[Qemu-devel] [RFC] block: Removed coroutine ownership assumption

[Peter A. G. Crosthwaite]

The block layer assumes that it is the only user of coroutines -
The qemu_in_coroutine() is used to determine if a function is in one of the
block layers coroutines, which is flawed. I.E. If a client (e.g. a device or
a machine model) of the block layer uses couroutine itself, the block layer
will identify the callers coroutines as its own, and may falsely yield the
calling coroutine (instead of creating its own to yield).

AFAICT, there are no conflicts in the QEMU master here yet, but its kind of an
issue, as anyone who comes along and used coroutines and the block layer
together is going to run into some very obscure and hard to debug race
conditions.

Signed-off-by: Peter A. G. Crosthwaite <address@hidden>
---
 block.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/block.c b/block.c
index 0acdcac..b50af15 100644
--- a/block.c
+++ b/block.c
@@ -380,7 +380,7 @@ int bdrv_create(BlockDriver *drv, const char* filename,
         return -ENOTSUP;
     }
 
-    if (qemu_in_coroutine()) {
+    if (0) {
         /* Fast-path if already in coroutine context */
         bdrv_create_co_entry(&cco);
     } else {
@@ -1590,7 +1590,7 @@ static int bdrv_rw_co(BlockDriverState *bs, int64_t 
sector_num, uint8_t *buf,
         bdrv_io_limits_disable(bs);
     }
 
-    if (qemu_in_coroutine()) {
+    if (0) {
         /* Fast-path if already in coroutine context */
         bdrv_rw_co_entry(&rwco);
     } else {
@@ -3813,7 +3813,7 @@ int bdrv_flush(BlockDriverState *bs)
         .ret = NOT_DONE,
     };
 
-    if (qemu_in_coroutine()) {
+    if (0) {
         /* Fast-path if already in coroutine context */
         bdrv_flush_co_entry(&rwco);
     } else {
@@ -3874,7 +3874,7 @@ int bdrv_discard(BlockDriverState *bs, int64_t 
sector_num, int nb_sectors)
         .ret = NOT_DONE,
     };
 
-    if (qemu_in_coroutine()) {
+    if (0) {
         /* Fast-path if already in coroutine context */
         bdrv_discard_co_entry(&rwco);
     } else {
-- 
1.7.3.2