throttle: Use bs->throttle_state instead of bs->io_limits_enabled

There are two ways to check for I/O limits in a BlockDriverState:

- bs->throttle_state: if this pointer is not NULL, it means that this
  BDS is member of a throttling group, its ThrottleTimers structure
  has been initialized and its I/O limits are ready to be applied.

- bs->io_limits_enabled: if true it means that the throttle_state
  pointer is valid _and_ the limits are currently enabled.

The latter is used in several places to check whether a BDS has I/O
limits configured, but what it really checks is whether requests
are being throttled or not. For example, io_limits_enabled can be
temporarily set to false in cases like bdrv_read_unthrottled() without
otherwise touching the throtting configuration of that BDS.

This patch replaces bs->io_limits_enabled with bs->throttle_state in
all cases where what we really want to check is the existence of I/O
limits, not whether they are currently enabled or not.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 6a3f64d..603145a 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -390,7 +390,10 @@ struct BlockDriverState {
     /* number of in-flight serialising requests */
     unsigned int serialising_in_flight;
 
-    /* I/O throttling */
+    /* I/O throttling.
+     * throttle_state tells us if this BDS has I/O limits configured.
+     * io_limits_enabled tells us if they are currently being
+     * enforced, but it can be temporarily set to false */
     CoQueue      throttled_reqs[2];
     bool         io_limits_enabled;
     /* The following fields are protected by the ThrottleGroup lock.