composefs: Add kconfig and build support

This commit adds Makefile and Kconfig for composefs, and
updates Makefile and Kconfig files in the fs directory

Signed-off-by: Alexander Larsson <alexl@redhat.com>

fs/Kconfig

@@ -127,6 +127,7 @@ source "fs/quota/Kconfig"
 source "fs/autofs/Kconfig"
 source "fs/fuse/Kconfig"
 source "fs/overlayfs/Kconfig"
+source "fs/composefs/Kconfig"
 
 menu "Caches"
 

fs/Makefile

@@ -137,3 +137,4 @@ obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
 obj-$(CONFIG_EROFS_FS)		+= erofs/
 obj-$(CONFIG_VBOXSF_FS)		+= vboxsf/
 obj-$(CONFIG_ZONEFS_FS)		+= zonefs/
+obj-$(CONFIG_COMPOSEFS_FS)	+= composefs/

fs/composefs/Kconfig

@@ -0,0 +1,18 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+config COMPOSEFS_FS
+	tristate "Composefs filesystem support"
+	select EXPORTFS
+	help
+	  Composefs is a filesystem that allows combining file content from
+	  existing regular files with a metadata directory structure from
+	  a separate binary file. This is useful to share file content between
+	  many different directory trees, such as in a local container image store.
+
+	  Composefs also allows using fs-verity to validate the content of the
+	  content-files as well as the metadata file which allows dm-verity
+	  like validation with the flexibility of regular files.
+
+	  For more information see Documentation/filesystems/composefs.rst
+
+	  If unsure, say N.

fs/composefs/Makefile

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_COMPOSEFS_FS) += composefs.o
+
+composefs-objs += cfs-reader.o cfs.o