[PATCH 2/3] Introduce the res_counter_populate() function

[Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>]

This one is responsible for initializing the RES_CFT_MAX files
properly and register them inside the container.

The caller must provide the cgroup, the cgroup_subsys, the
RES_CFT_MAX * sizeof(cftype) chunk of zeroed memory, the
units of measure and the read and write callbacks.

Right now I made names for two units - bytes and items. Maybe
later we will add more (pages, HZ?).

In the future, if we add more res_counter files, change their
names or anything else, no caller will be affected.

Signed-off-by: Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>

---

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index 61363ce..bee93c3 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -58,6 +58,17 @@ ssize_t res_counter_write(struct res_cou
 		const char __user *buf, size_t nbytes, loff_t *pos,
 		int (*write_strategy)(char *buf, unsigned long long *val));
 
+enum {
+	RES_UNITS_BYTES,
+	RES_UNITS_ITEMS,
+
+	RES_UNITS_MAX
+};
+
+int res_counter_populate(struct cgroup_subsys *ss, struct cgroup *cont,
+		struct cftype files[], int units,
+		cft_read read_fn, cft_write write_fn);
+
 /*
  * the field descriptors. one for each member of res_counter
  */
@@ -66,6 +77,8 @@ enum {
 	RES_USAGE,
 	RES_LIMIT,
 	RES_FAILCNT,
+
+	RES_CFT_MAX,
 };
 
 /*
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index d7f43cd..ae77b6e 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -10,9 +10,45 @@
 #include <linux/types.h>
 #include <linux/parser.h>
 #include <linux/fs.h>
+#include <linux/cgroup.h>
 #include <linux/res_counter.h>
 #include <linux/uaccess.h>
 
+static char * units_names[RES_UNITS_MAX][RES_CFT_MAX] = {
+	[RES_UNITS_BYTES] = {
+		"usage_in_bytes",
+		"limit_in_bytes",
+		"failcnt",
+	},
+	[RES_UNITS_ITEMS] = {
+		"usage",
+		"limit",
+		"failcnt",
+	},
+};
+
+static void cft_init(struct cftype files[], int type, int units,
+		cft_read read_fn, cft_write write_fn)
+{
+	if (files[type].name[0] == '\0') {
+		strcpy(files[type].name, units_names[units][type]);
+		files[type].private = type;
+		files[type].read = read_fn;
+		files[type].write = write_fn;
+	}
+}
+
+int res_counter_populate(struct cgroup_subsys *ss, struct cgroup *cont,
+		struct cftype files[], int units,
+		cft_read read_fn, cft_write write_fn)
+{
+	cft_init(files, RES_USAGE, units, read_fn, NULL);
+	cft_init(files, RES_LIMIT, units, read_fn, write_fn);
+	cft_init(files, RES_FAILCNT, units, read_fn, NULL);
+
+	return cgroup_add_files(cont, ss, files, RES_CFT_MAX);
+}
+
 void res_counter_init(struct res_counter *counter)
 {
 	spin_lock_init(&counter->lock);