hfsfuse: make extended attribute namespace configurable

Changes this to a build-time make parameter XATTR_NAMESPACE which can
be used to select other namespaces than the OS default.

Allows the platform dependent checks for this to be moved out to the
build system and provides a means for accessing symlink extended
attributes on Linux, which can't be read under the user namespace.

Author: 0x09

Makefile

@@ -22,9 +22,11 @@ TARGETS = hfsfuse hfsdump
 FUSE_FLAGS = -DFUSE_USE_VERSION=28
 FUSE_LIB = -lfuse
 
+XATTR_NAMESPACE = user.
 ifeq ($(OS), Darwin)
 	APP_FLAGS += -I/usr/local/include
 	APP_LIB += -L/usr/local/lib
+	XATTR_NAMESPACE = #no namespaces on macOS
 	ifeq ($(shell [ -e /usr/local/lib/libosxfuse.dylib ] && echo 1), 1)
 		FUSE_FLAGS += -I/usr/local/include/osxfuse
 		FUSE_LIB = -losxfuse
@@ -134,7 +136,7 @@ ifneq ($(filter-out $(non_build_targets),$(or $(MAKECMDGOALS),all)),)
     $(eval $(call cccheck,HAVE_ZLIB,,zlib.h))
 endif
 
-$(foreach cfg,OS CC AR RANLIB INSTALL TAR PREFIX WITH_UBLIO WITH_UTF8PROC CONFIG_CFLAGS $(FEATURES),$(eval CONFIG:=$(CONFIG)$(cfg)=$$($(cfg))\n))
+$(foreach cfg,OS CC AR RANLIB INSTALL TAR PREFIX WITH_UBLIO WITH_UTF8PROC XATTR_NAMESPACE CONFIG_CFLAGS $(FEATURES),$(eval CONFIG:=$(CONFIG)$(cfg)=$$($(cfg))\n))
 $(foreach feature,$(FEATURES),$(if $(filter $($(feature)),1),$(eval CFLAGS+=-D$(feature))))
 
 LIBS = lib/libhfsuser/libhfsuser.a lib/libhfs/libhfs.a
@@ -189,7 +191,7 @@ all: $(TARGETS)
 %.o: CPPFLAGS += $(INCLUDE)
 %.o: CFLAGS += $(LOCAL_CFLAGS)
 
-src/hfsfuse.o: CPPFLAGS += $(FUSE_FLAGS)
+src/hfsfuse.o: CPPFLAGS += $(FUSE_FLAGS) -DXATTR_NAMESPACE=$(XATTR_NAMESPACE)
 
 $(LIBS): always_check
 	$(MAKE) -C $(dir $@)
@@ -239,4 +241,8 @@ config:
 	@echo "$$CONFIG" > config.mak
 
 dist: version
-	git archive master -o "$(RELEASE_NAME).tar.gz" --prefix "$(RELEASE_NAME)/src/" --add-file src/version.h --prefix "$(RELEASE_NAME)/"
+	#git archive master -o "$(RELEASE_NAME).tar.gz" --prefix "$(RELEASE_NAME)/src/" --add-file src/version.h --prefix "$(RELEASE_NAME)/"
+	ln -s . $(RELEASE_NAME)
+	$(RM) -- $(RELEASE_NAME).tar.gz
+	git ls-files | sed "s/^/$(RELEASE_NAME)\//" | COPYFILE_DISABLE=1 $(TAR) --no-xattrs -czf $(RELEASE_NAME).tar.gz -T - -- $(RELEASE_NAME)/src/version.h
+	$(RM) -- $(RELEASE_NAME)

README.md

@@ -135,6 +135,8 @@ Under Haiku only, all extended attribute values are hex encoded to allow binary
 catattr -r user.com.apple.ResourceFork file | xxd -r -p
 ```
 
+Extended attributes are presented in the preferred namespace for the OS, typically `user.`. Alternate namespaces may be chosen when building hfsfuse by setting the `XATTR_NAMESPACE` make var.  
+This should include the trailing `.` as an empty value indicates no namespacing (such as on macOS.)
 
 ## Mac OS Classic file permissions
 HFS+ filesystems created on Mac OS Classic do not contain the typical set of Unix ownership and permission information for files and folders.

src/hfsfuse.c

@@ -300,11 +300,10 @@ static int hfsfuse_getxtimes(const char* path, struct timespec* bkuptime, struct
 }
 #endif
 
-#ifdef __APPLE__
-#define attrname(name) name
-#else
-#define attrname(name) "user." name
-#endif
+#define STR_(x) #x
+#define STR(x) STR_(x)
+#define XATTR_NAMESPACE_STR STR(XATTR_NAMESPACE)
+#define attrname(name) XATTR_NAMESPACE_STR name
 
 #define declare_attr(name, buf, bufsize, accum) do {\
 	accum += strlen(attrname(name))+1;\
@@ -350,14 +349,9 @@ static int hfsfuse_listxattr(const char* path, char* attr, size_t size) {
 		ssize_t u8len = hfs_unistr_to_utf8(&attr_keys[i].name, attrname);
 		if(u8len <= 0)
 			continue;
-		ret += u8len + 1;
-#ifndef __APPLE__
-		ret += 5; //user. prefix
-#endif
+		ret += u8len + strlen(XATTR_NAMESPACE_STR) + 1;
 		if(size >= (size_t)ret) {
-#ifndef __APPLE__
-			attr = stpcpy(attr, "user.");
-#endif
+			attr = stpcpy(attr, XATTR_NAMESPACE_STR);
 			attr = stpcpy(attr, attrname)+1;
 		}
 	}
@@ -421,10 +415,8 @@ static int hfsfuse_getxattr_offset(const char* path, const char* attr, char* val
 		memcpy(value, timebuf, 24);
 	});
 
-#ifndef __APPLE__
-	if(!strncmp(attr,"user.",5))
-		attr += 5;
-#endif
+	if(!strncmp(attr,XATTR_NAMESPACE_STR,strlen(XATTR_NAMESPACE_STR)))
+		attr += strlen(XATTR_NAMESPACE_STR);
 
 	hfs_attribute_record_t attrec;
 	hfs_unistr255_t attrname;