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>

1 files changed, 44 insertions, 15 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);