[MTD] add get_mtd_device_nm() function

This patch adds one more function to the MTD interface to make it possible to
open MTD devices by their names, not only numbers. This is very handy in many
situations. Also, MTD device number depend on load order and may vary, while
names are fixed.
Signed-off-by: Artem Bityutskiy <dedekind@infradead.org>

drivers/mtd/mtdcore.c

@@ -15,6 +15,7 @@
 #include <linux/timer.h>
 #include <linux/major.h>
 #include <linux/fs.h>
+#include <linux/err.h>
 #include <linux/ioctl.h>
 #include <linux/init.h>
 #include <linux/mtd/compatmac.h>
@@ -223,6 +224,42 @@ struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num)
 	return ret;
 }
 
+/**
+ *	get_mtd_device_nm - obtain a validated handle for an MTD device by
+ *	device name
+ *	@name: MTD device name to open
+ *
+ * 	This function returns MTD device description structure in case of
+ * 	success and an error code in case of failure.
+ */
+
+struct mtd_info *get_mtd_device_nm(const char *name)
+{
+	int i;
+	struct mtd_info *mtd = ERR_PTR(-ENODEV);
+
+	mutex_lock(&mtd_table_mutex);
+
+	for (i = 0; i < MAX_MTD_DEVICES; i++) {
+		if (mtd_table[i] && !strcmp(name, mtd_table[i]->name)) {
+			mtd = mtd_table[i];
+			break;
+		}
+	}
+
+	if (i == MAX_MTD_DEVICES)
+		goto out_unlock;
+
+	if (!try_module_get(mtd->owner))
+		goto out_unlock;
+
+	mtd->usecount++;
+
+out_unlock:
+	mutex_unlock(&mtd_table_mutex);
+	return mtd;
+}
+
 void put_mtd_device(struct mtd_info *mtd)
 {
 	int c;
@@ -267,6 +304,7 @@ int default_mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
 EXPORT_SYMBOL(add_mtd_device);
 EXPORT_SYMBOL(del_mtd_device);
 EXPORT_SYMBOL(get_mtd_device);
+EXPORT_SYMBOL(get_mtd_device_nm);
 EXPORT_SYMBOL(put_mtd_device);
 EXPORT_SYMBOL(register_mtd_user);
 EXPORT_SYMBOL(unregister_mtd_user);

include/linux/mtd/mtd.h

@@ -216,6 +216,7 @@ extern int add_mtd_device(struct mtd_info *mtd);
 extern int del_mtd_device (struct mtd_info *mtd);
 
 extern struct mtd_info *get_mtd_device(struct mtd_info *mtd, int num);
+extern struct mtd_info *get_mtd_device_nm(const char *name);
 
 extern void put_mtd_device(struct mtd_info *mtd);