[Qemu-devel] [RFC PATCH 1/7] block: Add op blocker type "device IO"

[Fam Zheng <famz@redhat.com>]

Preventing device from submitting IO is useful around various nested
poll. Op blocker is a good place to put this flag.

Devices would submit IO requests through blk_* block backend interface,
which calls blk_check_request to check the validity. Return -EBUSY if
the operation is blocked, in which case device IO is temporarily
disabled by another BDS user.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/block-backend.c | 4 ++++
 include/block/block.h | 1 +
 2 files changed, 5 insertions(+)

diff --git a/block/block-backend.c b/block/block-backend.c
index 93e46f3..71fc695 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -478,6 +478,10 @@ static int blk_check_request(BlockBackend *blk, int64_t sector_num,
         return -EIO;
     }
 
+    if (bdrv_op_is_blocked(blk->bs, BLOCK_OP_TYPE_DEVICE_IO, NULL)) {
+        return -EBUSY;
+    }
+
     return blk_check_byte_request(blk, sector_num * BDRV_SECTOR_SIZE,
                                   nb_sectors * BDRV_SECTOR_SIZE);
 }
diff --git a/include/block/block.h b/include/block/block.h
index 7d1a717..906fb31 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -159,6 +159,7 @@ typedef enum BlockOpType {
     BLOCK_OP_TYPE_RESIZE,
     BLOCK_OP_TYPE_STREAM,
     BLOCK_OP_TYPE_REPLACE,
+    BLOCK_OP_TYPE_DEVICE_IO,
     BLOCK_OP_TYPE_MAX,
 } BlockOpType;
 
-- 
1.9.3