ovl: fix some xino configurations

Fix up two bugs in the coversion to xino_mode:
1. xino=off does not always end up in disabled mode
2. xino=auto on 32bit arch should end up in disabled mode

Take a proactive approach to disabling xino on 32bit kernel:
1. Disable XINO_AUTO config during build time
2. Disable xino with a warning on mount time

As a by product, xino=on on 32bit arch also ends up in disabled mode.
We never intended to enable xino on 32bit arch and this will make the
rest of the logic simpler.

Fixes: 0f831ec ("ovl: simplify ovl_same_sb() helper")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Author: amir73il

fs/overlayfs/Kconfig

@@ -93,6 +93,7 @@ config OVERLAY_FS_XINO_AUTO
 	bool "Overlayfs: auto enable inode number mapping"
 	default n
 	depends on OVERLAY_FS
+	depends on 64BIT
 	help
 	  If this config option is enabled then overlay filesystems will use
 	  unused high bits in undelying filesystem inode numbers to map all

fs/overlayfs/super.c

@@ -1411,6 +1411,8 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 		if (ofs->config.xino == OVL_XINO_ON)
 			pr_info("\"xino=on\" is useless with all layers on same fs, ignore.\n");
 		ofs->xino_mode = 0;
+	} else if (ofs->config.xino == OVL_XINO_OFF) {
+		ofs->xino_mode = -1;
 	} else if (ofs->config.xino == OVL_XINO_ON && ofs->xino_mode < 0) {
 		/*
 		 * This is a roundup of number of bits needed for encoding
@@ -1623,8 +1625,13 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_stack_depth = 0;
 	sb->s_maxbytes = MAX_LFS_FILESIZE;
 	/* Assume underlaying fs uses 32bit inodes unless proven otherwise */
-	if (ofs->config.xino != OVL_XINO_OFF)
+	if (ofs->config.xino != OVL_XINO_OFF) {
 		ofs->xino_mode = BITS_PER_LONG - 32;
+		if (!ofs->xino_mode) {
+			pr_warn("xino not supported on 32bit kernel, falling back to xino=off.\n");
+			ofs->config.xino = OVL_XINO_OFF;
+		}
+	}
 
 	/* alloc/destroy_inode needed for setting up traps in inode cache */
 	sb->s_op = &ovl_super_operations;