block: add aio_flush operation

Instead stalling the VCPU while serving a cache flush try to do it
asynchronously.  Use our good old helper thread pool to issue an
asynchronous fdatasync for raw-posix.  Note that while Linux AIO
implements a fdatasync operation it is not useful for us because
it isn't actually implement in asynchronous fashion.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

block.c

@@ -54,6 +54,8 @@ static BlockDriverAIOCB *bdrv_aio_readv_em(BlockDriverState *bs,
 static BlockDriverAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
         BlockDriverCompletionFunc *cb, void *opaque);
+static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque);
 static int bdrv_read_em(BlockDriverState *bs, int64_t sector_num,
                         uint8_t *buf, int nb_sectors);
 static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,
@@ -138,6 +140,10 @@ void bdrv_register(BlockDriver *bdrv)
         bdrv->bdrv_read = bdrv_read_em;
         bdrv->bdrv_write = bdrv_write_em;
     }
+
+    if (!bdrv->bdrv_aio_flush)
+        bdrv->bdrv_aio_flush = bdrv_aio_flush_em;
+
     bdrv->next = first_drv;
     first_drv = bdrv;
 }
@@ -1552,6 +1558,21 @@ fail:
     return -1;
 }
 
+BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque)
+{
+    BlockDriver *drv = bs->drv;
+
+    if (!drv)
+        return NULL;
+
+    /*
+     * Note that unlike bdrv_flush the driver is reponsible for flushing a
+     * backing image if it exists.
+     */
+    return drv->bdrv_aio_flush(bs, cb, opaque);
+}
+
 void bdrv_aio_cancel(BlockDriverAIOCB *acb)
 {
     acb->pool->cancel(acb);
@@ -1642,6 +1663,25 @@ static BlockDriverAIOCB *bdrv_aio_writev_em(BlockDriverState *bs,
     return bdrv_aio_rw_vector(bs, sector_num, qiov, nb_sectors, cb, opaque, 1);
 }
 
+static BlockDriverAIOCB *bdrv_aio_flush_em(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque)
+{
+    BlockDriverAIOCBSync *acb;
+
+    acb = qemu_aio_get(&bdrv_em_aio_pool, bs, cb, opaque);
+    acb->is_write = 1; /* don't bounce in the completion hadler */
+    acb->qiov = NULL;
+    acb->bounce = NULL;
+    acb->ret = 0;
+
+    if (!acb->bh)
+        acb->bh = qemu_bh_new(bdrv_aio_bh_cb, acb);
+
+    bdrv_flush(bs);
+    qemu_bh_schedule(acb->bh);
+    return &acb->common;
+}
+
 /**************************************************************/
 /* sync block device emulation */
 

block.h

@@ -85,6 +85,8 @@ BlockDriverAIOCB *bdrv_aio_readv(BlockDriverState *bs, int64_t sector_num,
 BlockDriverAIOCB *bdrv_aio_writev(BlockDriverState *bs, int64_t sector_num,
                                   QEMUIOVector *iov, int nb_sectors,
                                   BlockDriverCompletionFunc *cb, void *opaque);
+BlockDriverAIOCB *bdrv_aio_flush(BlockDriverState *bs,
+				 BlockDriverCompletionFunc *cb, void *opaque);
 void bdrv_aio_cancel(BlockDriverAIOCB *acb);
 
 typedef struct BlockRequest {

block/raw-posix-aio.h

@@ -17,8 +17,9 @@
 #define QEMU_AIO_READ         0x0001
 #define QEMU_AIO_WRITE        0x0002
 #define QEMU_AIO_IOCTL        0x0004
+#define QEMU_AIO_FLUSH        0x0008
 #define QEMU_AIO_TYPE_MASK \
-	(QEMU_AIO_READ|QEMU_AIO_WRITE|QEMU_AIO_IOCTL)
+	(QEMU_AIO_READ|QEMU_AIO_WRITE|QEMU_AIO_IOCTL|QEMU_AIO_FLUSH)
 
 /* AIO flags */
 #define QEMU_AIO_MISALIGNED   0x1000

block/raw-posix.c

@@ -574,6 +574,18 @@ static BlockDriverAIOCB *raw_aio_writev(BlockDriverState *bs,
                           cb, opaque, QEMU_AIO_WRITE);
 }
 
+static BlockDriverAIOCB *raw_aio_flush(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque)
+{
+    BDRVRawState *s = bs->opaque;
+
+    if (fd_open(bs) < 0)
+        return NULL;
+
+    return paio_submit(bs, s->aio_ctx, s->fd, 0, NULL, 0,
+    		       cb, opaque, QEMU_AIO_FLUSH);
+}
+
 static void raw_close(BlockDriverState *bs)
 {
     BDRVRawState *s = bs->opaque;
@@ -749,6 +761,7 @@ static BlockDriver bdrv_raw = {
 
     .bdrv_aio_readv = raw_aio_readv,
     .bdrv_aio_writev = raw_aio_writev,
+    .bdrv_aio_flush = raw_aio_flush,
 
     .bdrv_truncate = raw_truncate,
     .bdrv_getlength = raw_getlength,
@@ -1002,6 +1015,7 @@ static BlockDriver bdrv_host_device = {
 
     .bdrv_aio_readv	= raw_aio_readv,
     .bdrv_aio_writev	= raw_aio_writev,
+    .bdrv_aio_flush	= raw_aio_flush,
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
@@ -1096,6 +1110,7 @@ static BlockDriver bdrv_host_floppy = {
 
     .bdrv_aio_readv     = raw_aio_readv,
     .bdrv_aio_writev    = raw_aio_writev,
+    .bdrv_aio_flush	= raw_aio_flush,
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
@@ -1176,6 +1191,7 @@ static BlockDriver bdrv_host_cdrom = {
 
     .bdrv_aio_readv     = raw_aio_readv,
     .bdrv_aio_writev    = raw_aio_writev,
+    .bdrv_aio_flush	= raw_aio_flush,
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,
@@ -1295,6 +1311,7 @@ static BlockDriver bdrv_host_cdrom = {
 
     .bdrv_aio_readv     = raw_aio_readv,
     .bdrv_aio_writev    = raw_aio_writev,
+    .bdrv_aio_flush	= raw_aio_flush,
 
     .bdrv_read          = raw_read,
     .bdrv_write         = raw_write,

block_int.h

@@ -69,6 +69,8 @@ struct BlockDriver {
     BlockDriverAIOCB *(*bdrv_aio_writev)(BlockDriverState *bs,
         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
         BlockDriverCompletionFunc *cb, void *opaque);
+    BlockDriverAIOCB *(*bdrv_aio_flush)(BlockDriverState *bs,
+        BlockDriverCompletionFunc *cb, void *opaque);
 
     int (*bdrv_aio_multiwrite)(BlockDriverState *bs, BlockRequest *reqs,
         int num_reqs);

posix-aio-compat.c

@@ -134,6 +134,16 @@ static size_t handle_aiocb_ioctl(struct qemu_paiocb *aiocb)
 	return aiocb->aio_nbytes;
 }
 
+static size_t handle_aiocb_flush(struct qemu_paiocb *aiocb)
+{
+    int ret;
+
+    ret = fdatasync(aiocb->aio_fildes);
+    if (ret == -1)
+        return -errno;
+    return 0;
+}
+
 #ifdef CONFIG_PREADV
 
 static ssize_t
@@ -330,6 +340,9 @@ static void *aio_thread(void *unused)
         case QEMU_AIO_WRITE:
 		ret = handle_aiocb_rw(aiocb);
 		break;
+        case QEMU_AIO_FLUSH:
+                ret = handle_aiocb_flush(aiocb);
+                break;
         case QEMU_AIO_IOCTL:
 		ret = handle_aiocb_ioctl(aiocb);
 		break;
@@ -530,8 +543,10 @@ BlockDriverAIOCB *paio_submit(BlockDriverState *bs, void *aio_ctx, int fd,
     acb->aio_type = type;
     acb->aio_fildes = fd;
     acb->ev_signo = SIGUSR2;
-    acb->aio_iov = qiov->iov;
-    acb->aio_niov = qiov->niov;
+    if (qiov) {
+        acb->aio_iov = qiov->iov;
+        acb->aio_niov = qiov->niov;
+    }
     acb->aio_nbytes = nb_sectors * 512;
     acb->aio_offset = sector_num * 512;