[PATCH v4] block: support mtd:<name> syntax for block devices

[Joakim Tjernlund <joakim.tjernlund@xxxxxxxxxxxx>]

This enables mounting, like JFFS2, MTD devices by "label":
   mount -t squashfs mtd:appfs /tmp
where mtd:appfs comes from:
 # >  cat /proc/mtd
dev:    size   erasesize  name
...
mtd22: 00750000 00010000 "appfs"

Signed-off-by: Joakim Tjernlund <joakim.tjernlund@xxxxxxxxxxxx>
---
 fs/super.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 97a17f9d9023..df7a6cfa34d3 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -37,6 +37,7 @@
 #include <linux/user_namespace.h>
 #include <linux/fs_context.h>
 #include <uapi/linux/mount.h>
+#include <linux/mtd/mtd.h>
 #include "internal.h"
 
 static int thaw_super_locked(struct super_block *sb, enum freeze_holder who);
@@ -1595,6 +1596,32 @@ int setup_bdev_super(struct super_block *sb, int sb_flags,
 }
 EXPORT_SYMBOL_GPL(setup_bdev_super);
 
+static int translate_mtd_name(struct fs_context *fc)
+{
+#ifdef CONFIG_MTD_BLOCK
+	if (!strncmp(fc->source, "mtd:", 4)) {
+		struct mtd_info *mtd;
+		char *blk_source;
+
+		/* mount by MTD device name */
+		pr_debug("Block SB: name \"%s\"\n", fc->source);
+
+		mtd = get_mtd_device_nm(fc->source + 4);
+		if (IS_ERR(mtd))
+			return -EINVAL;
+		blk_source = kmalloc(20, GFP_KERNEL);
+		if (!blk_source)
+			return -ENOMEM;
+		sprintf(blk_source, "/dev/mtdblock%d", mtd->index);
+		kfree(fc->source);
+		fc->source = blk_source;
+		pr_debug("MTD device:%s found\n", fc->source);
+		return 0;
+	}
+#endif
+	return 0;
+}
+
 /**
  * get_tree_bdev_flags - Get a superblock based on a single block device
  * @fc: The filesystem context holding the parameters
@@ -1612,6 +1639,9 @@ int get_tree_bdev_flags(struct fs_context *fc,
 	if (!fc->source)
 		return invalf(fc, "No source specified");
 
+	error = translate_mtd_name(fc);
+	if (error)
+		return error;
 	error = lookup_bdev(fc->source, &dev);
 	if (error) {
 		if (!(flags & GET_TREE_BDEV_QUIET_LOOKUP))
-- 
2.49.0