Signed-off-by: John Snow <js...@redhat.com>
---
RFC questions:
- Does the presence of blk->quiesce_counter relieve the burden of needing
blk->public.io_limits_disabled? I could probably eliminate this counter
entirely and just spy on the root node's quiescent state at key moments
instead. I am confident I'm traipsing on delicate drain semantics.
- Should I treat the separation of a quisced BDS/BB as a drained_end request
as an analogue to how blk_insert_bs (in this patch) handles this?
Signed-off-by: John Snow <js...@redhat.com>
---
block/block-backend.c | 25 +++++++++++++++++++++++++
include/sysemu/block-backend.h | 8 ++++++++
2 files changed, 33 insertions(+)
diff --git a/block/block-backend.c b/block/block-backend.c
index 5742c09..eb85e8b 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -65,6 +65,8 @@ struct BlockBackend {
bool allow_write_beyond_eof;
NotifierList remove_bs_notifiers, insert_bs_notifiers;
+
+ int quiesce_counter;
};
typedef struct BlockBackendAIOCB {
@@ -559,6 +561,11 @@ int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs,
Error **errp)
}
bdrv_ref(bs);
+ /* The new BDS may be quiescent, we should attempt to match */
+ if (bs->quiesce_counter) {
+ blk_root_drained_begin(blk->root);
+ }
+
notifier_list_notify(&blk->insert_bs_notifiers, blk);
if (blk->public.throttle_state) {
throttle_timers_attach_aio_context(
@@ -705,6 +712,11 @@ void blk_set_dev_ops(BlockBackend *blk, const BlockDevOps
*ops,
blk->dev_ops = ops;
blk->dev_opaque = opaque;
+
+ /* Are we currently quiesced? Should we enforce this right now? */
+ if (blk->quiesce_counter && ops->drained_begin) {
+ ops->drained_begin(opaque);
+ }
}
/*
@@ -1870,9 +1882,15 @@ static void blk_root_drained_begin(BdrvChild *child)
{
BlockBackend *blk = child->opaque;
+ blk->quiesce_counter++;
+
/* Note that blk->root may not be accessible here yet if we are just
* attaching to a BlockDriverState that is drained. Use child instead. */
+ if (blk->dev_ops && blk->dev_ops->drained_begin) {
+ blk->dev_ops->drained_begin(blk->dev_opaque);
+ }
+
if (blk->public.io_limits_disabled++ == 0) {
throttle_group_restart_blk(blk);
}
@@ -1882,6 +1900,13 @@ static void blk_root_drained_end(BdrvChild *child)
{
BlockBackend *blk = child->opaque;
+ assert(blk->quiesce_counter);
+ blk->quiesce_counter--;
+
assert(blk->public.io_limits_disabled);
--blk->public.io_limits_disabled;
+
+ if (blk->dev_ops && blk->dev_ops->drained_end) {
+ blk->dev_ops->drained_end(blk->dev_opaque);
+ }
}
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 096c17f..c6f4408 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -58,6 +58,14 @@ typedef struct BlockDevOps {
* Runs when the size changed (e.g. monitor command block_resize)
*/
void (*resize_cb)(void *opaque);
+ /*
+ * Runs when the backend receives a drain request.
+ */
+ void (*drained_begin)(void *opaque);
+ /*
+ * Runs when the backend's drain request ends.
+ */
+ void (*drained_end)(void *opaque);
} BlockDevOps;
/* This struct is embedded in (the private) BlockBackend struct and contains
--
2.9.3
