udev: Fit into the standard rule sequence

Move the rule to run a bit later, after
the standard udev rules have called blkid.

Don't run blkid manually, and run probe-bcache
as a fallback which can be patched out in a
package that depends on util-linux 2.24+.

probe-bcache: bail if libblkid finds anything
Preserve our last-resort safety check here
in case earlier rules fail to call blkid.

61-bcache.rules → 69-bcache.rules

@@ -4,13 +4,18 @@
 SUBSYSTEM!="block", GOTO="bcache_end"
 ACTION=="remove", GOTO="bcache_end"
 
-# Backing devices: scan, symlink, register
-IMPORT{program}="/sbin/blkid -o udev $tempnode"
-# blkid and probe-bcache can disagree, in which case don't register
-ENV{ID_FS_TYPE}=="?*", ENV{ID_FS_TYPE}!="bcache", GOTO="bcache_backing_end"
+# blkid was run by the standard udev rules
+# It recognised bcache (util-linux 2.24+)
+ENV{ID_FS_TYPE}=="bcache", GOTO="bcache_backing_found"
+# It recognised something else; bail
+ENV{ID_FS_TYPE}=="?*", GOTO="bcache_backing_end"
 
+# Backing devices: scan, symlink, register
 IMPORT{program}="/sbin/probe-bcache -o udev $tempnode"
+ENV{ID_FS_TYPE}!="bcache", GOTO="bcache_backing_end"
 ENV{ID_FS_UUID_ENC}=="?*", SYMLINK+="disk/by-uuid/$env{ID_FS_UUID_ENC}"
+
+LABEL="bcache_backing_found"
 SUBSYSTEM=="block", ACTION=="add|change", ENV{ID_FS_TYPE}=="bcache", \
         RUN+="bcache-register $tempnode"
 LABEL="bcache_backing_end"

Makefile

@@ -7,7 +7,7 @@ all: make-bcache probe-bcache bcache-super-show
 install: make-bcache probe-bcache bcache-super-show
 	install -m0755 make-bcache bcache-super-show	$(DESTDIR)${PREFIX}/sbin/
 	install -m0755 probe-bcache	$(DESTDIR)/sbin/
-	install -m0644 61-bcache.rules	$(DESTDIR)/lib/udev/rules.d/
+	install -m0644 69-bcache.rules	$(DESTDIR)/lib/udev/rules.d/
 	install -m0755 bcache-register	$(DESTDIR)/lib/udev/
 	-install -T -m0755 initramfs/hook	$(DESTDIR)/usr/share/initramfs-tools/hooks/bcache
 	install -m0644 -- *.8 $(DESTDIR)${PREFIX}/share/man/man8/
@@ -20,7 +20,8 @@ bcache-test: LDLIBS += `pkg-config --libs openssl`
 make-bcache: LDLIBS += `pkg-config --libs uuid blkid`
 make-bcache: CFLAGS += `pkg-config --cflags uuid blkid`
 make-bcache: bcache.o
-probe-bcache: LDLIBS += `pkg-config --libs uuid`
+probe-bcache: LDLIBS += `pkg-config --libs uuid blkid`
+probe-bcache: CFLAGS += `pkg-config --cflags uuid blkid`
 bcache-super-show: LDLIBS += `pkg-config --libs uuid`
 bcache-super-show: CFLAGS += -std=gnu99
 bcache-super-show: bcache.o

initramfs/hook

@@ -16,7 +16,7 @@ esac
 
 . /usr/share/initramfs-tools/hook-functions
 
-cp -pt "${DESTDIR}/lib/udev/rules.d" /lib/udev/rules.d/61-bcache.rules
+cp -pt "${DESTDIR}/lib/udev/rules.d" /lib/udev/rules.d/69-bcache.rules
 copy_exec /lib/udev/bcache-register
 copy_exec /sbin/probe-bcache
 manual_add_modules bcache

probe-bcache.c

@@ -8,6 +8,7 @@
 #define __USE_FILE_OFFSET64
 #define _XOPEN_SOURCE 500
 
+#include <blkid.h>
 #include <fcntl.h>
 #include <linux/fs.h>
 #include <stdbool.h>
@@ -30,6 +31,7 @@ int main(int argc, char **argv)
 	extern char *optarg;
 	struct cache_sb sb;
 	char uuid[40];
+	blkid_probe pr;
 
 	while ((o = getopt(argc, argv, "o:")) != EOF)
 		switch (o) {
@@ -51,6 +53,18 @@ int main(int argc, char **argv)
 		if (fd == -1)
 			continue;
 
+		if (!(pr = blkid_new_probe()))
+			continue;
+		if (blkid_probe_set_device(pr, fd, 0, 0))
+			continue;
+		/* probe partitions too */
+		if (blkid_probe_enable_partitions(pr, true))
+			continue;
+		/* bail if anything was found
+		 * probe-bcache isn't needed once blkid recognizes bcache */
+		if (!blkid_do_probe(pr)) {
+			continue;
+		}
 
 		if (pread(fd, &sb, sizeof(sb), SB_START) != sizeof(sb))
 			continue;