Allow choice of mountable writes by default

A distro packager has requested writable mounts by default, and is
willing to take responsibility for any potential harm to their users:

  #81

Add a build flag to enable this, but leave it undocumented to avoid
confusing anyone.

Signed-off-by: Ernesto A. Fernández <ernesto@corellium.com>

Author: eafer

Makefile

@@ -13,6 +13,11 @@ apfs-y := btree.o compress.o dir.o extents.o file.o inode.o key.o libzbitmap.o \
 	  lzfse/lzvn_decode_base.o message.o namei.o node.o object.o snapshot.o \
 	  spaceman.o super.o symlink.o transaction.o unicode.o xattr.o xfield.o
 
+# If you want mounts to be writable by default, run the build as:
+#   make CONFIG=-DCONFIG_APFS_RW_ALWAYS
+# This is risky and not generally recommended.
+ccflags-y += $(CONFIG)
+
 default:
 	./genver.sh
 	make -C $(KERNEL_DIR) M=$(PWD)

super.c

@@ -1194,6 +1194,11 @@ static int parse_options(struct super_block *sb, char *options)
 	/* Set default values before parsing */
 	nx_flags = 0;
 
+#ifdef CONFIG_APFS_RW_ALWAYS
+	/* Still risky, but some packagers want writable mounts by default */
+	nx_flags |= APFS_READWRITE;
+#endif
+
 	if (!options)
 		goto out;