blkcg: move body parsing from blkg_conf_prep() to its callers

Currently, blkg_conf_prep() expects input to be of the following form

 MAJ:MIN NUM

and reads the NUM part into blkg_conf_ctx->v.  This is quite
restrictive and gets in the way in implementing blkcg interface for
the unified hierarchy.  This patch updates blkg_conf_prep() so that it
expects

 MAJ:MIN BODY_STR

where BODY_STR is an arbitrary string.  blkg_conf_ctx->v is replaced
with ->body which is a char pointer pointing to the start of BODY_STR.
Parsing of the body is moved to blkg_conf_prep()'s callers.

To allow using, for example, strsep() on blkg_conf_ctx->val, it is a
non-const pointer and to accommodate that const is dropped from @input
too.

This doesn't cause any behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-cgroup.c

@@ -24,6 +24,7 @@
 #include <linux/genhd.h>
 #include <linux/delay.h>
 #include <linux/atomic.h>
+#include <linux/ctype.h>
 #include <linux/blk-cgroup.h>
 #include "blk.h"
 
@@ -773,23 +774,28 @@ EXPORT_SYMBOL_GPL(blkg_rwstat_recursive_sum);
  * @ctx: blkg_conf_ctx to be filled
  *
  * Parse per-blkg config update from @input and initialize @ctx with the
- * result.  @ctx->blkg points to the blkg to be updated and @ctx->v the new
- * value.  This function returns with RCU read lock and queue lock held and
- * must be paired with blkg_conf_finish().
+ * result.  @ctx->blkg points to the blkg to be updated and @ctx->body the
+ * part of @input following MAJ:MIN.  This function returns with RCU read
+ * lock and queue lock held and must be paired with blkg_conf_finish().
  */
 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
-		   const char *input, struct blkg_conf_ctx *ctx)
+		   char *input, struct blkg_conf_ctx *ctx)
 	__acquires(rcu) __acquires(disk->queue->queue_lock)
 {
 	struct gendisk *disk;
 	struct blkcg_gq *blkg;
 	unsigned int major, minor;
-	unsigned long long v;
-	int part, ret;
+	int key_len, part, ret;
+	char *body;
 
-	if (sscanf(input, "%u:%u %llu", &major, &minor, &v) != 3)
+	if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
 		return -EINVAL;
 
+	body = input + key_len;
+	if (!isspace(*body))
+		return -EINVAL;
+	body = skip_spaces(body);
+
 	disk = get_gendisk(MKDEV(major, minor), &part);
 	if (!disk)
 		return -ENODEV;
@@ -826,7 +832,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 
 	ctx->disk = disk;
 	ctx->blkg = blkg;
-	ctx->v = v;
+	ctx->body = body;
 	return 0;
 }
 EXPORT_SYMBOL_GPL(blkg_conf_prep);

block/blk-throttle.c

@@ -1154,21 +1154,25 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of,
 	struct blkcg_gq *blkg;
 	struct cgroup_subsys_state *pos_css;
 	int ret;
+	u64 v;
 
 	ret = blkg_conf_prep(blkcg, &blkcg_policy_throtl, buf, &ctx);
 	if (ret)
 		return ret;
 
+	ret = -EINVAL;
+	if (sscanf(ctx.body, "%llu", &v) != 1)
+		goto out_finish;
+	if (!v)
+		v = -1;
+
 	tg = blkg_to_tg(ctx.blkg);
 	sq = &tg->service_queue;
 
-	if (!ctx.v)
-		ctx.v = -1;
-
 	if (is_u64)
-		*(u64 *)((void *)tg + of_cft(of)->private) = ctx.v;
+		*(u64 *)((void *)tg + of_cft(of)->private) = v;
 	else
-		*(unsigned int *)((void *)tg + of_cft(of)->private) = ctx.v;
+		*(unsigned int *)((void *)tg + of_cft(of)->private) = v;
 
 	throtl_log(&tg->service_queue,
 		   "limit change rbps=%llu wbps=%llu riops=%u wiops=%u",
@@ -1201,8 +1205,10 @@ static ssize_t tg_set_conf(struct kernfs_open_file *of,
 		throtl_schedule_next_dispatch(sq->parent_sq, true);
 	}
 
+	ret = 0;
+out_finish:
 	blkg_conf_finish(&ctx);
-	return nbytes;
+	return ret ?: nbytes;
 }
 
 static ssize_t tg_set_conf_u64(struct kernfs_open_file *of,

block/cfq-iosched.c

@@ -1747,26 +1747,31 @@ static ssize_t __cfqg_set_weight_device(struct kernfs_open_file *of,
 	struct cfq_group *cfqg;
 	struct cfq_group_data *cfqgd;
 	int ret;
+	u64 v;
 
 	ret = blkg_conf_prep(blkcg, &blkcg_policy_cfq, buf, &ctx);
 	if (ret)
 		return ret;
 
+	ret = -EINVAL;
+	if (sscanf(ctx.body, "%llu", &v) != 1)
+		goto out_finish;
+
 	cfqg = blkg_to_cfqg(ctx.blkg);
 	cfqgd = blkcg_to_cfqgd(blkcg);
 
 	ret = -ERANGE;
-	if (!ctx.v || (ctx.v >= CFQ_WEIGHT_MIN && ctx.v <= CFQ_WEIGHT_MAX)) {
+	if (!v || (v >= CFQ_WEIGHT_MIN && v <= CFQ_WEIGHT_MAX)) {
 		if (!is_leaf_weight) {
-			cfqg->dev_weight = ctx.v;
-			cfqg->new_weight = ctx.v ?: cfqgd->weight;
+			cfqg->dev_weight = v;
+			cfqg->new_weight = v ?: cfqgd->weight;
 		} else {
-			cfqg->dev_leaf_weight = ctx.v;
-			cfqg->new_leaf_weight = ctx.v ?: cfqgd->leaf_weight;
+			cfqg->dev_leaf_weight = v;
+			cfqg->new_leaf_weight = v ?: cfqgd->leaf_weight;
 		}
 		ret = 0;
 	}
-
+out_finish:
 	blkg_conf_finish(&ctx);
 	return ret ?: nbytes;
 }

include/linux/blk-cgroup.h

@@ -206,11 +206,11 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
 struct blkg_conf_ctx {
 	struct gendisk			*disk;
 	struct blkcg_gq			*blkg;
-	u64				v;
+	char				*body;
 };
 
 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
-		   const char *input, struct blkg_conf_ctx *ctx);
+		   char *input, struct blkg_conf_ctx *ctx);
 void blkg_conf_finish(struct blkg_conf_ctx *ctx);