blkcg: remove static policy ID enums

Remove BLKIO_POLICY_* enums and let blkio_policy_register() allocate
@pol->plid dynamically on registration.  The maximum number of blkcg
policies which can be registered at the same time is defined by
BLKCG_MAX_POLS constant added to include/linux/blkdev.h.

Note that blkio_policy_register() now may fail.  Policy init functions
updated accordingly and unnecessary ifdefs removed from cfq_init().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

4 files changed, 63 insertions, 40 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b1231524a097..2d4d7d6d9ae9 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -31,7 +31,7 @@ static LIST_HEAD(all_q_list);
 struct blkio_cgroup blkio_root_cgroup = { .cfq_weight = 2 * CFQ_WEIGHT_DEFAULT };
 EXPORT_SYMBOL_GPL(blkio_root_cgroup);
 
-static struct blkio_policy_type *blkio_policy[BLKIO_NR_POLICIES];
+static struct blkio_policy_type *blkio_policy[BLKCG_MAX_POLS];
 
 struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
 {
@@ -67,7 +67,7 @@ static void blkg_free(struct blkio_group *blkg)
         if (!blkg)
                 return;
 
-        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+        for (i = 0; i < BLKCG_MAX_POLS; i++) {
                 struct blkio_policy_type *pol = blkio_policy[i];
                 struct blkg_policy_data *pd = blkg->pd[i];
 
@@ -107,7 +107,7 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
         blkg->refcnt = 1;
         cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
 
-        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+        for (i = 0; i < BLKCG_MAX_POLS; i++) {
                 struct blkio_policy_type *pol = blkio_policy[i];
                 struct blkg_policy_data *pd;
 
@@ -127,7 +127,7 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
         }
 
         /* invoke per-policy init */
-        for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+        for (i = 0; i < BLKCG_MAX_POLS; i++) {
                 struct blkio_policy_type *pol = blkio_policy[i];
 
                 if (pol)
@@ -320,7 +320,7 @@ blkiocg_reset_stats(struct cgroup *cgroup, struct cftype *cftype, u64 val)
          * anyway.  If you get hit by a race, retry.
          */
         hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
-                for (i = 0; i < BLKIO_NR_POLICIES; i++) {
+                for (i = 0; i < BLKCG_MAX_POLS; i++) {
                         struct blkio_policy_type *pol = blkio_policy[i];
 
                         if (pol && pol->ops.blkio_reset_group_stats_fn)
@@ -729,46 +729,75 @@ struct cgroup_subsys blkio_subsys = {
 };
 EXPORT_SYMBOL_GPL(blkio_subsys);
 
-void blkio_policy_register(struct blkio_policy_type *blkiop)
+/**
+ * blkio_policy_register - register a blkcg policy
+ * @blkiop: blkcg policy to register
+ *
+ * Register @blkiop with blkcg core.  Might sleep and @blkiop may be
+ * modified on successful registration.  Returns 0 on success and -errno on
+ * failure.
+ */
+int blkio_policy_register(struct blkio_policy_type *blkiop)
 {
         struct request_queue *q;
+        int i, ret;
 
         mutex_lock(&blkcg_pol_mutex);
 
-        blkcg_bypass_start();
+        /* find an empty slot */
+        ret = -ENOSPC;
+        for (i = 0; i < BLKCG_MAX_POLS; i++)
+                if (!blkio_policy[i])
+                        break;
+        if (i >= BLKCG_MAX_POLS)
+                goto out_unlock;
 
-        BUG_ON(blkio_policy[blkiop->plid]);
-        blkio_policy[blkiop->plid] = blkiop;
+        /* register and update blkgs */
+        blkiop->plid = i;
+        blkio_policy[i] = blkiop;
+
+        blkcg_bypass_start();
         list_for_each_entry(q, &all_q_list, all_q_node)
                 update_root_blkg_pd(q, blkiop);
-
         blkcg_bypass_end();
 
+        /* everything is in place, add intf files for the new policy */
         if (blkiop->cftypes)
                 WARN_ON(cgroup_add_cftypes(&blkio_subsys, blkiop->cftypes));
-
+        ret = 0;
+out_unlock:
         mutex_unlock(&blkcg_pol_mutex);
+        return ret;
 }
 EXPORT_SYMBOL_GPL(blkio_policy_register);
 
+/**
+ * blkiop_policy_unregister - unregister a blkcg policy
+ * @blkiop: blkcg policy to unregister
+ *
+ * Undo blkio_policy_register(@blkiop).  Might sleep.
+ */
 void blkio_policy_unregister(struct blkio_policy_type *blkiop)
 {
         struct request_queue *q;
 
         mutex_lock(&blkcg_pol_mutex);
 
+        if (WARN_ON(blkio_policy[blkiop->plid] != blkiop))
+                goto out_unlock;
+
+        /* kill the intf files first */
         if (blkiop->cftypes)
                 cgroup_rm_cftypes(&blkio_subsys, blkiop->cftypes);
 
-        blkcg_bypass_start();
-
-        BUG_ON(blkio_policy[blkiop->plid] != blkiop);
+        /* unregister and update blkgs */
         blkio_policy[blkiop->plid] = NULL;
 
+        blkcg_bypass_start();
         list_for_each_entry(q, &all_q_list, all_q_node)
                 update_root_blkg_pd(q, blkiop);
         blkcg_bypass_end();
-
+out_unlock:
         mutex_unlock(&blkcg_pol_mutex);
 }
 EXPORT_SYMBOL_GPL(blkio_policy_unregister);
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 26949731108f..be80d6eb6531 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -17,13 +17,6 @@
 #include <linux/u64_stats_sync.h>
 #include <linux/seq_file.h>
 
-enum blkio_policy_id {
-        BLKIO_POLICY_PROP = 0,          /* Proportional Bandwidth division */
-        BLKIO_POLICY_THROTL,            /* Throttling */
-
-        BLKIO_NR_POLICIES,
-};
-
 /* Max limits for throttle policy */
 #define THROTL_IOPS_MAX         UINT_MAX
 
@@ -86,7 +79,7 @@ struct blkio_group {
         /* reference count */
         int refcnt;
 
-        struct blkg_policy_data *pd[BLKIO_NR_POLICIES];
+        struct blkg_policy_data *pd[BLKCG_MAX_POLS];
 
         struct rcu_head rcu_head;
 };
@@ -103,7 +96,7 @@ struct blkio_policy_ops {
 
 struct blkio_policy_type {
         struct blkio_policy_ops ops;
-        enum blkio_policy_id plid;
+        int plid;
         size_t pdata_size;              /* policy specific private data size */
         struct cftype *cftypes;         /* cgroup files for the policy */
 };
@@ -113,7 +106,7 @@ extern void blkcg_drain_queue(struct request_queue *q);
 extern void blkcg_exit_queue(struct request_queue *q);
 
 /* Blkio controller policy registration */
-extern void blkio_policy_register(struct blkio_policy_type *);
+extern int blkio_policy_register(struct blkio_policy_type *);
 extern void blkio_policy_unregister(struct blkio_policy_type *);
 extern void blkg_destroy_all(struct request_queue *q, bool destroy_root);
 extern void update_root_blkg_pd(struct request_queue *q,
@@ -329,7 +322,7 @@ struct blkio_policy_type {
 static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
 static inline void blkcg_drain_queue(struct request_queue *q) { }
 static inline void blkcg_exit_queue(struct request_queue *q) { }
-static inline void blkio_policy_register(struct blkio_policy_type *blkiop) { }
+static inline int blkio_policy_register(struct blkio_policy_type *blkiop) { return 0; }
 static inline void blkio_policy_unregister(struct blkio_policy_type *blkiop) { }
 static inline void blkg_destroy_all(struct request_queue *q,
                                     bool destory_root) { }
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 07c17c27a628..0dc4645aa7fe 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1089,7 +1089,6 @@ static struct blkio_policy_type blkio_policy_throtl = {
                 .blkio_exit_group_fn = throtl_exit_blkio_group,
                 .blkio_reset_group_stats_fn = throtl_reset_group_stats,
         },
-        .plid = BLKIO_POLICY_THROTL,
         .pdata_size = sizeof(struct throtl_grp),
         .cftypes = throtl_files,
 };
@@ -1271,8 +1270,7 @@ static int __init throtl_init(void)
         if (!kthrotld_workqueue)
                 panic("Failed to create kthrotld\n");
 
-        blkio_policy_register(&blkio_policy_throtl);
-        return 0;
+        return blkio_policy_register(&blkio_policy_throtl);
 }
 
 module_init(throtl_init);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index d02f0ae9637f..08db2fc70c29 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -4157,7 +4157,6 @@ static struct blkio_policy_type blkio_policy_cfq = {
                 .blkio_init_group_fn =          cfq_init_blkio_group,
                 .blkio_reset_group_stats_fn =   cfqg_stats_reset,
         },
-        .plid = BLKIO_POLICY_PROP,
         .pdata_size = sizeof(struct cfq_group),
         .cftypes = cfq_blkcg_files,
 };
@@ -4181,27 +4180,31 @@ static int __init cfq_init(void)
 #else
                 cfq_group_idle = 0;
 #endif
+
+        ret = blkio_policy_register(&blkio_policy_cfq);
+        if (ret)
+                return ret;
+
         cfq_pool = KMEM_CACHE(cfq_queue, 0);
         if (!cfq_pool)
-                return -ENOMEM;
+                goto err_pol_unreg;
 
         ret = elv_register(&iosched_cfq);
-        if (ret) {
-                kmem_cache_destroy(cfq_pool);
-                return ret;
-        }
+        if (ret)
+                goto err_free_pool;
 
-#ifdef CONFIG_CFQ_GROUP_IOSCHED
-        blkio_policy_register(&blkio_policy_cfq);
-#endif
         return 0;
+
+err_free_pool:
+        kmem_cache_destroy(cfq_pool);
+err_pol_unreg:
+        blkio_policy_unregister(&blkio_policy_cfq);
+        return ret;
 }
 
 static void __exit cfq_exit(void)
 {
-#ifdef CONFIG_CFQ_GROUP_IOSCHED
         blkio_policy_unregister(&blkio_policy_cfq);
-#endif
         elv_unregister(&iosched_cfq);
         kmem_cache_destroy(cfq_pool);
 }