mtd: concat: replace alloc + calloc with 1 alloc

A flex array can be used to reduce the allocation to 1.

And actually mtdconcat was using the pointer + 1 trick to point to the
overallocated area. Better alternatives exist.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: neheb

drivers/mtd/mtd_virt_concat.c

@@ -182,18 +182,12 @@ static int mtd_virt_concat_create_item(struct device_node *parts,
 	for (i = 1; i < count; i++)
 		item->nodes[i] = of_parse_phandle(parts, CONCAT_PROP, (i - 1));
 
-	concat = kzalloc(sizeof(*concat), GFP_KERNEL);
+	concat = kzalloc_flex(*concat, subdev, count, GFP_KERNEL);
 	if (!concat) {
 		kfree(item);
 		return -ENOMEM;
 	}
 
-	concat->subdev = kcalloc(count, sizeof(*concat->subdev), GFP_KERNEL);
-	if (!concat->subdev) {
-		kfree(item);
-		kfree(concat);
-		return -ENOMEM;
-	}
 	item->concat = concat;
 
 	list_add_tail(&item->head, &concat_node_list);

drivers/mtd/mtdconcat.c

@@ -627,7 +627,6 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 				   const char *name)
 {				/* name for the new device   */
 	int i;
-	size_t size;
 	struct mtd_concat *concat;
 	struct mtd_info *subdev_master = NULL;
 	uint32_t max_erasesize, curr_erasesize;
@@ -640,15 +639,13 @@ struct mtd_info *mtd_concat_create(struct mtd_info *subdev[],	/* subdevices to c
 	printk(KERN_NOTICE "into device \"%s\"\n", name);
 
 	/* allocate the device structure */
-	size = SIZEOF_STRUCT_MTD_CONCAT(num_devs);
-	concat = kzalloc(size, GFP_KERNEL);
+	concat = kzalloc_flex(*concat, subdev, num_devs, GFP_KERNEL);
 	if (!concat) {
 		printk
 		    ("memory allocation error while creating concatenated device \"%s\"\n",
 		     name);
 		return NULL;
 	}
-	concat->subdev = (struct mtd_info **) (concat + 1);
 
 	/*
 	 * Set up the new "super" device's MTD object structure, check for

include/linux/mtd/concat.h

@@ -18,7 +18,7 @@
 struct mtd_concat {
 	struct mtd_info mtd;
 	int num_subdev;
-	struct mtd_info **subdev;
+	struct mtd_info *subdev[];
 };
 
 struct mtd_info *mtd_concat_create(