bcache data offset

Add a new superblock version, and consolidate related defines.

Signed-off-by Gabriel de Perthuis <[email protected]>

---
 drivers/md/bcache/bcache.h  | 23 ++++++++++++++++++-----
 drivers/md/bcache/request.c |  2 +-
 drivers/md/bcache/super.c   | 21 ++++++++++++++++-----
 3 files changed, 35 insertions(+), 11 deletions(-)

drivers/md/bcache/bcache.h +18 -5

index f057235..8a110e6 100644
@@ -223,11 +223,17 @@ struct bkey {
 #define BKEY_PADDED(key)					\
 	union { struct bkey key; uint64_t key ## _pad[BKEY_PAD]; }
 
-/* Version 1: Backing device
+/* Version 0: Cache device
+ * Version 1: Backing device
  * Version 2: Seed pointer into btree node checksum
- * Version 3: New UUID format
+ * Version 3: Cache device with new UUID format
+ * Version 4: Backing device with data offset
  */
-#define BCACHE_SB_VERSION	3
+#define BCACHE_SB_VERSION_CDEV			0
+#define BCACHE_SB_VERSION_BDEV			1
+#define BCACHE_SB_VERSION_CDEV_WITH_UUID	3
+#define BCACHE_SB_VERSION_BDEV_WITH_OFFSET	4
+#define BCACHE_SB_MAX_VERSION			4
 
 #define SB_SECTOR		8
 #define SB_SIZE			4096

@@ -236,13 +242,12 @@ struct bkey {
 /* SB_JOURNAL_BUCKETS must be divisible by BITS_PER_LONG */
 #define MAX_CACHES_PER_SET	8
 
-#define BDEV_DATA_START		16	/* sectors */
+#define BDEV_DATA_START_DEFAULT	16	/* sectors */
 
 struct cache_sb {
 	uint64_t		csum;
 	uint64_t		offset;	/* sector where this sb was written */
 	uint64_t		version;
-#define CACHE_BACKING_DEV	1
 
 	uint8_t			magic[16];
 

@@ -485,6 +490,7 @@ struct cached_dev {
 	 * where it's at.
 	 */
 	sector_t		last_read;
+	sector_t		data_start_sector;
 
 	/* Number of writeback bios in flight */
 	atomic_t		in_flight;

@@ -861,6 +867,13 @@ static inline bool key_merging_disabled(struct cache_set *c)
 #endif
 }
 
+
+static inline bool SB_IS_BDEV(const struct cache_sb *sb) {
+	return sb->version == BCACHE_SB_VERSION_BDEV
+		|| sb->version == BCACHE_SB_VERSION_BDEV_WITH_OFFSET;
+}
+
+
 struct bbio {
 	unsigned		submit_time_us;
 	union {

drivers/md/bcache/request.c +1 -1

index 83731dc..9f74aff 100644
@@ -1220,7 +1220,7 @@ static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
 	part_stat_unlock();
 
 	bio->bi_bdev = dc->bdev;
-	bio->bi_sector += BDEV_DATA_START;
+	bio->bi_sector += dc->data_start_sector;
 
 	if (cached_dev_get(dc)) {
 		s = search_alloc(bio, d);

drivers/md/bcache/super.c +16 -5

index 5fa3cd2..a409bb5 100644
@@ -148,7 +148,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
 		goto err;
 
 	err = "Unsupported superblock version";
-	if (sb->version > BCACHE_SB_VERSION)
+	if (sb->version > BCACHE_SB_MAX_VERSION)
 		goto err;
 
 	err = "Bad block/bucket size";

@@ -168,7 +168,7 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
 	if (get_capacity(bdev->bd_disk) < sb->bucket_size * sb->nbuckets)
 		goto err;
 
-	if (sb->version == CACHE_BACKING_DEV)
+	if (SB_IS_BDEV(sb))
 		goto out;
 
 	err = "Bad UUID";

@@ -286,7 +286,7 @@ void bcache_write_super(struct cache_set *c)
 	for_each_cache(ca, c, i) {
 		struct bio *bio = &ca->sb_bio;
 
-		ca->sb.version		= BCACHE_SB_VERSION;
+		ca->sb.version		= BCACHE_SB_VERSION_CDEV_WITH_UUID;
 		ca->sb.seq		= c->sb.seq;
 		ca->sb.last_mount	= c->sb.last_mount;
 

@@ -1047,9 +1047,20 @@ static const char *register_bdev(struct cache_sb *sb, struct page *sb_page,
 	dc->bdev = bdev;
 	dc->bdev->bd_holder = dc;
 
+	err = "bad start sector";
+	if (sb->version == BCACHE_SB_VERSION_BDEV) {
+		dc->data_start_sector = BDEV_DATA_START_DEFAULT;
+	} else {
+		if (sb->keys < 1)
+			goto err;
+		dc->data_start_sector = sb->d[0];
+		if (dc->data_start_sector < BDEV_DATA_START_DEFAULT)
+			goto err;
+	}
+
 	g = dc->disk.disk;
 
-	set_capacity(g, dc->bdev->bd_part->nr_sects - 16);
+	set_capacity(g, dc->bdev->bd_part->nr_sects - dc->data_start_sector);
 
 	bch_cached_dev_request_init(dc);
 

@@ -1802,7 +1813,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	if (err)
 		goto err_close;
 
-	if (sb->version == CACHE_BACKING_DEV) {
+	if (SB_IS_BDEV(sb)) {
 		struct cached_dev *dc = kzalloc(sizeof(*dc), GFP_KERNEL);
 
 		err = register_bdev(sb, sb_page, bdev, dc);

Signature · 1 line

1.8.2.rc3.7.g35aca0e

Quoted 1 line · Gabriel

Add a new superblock version, and consolidate related defines.

So, I think BDEV_WITH_OFFSET looks ok, but what's the use case for it? I was going to add it way back but we decided not to implement the hack we thought we needed it for - if you or someone is going to use it I'll go ahead and apply it.

As for BCACHE_SB_VERSION_CDEV_WITH_UUID, can you explain why you added that? I suspect it's needed but I can't remember why I didn't add it when I added the new UUID format (or perhaps I just forgot)

Quoted 3 lines

As for BCACHE_SB_VERSION_CDEV_WITH_UUID, can you explain why you added that? I suspect it's needed but I can't remember why I didn't add it when I added the new UUID format (or perhaps I just forgot)

I took the name from a comment in the kernel-side bcache.h. BCACHE_SB_VERSION_CDEV is the version make-bcache writes, and BCACHE_SB_VERSION_CDEV_WITH_UUID is what the kernel updates it too; I just changed the version names so that user-side and kernel-side were more consistent, internally and with each other.
The kernel doesn't discriminate these two versions when opening, so it should be possible to define only the latter and deprecate the other.