disk/aio: Fix use of disk->async

Add an 'async' attribute to disk_image_operations, that describes if they
can submit async I/O or not. disk_image->async is now set iff
CONFIG_HAS_AIO and the ops do use AIO.

This fixes qcow1, which used to set async = 1 even though the qcow
operations don't use AIO. The disk core would perform the read/write
operation without pushing the completion onto the virtio queue, and the
guest would be stuck waiting.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

5 files changed, 15 insertions, 21 deletions

diff --git a/disk/aio.c b/disk/aio.c
index 6afcffe5..007415c6 100644
--- a/disk/aio.c
+++ b/disk/aio.c
@@ -90,6 +90,10 @@ int disk_aio_setup(struct disk_image *disk)
 	int r;
 	pthread_t thread;
 
+	/* No need to setup AIO if the disk ops won't make use of it */
+	if (!disk->ops->async)
+		return 0;
+
 	disk->evt = eventfd(0, 0);
 	if (disk->evt < 0)
 		return -errno;
@@ -101,11 +105,16 @@ int disk_aio_setup(struct disk_image *disk)
 		close(disk->evt);
 		return r;
 	}
+
+	disk->async = true;
 	return 0;
 }
 
 void disk_aio_destroy(struct disk_image *disk)
 {
+	if (!disk->async)
+		return;
+
 	close(disk->evt);
 	io_destroy(disk->ctx);
 }
diff --git a/disk/blk.c b/disk/blk.c
index 37581d33..48922e02 100644
--- a/disk/blk.c
+++ b/disk/blk.c
@@ -9,6 +9,7 @@
 static struct disk_image_operations blk_dev_ops = {
 	.read	= raw_image__read,
 	.write	= raw_image__write,
+	.async	= true,
 };
 
 static bool is_mounted(struct stat *st)
@@ -35,7 +36,6 @@ static bool is_mounted(struct stat *st)
 
 struct disk_image *blkdev__probe(const char *filename, int flags, struct stat *st)
 {
-	struct disk_image *disk;
 	int fd, r;
 	u64 size;
 
@@ -67,10 +67,5 @@ struct disk_image *blkdev__probe(const char *filename, int flags, struct stat *s
 	 * mmap large disk. There is not enough virtual address space
 	 * in 32-bit host. However, this works on 64-bit host.
 	 */
-	disk = disk_image__new(fd, size, &blk_dev_ops, DISK_IMAGE_REGULAR);
-#ifdef CONFIG_HAS_AIO
-		if (!IS_ERR_OR_NULL(disk))
-			disk->async = 1;
-#endif
-	return disk;
+	return disk_image__new(fd, size, &blk_dev_ops, DISK_IMAGE_REGULAR);
 }
diff --git a/disk/qcow.c b/disk/qcow.c
index bed70c65..dd6be62e 100644
--- a/disk/qcow.c
+++ b/disk/qcow.c
@@ -1337,7 +1337,6 @@ static struct disk_image *qcow2_probe(int fd, bool readonly)
 	if (IS_ERR_OR_NULL(disk_image))
 		goto free_refcount_table;
 
-	disk_image->async = 0;
 	disk_image->priv = q;
 
 	return disk_image;
@@ -1474,7 +1473,6 @@ static struct disk_image *qcow1_probe(int fd, bool readonly)
 	if (!disk_image)
 		goto free_l1_table;
 
-	disk_image->async = 1;
 	disk_image->priv = q;
 
 	return disk_image;
diff --git a/disk/raw.c b/disk/raw.c
index 09da7e08..e869d6cc 100644
--- a/disk/raw.c
+++ b/disk/raw.c
@@ -67,6 +67,7 @@ int raw_image__close(struct disk_image *disk)
 static struct disk_image_operations raw_image_regular_ops = {
 	.read	= raw_image__read,
 	.write	= raw_image__write,
+	.async	= true,
 };
 
 struct disk_image_operations ro_ops = {
@@ -77,12 +78,11 @@ struct disk_image_operations ro_ops = {
 
 struct disk_image_operations ro_ops_nowrite = {
 	.read	= raw_image__read,
+	.async	= true,
 };
 
 struct disk_image *raw_image__probe(int fd, struct stat *st, bool readonly)
 {
-	struct disk_image *disk;
-
 	if (readonly) {
 		/*
 		 * Use mmap's MAP_PRIVATE to implement non-persistent write
@@ -93,10 +93,6 @@ struct disk_image *raw_image__probe(int fd, struct stat *st, bool readonly)
 		disk = disk_image__new(fd, st->st_size, &ro_ops, DISK_IMAGE_MMAP);
 		if (IS_ERR_OR_NULL(disk)) {
 			disk = disk_image__new(fd, st->st_size, &ro_ops_nowrite, DISK_IMAGE_REGULAR);
-#ifdef CONFIG_HAS_AIO
-			if (!IS_ERR_OR_NULL(disk))
-				disk->async = 1;
-#endif
 		}
 
 		return disk;
@@ -104,11 +100,6 @@ struct disk_image *raw_image__probe(int fd, struct stat *st, bool readonly)
 		/*
 		 * Use read/write instead of mmap
 		 */
-		disk = disk_image__new(fd, st->st_size, &raw_image_regular_ops, DISK_IMAGE_REGULAR);
-#ifdef CONFIG_HAS_AIO
-		if (!IS_ERR_OR_NULL(disk))
-			disk->async = 1;
-#endif
-		return disk;
+		return disk_image__new(fd, st->st_size, &raw_image_regular_ops, DISK_IMAGE_REGULAR);
 	}
 }
diff --git a/include/kvm/disk-image.h b/include/kvm/disk-image.h
index 953beb2d..adc9fe46 100644
--- a/include/kvm/disk-image.h
+++ b/include/kvm/disk-image.h
@@ -42,6 +42,7 @@ struct disk_image_operations {
 			int iovcount, void *param);
 	int (*flush)(struct disk_image *disk);
 	int (*close)(struct disk_image *disk);
+	bool async;
 };
 
 struct disk_image_params {