf, \
-- 
2.40.1