reiserfs: Deprecate reiserfs

Reiserfs is relatively old filesystem and its development has ceased
quite some years ago. Linux distributions moved away from it towards
other filesystems such as btrfs, xfs, or ext4. To reduce maintenance
burden on cross filesystem changes (such as new mount API, iomap, folios
...) let's add a deprecation notice when the filesystem is mounted and
schedule its removal to 2025.

Link: https://lore.kernel.org/r/20220225125445.29942-1-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>

fs/reiserfs/Kconfig

@@ -1,10 +1,14 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config REISERFS_FS
-	tristate "Reiserfs support"
+	tristate "Reiserfs support (deprecated)"
 	select CRC32
 	help
-	  Stores not just filenames but the files themselves in a balanced
-	  tree.  Uses journalling.
+	  Reiserfs is deprecated and scheduled to be removed from the kernel
+	  in 2025. If you are still using it, please migrate to another
+	  filesystem or tell us your usecase for reiserfs.
+
+	  Reiserfs stores not just filenames but the files themselves in a
+	  balanced tree.  Uses journalling.
 
 	  Balanced trees are more efficient than traditional file system
 	  architectural foundations.

fs/reiserfs/super.c

@@ -1652,6 +1652,8 @@ static int read_super_block(struct super_block *s, int offset)
 		return 1;
 	}
 
+	reiserfs_warning(NULL, "", "reiserfs filesystem is deprecated and "
+		"scheduled to be removed from the kernel in 2025");
 	SB_BUFFER_WITH_SB(s) = bh;
 	SB_DISK_SUPER_BLOCK(s) = rs;