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>

3 files changed, 37 insertions, 20 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 429726bed560..8ee1ca4d4f2f 100644
--- a/block/blk-cgroup.c
+++ b/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);
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 8b4f6b81bb72..0e17c8f92d25 100644
--- a/block/blk-throttle.c
+++ b/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,
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index baa8459f7064..ea88d8905bbd 100644
--- a/block/cfq-iosched.c
+++ b/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;
 }