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>

block.c

@@ -1907,7 +1907,7 @@ void bdrv_close(BlockDriverState *bs)
     }
 
     /* Disable I/O limits and drain all pending throttled requests */
-    if (bs->io_limits_enabled) {
+    if (bs->throttle_state) {
         bdrv_io_limits_disable(bs);
     }
 
@@ -3712,7 +3712,7 @@ void bdrv_detach_aio_context(BlockDriverState *bs)
         baf->detach_aio_context(baf->opaque);
     }
 
-    if (bs->io_limits_enabled) {
+    if (bs->throttle_state) {
         throttle_timers_detach_aio_context(&bs->throttle_timers);
     }
     if (bs->drv->bdrv_detach_aio_context) {
@@ -3748,7 +3748,7 @@ void bdrv_attach_aio_context(BlockDriverState *bs,
     if (bs->drv->bdrv_attach_aio_context) {
         bs->drv->bdrv_attach_aio_context(bs, new_context);
     }
-    if (bs->io_limits_enabled) {
+    if (bs->throttle_state) {
         throttle_timers_attach_aio_context(&bs->throttle_timers, new_context);
     }
 

block/qapi.c

@@ -64,7 +64,7 @@ BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs, Error **errp)
     info->backing_file_depth = bdrv_get_backing_file_depth(bs);
     info->detect_zeroes = bs->detect_zeroes;
 
-    if (bs->io_limits_enabled) {
+    if (bs->throttle_state) {
         ThrottleConfig cfg;
 
         throttle_group_get_config(bs, &cfg);

blockdev.c

@@ -2361,14 +2361,14 @@ void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
     if (throttle_enabled(&cfg)) {
         /* Enable I/O limits if they're not enabled yet, otherwise
          * just update the throttling group. */
-        if (!bs->io_limits_enabled) {
+        if (!bs->throttle_state) {
             bdrv_io_limits_enable(bs, has_group ? group : device);
         } else if (has_group) {
             bdrv_io_limits_update_group(bs, group);
         }
         /* Set the new throttling configuration */
         bdrv_set_io_limits(bs, &cfg);
-    } else if (bs->io_limits_enabled) {
+    } else if (bs->throttle_state) {
         /* If all throttling settings are set to 0, disable I/O limits */
         bdrv_io_limits_disable(bs);
     }

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.