sunrpc: refactor pool_mode setting code

Allow the pool_mode setting code to be called from internal callers
so we can call it from a new netlink op. Add a new svc_pool_map_get
function to return the current setting. Change the existing module
parameter handling to use the new interfaces under the hood.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

include/linux/sunrpc/svc.h

@@ -399,6 +399,8 @@ struct svc_procedure {
 /*
  * Function prototypes.
  */
+int sunrpc_set_pool_mode(const char *val);
+int sunrpc_get_pool_mode(char *val, size_t size);
 int svc_rpcb_setup(struct svc_serv *serv, struct net *net);
 void svc_rpcb_cleanup(struct svc_serv *serv, struct net *net);
 int svc_bind(struct svc_serv *serv, struct net *net);

net/sunrpc/svc.c

@@ -72,57 +72,100 @@ static struct svc_pool_map svc_pool_map = {
 static DEFINE_MUTEX(svc_pool_map_mutex);/* protects svc_pool_map.count only */
 
 static int
-param_set_pool_mode(const char *val, const struct kernel_param *kp)
+__param_set_pool_mode(const char *val, struct svc_pool_map *m)
 {
-	int *ip = (int *)kp->arg;
-	struct svc_pool_map *m = &svc_pool_map;
-	int err;
+	int err, mode;
 
 	mutex_lock(&svc_pool_map_mutex);
 
-	err = -EBUSY;
-	if (m->count)
-		goto out;
-
 	err = 0;
 	if (!strncmp(val, "auto", 4))
-		*ip = SVC_POOL_AUTO;
+		mode = SVC_POOL_AUTO;
 	else if (!strncmp(val, "global", 6))
-		*ip = SVC_POOL_GLOBAL;
+		mode = SVC_POOL_GLOBAL;
 	else if (!strncmp(val, "percpu", 6))
-		*ip = SVC_POOL_PERCPU;
+		mode = SVC_POOL_PERCPU;
 	else if (!strncmp(val, "pernode", 7))
-		*ip = SVC_POOL_PERNODE;
+		mode = SVC_POOL_PERNODE;
 	else
 		err = -EINVAL;
 
+	if (err)
+		goto out;
+
+	if (m->count == 0)
+		m->mode = mode;
+	else if (mode != m->mode)
+		err = -EBUSY;
 out:
 	mutex_unlock(&svc_pool_map_mutex);
 	return err;
 }
 
 static int
-param_get_pool_mode(char *buf, const struct kernel_param *kp)
+param_set_pool_mode(const char *val, const struct kernel_param *kp)
+{
+	struct svc_pool_map *m = kp->arg;
+
+	return __param_set_pool_mode(val, m);
+}
+
+int sunrpc_set_pool_mode(const char *val)
 {
-	int *ip = (int *)kp->arg;
+	return __param_set_pool_mode(val, &svc_pool_map);
+}
+EXPORT_SYMBOL(sunrpc_set_pool_mode);
 
-	switch (*ip)
+/**
+ * sunrpc_get_pool_mode - get the current pool_mode for the host
+ * @buf: where to write the current pool_mode
+ * @size: size of @buf
+ *
+ * Grab the current pool_mode from the svc_pool_map and write
+ * the resulting string to @buf. Returns the number of characters
+ * written to @buf (a'la snprintf()).
+ */
+int
+sunrpc_get_pool_mode(char *buf, size_t size)
+{
+	struct svc_pool_map *m = &svc_pool_map;
+
+	switch (m->mode)
 	{
 	case SVC_POOL_AUTO:
-		return sysfs_emit(buf, "auto\n");
+		return snprintf(buf, size, "auto");
 	case SVC_POOL_GLOBAL:
-		return sysfs_emit(buf, "global\n");
+		return snprintf(buf, size, "global");
 	case SVC_POOL_PERCPU:
-		return sysfs_emit(buf, "percpu\n");
+		return snprintf(buf, size, "percpu");
 	case SVC_POOL_PERNODE:
-		return sysfs_emit(buf, "pernode\n");
+		return snprintf(buf, size, "pernode");
 	default:
-		return sysfs_emit(buf, "%d\n", *ip);
+		return snprintf(buf, size, "%d", m->mode);
 	}
 }
+EXPORT_SYMBOL(sunrpc_get_pool_mode);
+
+static int
+param_get_pool_mode(char *buf, const struct kernel_param *kp)
+{
+	char str[16];
+	int len;
+
+	len = sunrpc_get_pool_mode(str, ARRAY_SIZE(str));
+
+	/* Ensure we have room for newline and NUL */
+	len = min_t(int, len, ARRAY_SIZE(str) - 2);
+
+	/* tack on the newline */
+	str[len] = '\n';
+	str[len + 1] = '\0';
+
+	return sysfs_emit(buf, str);
+}
 
 module_param_call(pool_mode, param_set_pool_mode, param_get_pool_mode,
-		 &svc_pool_map.mode, 0644);
+		  &svc_pool_map, 0644);
 
 /*
  * Detect best pool mapping mode heuristically,