hugetlb_cgroup: convert away from cftype->read()

In preparation of conversion to kernfs, cgroup file handling is being
consolidated so that it can be easily mapped to the seq_file based
interface of kernfs.

All users of cftype->read() can be easily served, usually better, by
seq_file and other methods.  Update hugetlb_cgroup_read() to return
u64 instead of printing itself and rename it to
hugetlb_cgroup_read_u64().

This patch doesn't make any visible behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>

mm/hugetlb_cgroup.c

@@ -242,22 +242,16 @@ void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,
 	return;
 }
 
-static ssize_t hugetlb_cgroup_read(struct cgroup_subsys_state *css,
-				   struct cftype *cft, struct file *file,
-				   char __user *buf, size_t nbytes,
-				   loff_t *ppos)
+static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
+				   struct cftype *cft)
 {
-	u64 val;
-	char str[64];
-	int idx, name, len;
+	int idx, name;
 	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);
 
 	idx = MEMFILE_IDX(cft->private);
 	name = MEMFILE_ATTR(cft->private);
 
-	val = res_counter_read_u64(&h_cg->hugepage[idx], name);
-	len = scnprintf(str, sizeof(str), "%llu\n", (unsigned long long)val);
-	return simple_read_from_buffer(buf, nbytes, ppos, str, len);
+	return res_counter_read_u64(&h_cg->hugepage[idx], name);
 }
 
 static int hugetlb_cgroup_write(struct cgroup_subsys_state *css,
@@ -337,28 +331,28 @@ static void __init __hugetlb_cgroup_file_init(int idx)
 	cft = &h->cgroup_files[0];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.limit_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_LIMIT);
-	cft->read = hugetlb_cgroup_read;
+	cft->read_u64 = hugetlb_cgroup_read_u64;
 	cft->write_string = hugetlb_cgroup_write;
 
 	/* Add the usage file */
 	cft = &h->cgroup_files[1];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.usage_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_USAGE);
-	cft->read = hugetlb_cgroup_read;
+	cft->read_u64 = hugetlb_cgroup_read_u64;
 
 	/* Add the MAX usage file */
 	cft = &h->cgroup_files[2];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.max_usage_in_bytes", buf);
 	cft->private = MEMFILE_PRIVATE(idx, RES_MAX_USAGE);
 	cft->trigger = hugetlb_cgroup_reset;
-	cft->read = hugetlb_cgroup_read;
+	cft->read_u64 = hugetlb_cgroup_read_u64;
 
 	/* Add the failcntfile */
 	cft = &h->cgroup_files[3];
 	snprintf(cft->name, MAX_CFTYPE_NAME, "%s.failcnt", buf);
 	cft->private  = MEMFILE_PRIVATE(idx, RES_FAILCNT);
 	cft->trigger  = hugetlb_cgroup_reset;
-	cft->read = hugetlb_cgroup_read;
+	cft->read_u64 = hugetlb_cgroup_read_u64;
 
 	/* NULL terminate the last cft */
 	cft = &h->cgroup_files[4];