[Qemu-block] [PATCH RFC 04/16] block: Propagate BLK_PERM_AIO_CONTEXT_CHANGE down the graph

[Fam Zheng]

bdrv_set_aio_context can take care of children recursively, so it is
okay to pass down the perm.

Signed-off-by: Fam Zheng <address@hidden>
---
 block.c       | 18 ++++++++++--------
 block/vvfat.c |  2 +-
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/block.c b/block.c
index ae9327b..0190087 100644
--- a/block.c
+++ b/block.c
@@ -1670,7 +1670,8 @@ int bdrv_child_try_set_perm(BdrvChild *c, uint64_t perm, 
uint64_t shared,
 #define DEFAULT_PERM_PASSTHROUGH (BLK_PERM_CONSISTENT_READ \
                                  | BLK_PERM_WRITE \
                                  | BLK_PERM_WRITE_UNCHANGED \
-                                 | BLK_PERM_RESIZE)
+                                 | BLK_PERM_RESIZE \
+                                 | BLK_PERM_AIO_CONTEXT_CHANGE)
 #define DEFAULT_PERM_UNCHANGED (BLK_PERM_ALL & ~DEFAULT_PERM_PASSTHROUGH)
 
 void bdrv_filter_default_perms(BlockDriverState *bs, BdrvChild *c,
@@ -1713,21 +1714,22 @@ void bdrv_format_default_perms(BlockDriverState *bs, 
BdrvChild *c,
         perm |= BLK_PERM_CONSISTENT_READ;
         shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
     } else {
-        /* We want consistent read from backing files if the parent needs it.
+        /* We want consistent read and aio context change from backing files if
+         * the parent needs it.
          * No other operations are performed on backing files. */
-        perm &= BLK_PERM_CONSISTENT_READ;
+        perm &= BLK_PERM_CONSISTENT_READ | BLK_PERM_AIO_CONTEXT_CHANGE;
 
-        /* If the parent can deal with changing data, we're okay with a
+        /* If the parent can deal with changing aio context, we're okay too;
+         * If the parent can deal with changing data, we're okay with a
          * writable and resizable backing file. */
         /* TODO Require !(perm & BLK_PERM_CONSISTENT_READ), too? */
+        shared &= BLK_PERM_AIO_CONTEXT_CHANGE | BLK_PERM_WRITE;
         if (shared & BLK_PERM_WRITE) {
-            shared = BLK_PERM_WRITE | BLK_PERM_RESIZE;
-        } else {
-            shared = 0;
+            shared |= BLK_PERM_WRITE | BLK_PERM_RESIZE;
         }
 
         shared |= BLK_PERM_CONSISTENT_READ | BLK_PERM_GRAPH_MOD |
-                  BLK_PERM_WRITE_UNCHANGED;
+                  BLK_PERM_WRITE_UNCHANGED | BLK_PERM_AIO_CONTEXT_CHANGE;
     }
 
     *nperm = perm;
diff --git a/block/vvfat.c b/block/vvfat.c
index af5153d..70ce452 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -3080,7 +3080,7 @@ static void vvfat_child_perm(BlockDriverState *bs, 
BdrvChild *c,
     if (c == s->qcow) {
         /* This is a private node, nobody should try to attach to it */
         *nperm = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE;
-        *nshared = BLK_PERM_WRITE_UNCHANGED;
+        *nshared = BLK_PERM_WRITE_UNCHANGED | BLK_PERM_AIO_CONTEXT_CHANGE;
     } else {
         /* The backing file is there so 'commit' can use it. vvfat doesn't
          * access it in any way. */
-- 
2.9.3