fs: make binfmt support for #! scripts modular and removable

Add a new configuration option CONFIG_BINFMT_SCRIPT to configure support
for interpreted scripts starting with "#!"; allow compiling out that
support, or building it as a module.  Embedded systems running exclusively
compiled binaries could leave this support out, and systems that don't
need scripts before mounting the root filesystem can build this as a
module.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/Kconfig.binfmt

@@ -65,6 +65,20 @@ config CORE_DUMP_DEFAULT_ELF_HEADERS
 	  This config option changes the default setting of coredump_filter
 	  seen at boot time.  If unsure, say Y.
 
+config BINFMT_SCRIPT
+	tristate "Kernel support for scripts starting with #!"
+	default y
+	help
+	  Say Y here if you want to execute interpreted scripts starting with
+	  #! followed by the path to an interpreter.
+
+	  You can build this support as a module; however, until that module
+	  gets loaded, you cannot run scripts.  Thus, if you want to load this
+	  module from an initramfs, the portion of the initramfs before loading
+	  this module must consist of compiled binaries only.
+
+	  Most systems will not boot if you say M or N here.  If unsure, say Y.
+
 config BINFMT_FLAT
 	bool "Kernel support for flat binaries"
 	depends on !MMU && (!FRV || BROKEN)

fs/Makefile

@@ -34,10 +34,7 @@ obj-$(CONFIG_COMPAT)		+= compat.o compat_ioctl.o
 obj-$(CONFIG_BINFMT_AOUT)	+= binfmt_aout.o
 obj-$(CONFIG_BINFMT_EM86)	+= binfmt_em86.o
 obj-$(CONFIG_BINFMT_MISC)	+= binfmt_misc.o
-
-# binfmt_script is always there
-obj-y				+= binfmt_script.o
-
+obj-$(CONFIG_BINFMT_SCRIPT)	+= binfmt_script.o
 obj-$(CONFIG_BINFMT_ELF)	+= binfmt_elf.o
 obj-$(CONFIG_COMPAT_BINFMT_ELF)	+= compat_binfmt_elf.o
 obj-$(CONFIG_BINFMT_ELF_FDPIC)	+= binfmt_elf_fdpic.o