Re: [Qemu-block] [PATCH v9 5/6] block: add throttle block filter driver

[Stefan Hajnoczi]

On Fri, Aug 25, 2017 at 04:20:27PM +0300, Manos Pitsidianakis wrote:
> +static int throttle_configure_tgm(BlockDriverState *bs,
> +  ThrottleGroupMember *tgm,
> +  QDict *options, Error **errp)
> +{
> +int ret;
> +const char *group_name;
> +Error *local_err = NULL;
> +QemuOpts *opts = qemu_opts_create(_opts, NULL, 0, _abort);
> +
> +qemu_opts_absorb_qdict(opts, options, _err);
> +if (local_err) {
> +error_propagate(errp, local_err);
> +ret = -EINVAL;
> +goto fin;
> +}
> +
> +group_name = qemu_opt_get(opts, QEMU_OPT_THROTTLE_GROUP_NAME);
> +if (!group_name) {
> +error_setg(errp, "Please specify a throttle group.");

error_setg() messages do not end with punctuation:

  error_setg(errp, "Please specify a throttle group");

This is not worth respinning for though.

> +ret = -EINVAL;
> +goto fin;
> +} else if (!throttle_group_exists(group_name)) {
> +error_setg(errp, "Throttle group '%s' does not exist.", group_name);

Same here.

Anyway:

Reviewed-by: Stefan Hajnoczi 

[Qemu-block] [PATCH v9 5/6] block: add throttle block filter driver

[Manos Pitsidianakis]

block/throttle.c uses existing I/O throttle infrastructure inside a
block filter driver. I/O operations are intercepted in the filter's
read/write coroutines, and referred to block/throttle-groups.c

The driver can be used with the syntax
-drive driver=throttle,file.filename=foo.qcow2,throttle-group=bar

which registers the throttle filter node with the ThrottleGroup 'bar'. The
given group must be created beforehand with object-add or -object.

Reviewed-by: Alberto Garcia 
Signed-off-by: Manos Pitsidianakis 
---
 qapi/block-core.json|  18 ++-
 include/block/throttle-groups.h |   5 +
 include/qemu/throttle-options.h |   1 +
 block/throttle-groups.c |  15 ++-
 block/throttle.c| 250 
 block/Makefile.objs |   1 +
 6 files changed, 288 insertions(+), 2 deletions(-)
 create mode 100644 block/throttle.c

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 0bdc69aa5f..03724146a4 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -,6 +,7 @@
 # Drivers that are supported in block device operations.
 #
 # @vxhs: Since 2.10
+# @throttle: Since 2.11
 #
 # Since: 2.9
 ##
@@ -2231,7 +2232,7 @@
 'host_device', 'http', 'https', 'iscsi', 'luks', 'nbd', 'nfs',
 'null-aio', 'null-co', 'parallels', 'qcow', 'qcow2', 'qed',
 'quorum', 'raw', 'rbd', 'replication', 'sheepdog', 'ssh',
-'vdi', 'vhdx', 'vmdk', 'vpc', 'vvfat', 'vxhs' ] }
+'throttle', 'vdi', 'vhdx', 'vmdk', 'vpc', 'vvfat', 'vxhs' ] }
 
 ##
 # @BlockdevOptionsFile:
@@ -3095,6 +3096,20 @@
 '*tls-creds': 'str' } }
 
 ##
+# @BlockdevOptionsThrottle:
+#
+# Driver specific block device options for the throttle driver
+#
+# @throttle-group:   the name of the throttle-group object to use. It
+#must already exist.
+# @file: reference to or definition of the data source block device
+# Since: 2.11
+##
+{ 'struct': 'BlockdevOptionsThrottle',
+  'data': { 'throttle-group': 'str',
+'file' : 'BlockdevRef'
+ } }
+##
 # @BlockdevOptions:
 #
 # Options for creating a block device.  Many options are available for all
@@ -3155,6 +3170,7 @@
   'replication':'BlockdevOptionsReplication',
   'sheepdog':   'BlockdevOptionsSheepdog',
   'ssh':'BlockdevOptionsSsh',
+  'throttle':   'BlockdevOptionsThrottle',
   'vdi':'BlockdevOptionsGenericFormat',
   'vhdx':   'BlockdevOptionsGenericFormat',
   'vmdk':   'BlockdevOptionsGenericCOWFormat',
diff --git a/include/block/throttle-groups.h b/include/block/throttle-groups.h
index 82f030523f..e2fd0513c4 100644
--- a/include/block/throttle-groups.h
+++ b/include/block/throttle-groups.h
@@ -76,5 +76,10 @@ void coroutine_fn 
throttle_group_co_io_limits_intercept(ThrottleGroupMember *tgm
 void throttle_group_attach_aio_context(ThrottleGroupMember *tgm,
AioContext *new_context);
 void throttle_group_detach_aio_context(ThrottleGroupMember *tgm);
+/*
+ * throttle_group_exists() must be called under the global
+ * mutex.
+ */
+bool throttle_group_exists(const char *name);
 
 #endif
diff --git a/include/qemu/throttle-options.h b/include/qemu/throttle-options.h
index 182b7896e1..3528a8f4a2 100644
--- a/include/qemu/throttle-options.h
+++ b/include/qemu/throttle-options.h
@@ -29,6 +29,7 @@
 #define QEMU_OPT_BPS_WRITE_MAX "bps-write-max"
 #define QEMU_OPT_BPS_WRITE_MAX_LENGTH "bps-write-max-length"
 #define QEMU_OPT_IOPS_SIZE "iops-size"
+#define QEMU_OPT_THROTTLE_GROUP_NAME "throttle-group"
 
 #define THROTTLE_OPT_PREFIX "throttling."
 #define THROTTLE_OPTS \
diff --git a/block/throttle-groups.c b/block/throttle-groups.c
index 5993575838..454bfcb067 100644
--- a/block/throttle-groups.c
+++ b/block/throttle-groups.c
@@ -101,6 +101,14 @@ static ThrottleGroup *throttle_group_by_name(const char 
*name)
 return NULL;
 }
 
+/* This function reads throttle_groups and must be called under the global
+ * mutex.
+ */
+bool throttle_group_exists(const char *name)
+{
+return throttle_group_by_name(name) != NULL;
+}
+
 /* Increments the reference count of a ThrottleGroup given its name.
  *
  * If no ThrottleGroup is found with the given name a new one is
@@ -543,6 +551,11 @@ void throttle_group_unregister_tgm(ThrottleGroupMember 
*tgm)
 ThrottleGroupMember *token;
 int i;
 
+if (!ts) {
+/* Discard already unregistered tgm */
+return;
+}
+
 assert(tgm->pending_reqs[0] == 0 && tgm->pending_reqs[1] == 0);
 assert(qemu_co_queue_empty(>throttled_reqs[0]));
 assert(qemu_co_queue_empty(>throttled_reqs[1]));
@@ -709,7 +722,7 @@ static void throttle_group_obj_complete(UserCreatable *obj, 
Error **errp)
 assert(tg->name);
 
 /* error if name is duplicate */
-if (throttle_group_by_name(tg->name) != NULL) {
+if (throttle_group_exists(tg->name))