Add a command to display a bcache superblock.

.gitignore

@@ -1,3 +1,4 @@
+bcache-super-show
 make-bcache
 probe-bcache
 .*

Makefile

@@ -2,21 +2,23 @@
 PREFIX=/usr
 CFLAGS+=-O2 -Wall -g
 
-all: make-bcache probe-bcache
+all: make-bcache probe-bcache bcache-super-show
 
-install: make-bcache probe-bcache
-	install -m0755 make-bcache	$(DESTDIR)${PREFIX}/sbin/
+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 -m0755 initramfs/script $(DESTDIR)/etc/initramfs-tools/scripts/init-premount/bcache
 	-install -m0755 initramfs/hook	$(DESTDIR)/etc/initramfs-tools/hooks/bcache
-	install -m0644 *.8 $(DESTDIR)${PREFIX}/share/man/man8
+	install -m0644 -- *.8 $(DESTDIR)${PREFIX}/share/man/man8
 #	install -m0755 bcache-test $(DESTDIR)${PREFIX}/sbin/
 
 clean:
-	$(RM) -f make-bcache probe-bcache bcache-test *.o
+	$(RM) -f make-bcache probe-bcache bcache-super-show bcache-test *.o
 
 bcache-test: LDLIBS += -lm -lssl -lcrypto
 make-bcache: LDLIBS += -luuid
 make-bcache: bcache.o
 probe-bcache: LDLIBS += -luuid
+bcache-super-show: LDLIBS += -luuid
+bcache-super-show: bcache.o

README

@@ -22,3 +22,6 @@ Only necessary until support for the bcache superblock is included
 in blkid; in the meantime, provides just enough functionality for a udev script
 to create the /dev/disk/by-uuid symlink. The arguments it does support are the
 same as for blkid.
+
+bcache-super-show
+Prints the bcache superblock of a cache device or a backing device.

bcache-super-show.c

@@ -0,0 +1,145 @@
+#define _FILE_OFFSET_BITS	64
+#define __USE_FILE_OFFSET64
+#define _XOPEN_SOURCE 500
+
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <linux/fs.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <uuid/uuid.h>
+
+#include "bcache.h"
+
+
+static void usage()
+{
+	fprintf(stderr, "Usage: bcache-super-show [-f] <device>\n");
+}
+
+
+int main(int argc, char **argv)
+{
+	bool force_csum = false;
+	int o;
+	extern char *optarg;
+	struct cache_sb sb;
+	char uuid[40];
+	uint64_t expected_csum;
+
+	while ((o = getopt(argc, argv, "f")) != EOF)
+		switch (o) {
+			case 'f':
+				force_csum = 1;
+				break;
+
+			default:
+				usage();
+				exit(1);
+		}
+
+	argv += optind;
+	argc -= optind;
+
+	if (argc != 1) {
+		usage();
+		exit(1);
+	}
+
+	int fd = open(argv[0], O_RDONLY);
+	if (fd < 0) {
+		printf("Can't open dev %s: %s\n", argv[0], strerror(errno));
+		exit(2);
+	}
+
+	if (pread(fd, &sb, sizeof(sb), 4096) != sizeof(sb)) {
+		fprintf(stderr, "Couldn't read\n");
+		exit(2);
+	}
+
+	printf("sb.magic\t\t");
+	if (! memcmp(sb.magic, bcache_magic, 16)) {
+		printf("ok\n");
+	} else {
+		printf("bad magic\n");
+		fprintf(stderr, "Invalid superblock (bad magic)\n");
+		exit(2);
+	}
+
+	printf("sb.first_sector\t\t%" PRIu64, sb.offset);
+	if (sb.offset == SB_SECTOR) {
+		printf(" [match]\n");
+	} else {
+		printf(" [expected %ds]\n", SB_SECTOR);
+		fprintf(stderr, "Invalid superblock (bad sector)\n");
+		exit(2);
+	}
+
+	printf("sb.csum\t\t\t0x%" PRIx64, sb.csum);
+	expected_csum = csum_set(&sb);
+	if (sb.csum == expected_csum) {
+		printf(" [match]\n");
+	} else {
+		printf(" [expected %" PRIX64 "]\n", expected_csum);
+		if (! force_csum) {
+			fprintf(stderr, "Corrupt superblock (bad csum)\n");
+			exit(2);
+		}
+	}
+
+	printf("sb.version\t\t%" PRIu64, sb.version);
+	switch (sb.version) {
+		case 1:
+			printf(" [backing device]\n");
+			break;
+
+		case 2:
+			printf(" [cache device]\n");
+			break;
+
+		case 3:
+			printf(" [backing device with offset]\n");
+			// XXX Kernel side bcache.h says different, and implements neither
+			return 0; //break;
+
+		default:
+			printf(" [unknown]\n");
+			// exit code?
+			return 0;
+	}
+
+	putchar('\n');
+
+	uuid_unparse(sb.uuid, uuid);
+	printf("dev.uuid\t\t%s\n", uuid);
+
+	printf(
+			"dev.sectors_per_block\t%u\n"
+			"dev.sectors_per_bucket\t%u\n"
+			"dev.bucket_count\t%ju\n"
+			"dev.cache_count\t\t%u\n" // expect version == 2 ? 1 : 0
+			"dev.data.first_bucket\t%u\n",
+			sb.block_size,
+			sb.bucket_size,
+			sb.nbuckets,
+			sb.nr_this_dev,
+			sb.first_bucket);
+
+	printf("dev.data.first_sector\t%u\n", sb.bucket_size * sb.first_bucket);
+	putchar('\n');
+
+	uuid_unparse(sb.set_uuid, uuid);
+	printf("cset.uuid\t\t%s\n", uuid);
+
+	printf("cset.cache_count\t%u\n\n", sb.nr_in_set);
+
+	return 0;
+}