drbd: prepare for new striped layout of activity log

Introduce two new on-disk meta data fields: al_stripes and al_stripe_size_4k
The intended use case is activity log on RAID 0 or similar.
Logically consecutive transactions will advance their on-disk position
by al_stripe_size_4k 4kB (transaction sized) blocks.

Right now, these are still asserted to be the backward compatible
values al_stripes = 1, al_stripe_size_4k = 8 (which amounts to 32kB).

Also introduce a caching member for meta_dev_idx in the in-core
structure: even though it is initially passed in in the rcu-protected
disk_conf structure, it cannot change without a detach/attach cycle.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 20 insertions, 26 deletions

diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 60c89e5b298c..ee19ba28b59a 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -755,6 +755,14 @@ struct drbd_md {
 
 	s32 al_offset;	/* signed relative sector offset to activity log */
 	s32 bm_offset;	/* signed relative sector offset to bitmap */
+
+	/* cached value of bdev->disk_conf->meta_dev_idx (see below) */
+	s32 meta_dev_idx;
+
+	/* see al_tr_number_to_on_disk_sector() */
+	u32 al_stripes;
+	u32 al_stripe_size_4k;
+	u32 al_size_4k; /* cached product of the above */
 };
 
 struct drbd_backing_dev {
@@ -1862,38 +1870,24 @@ static inline sector_t drbd_get_max_capacity(struct drbd_backing_dev *bdev)
 }
 
 /**
- * drbd_md_ss__() - Return the sector number of our meta data super block
- * @mdev:	DRBD device.
+ * drbd_md_ss() - Return the sector number of our meta data super block
  * @bdev:	Meta data block device.
  */
-static inline sector_t drbd_md_ss__(struct drbd_conf *mdev,
-				    struct drbd_backing_dev *bdev)
+static inline sector_t drbd_md_ss(struct drbd_backing_dev *bdev)
 {
-	int meta_dev_idx;
+	const int meta_dev_idx = bdev->md.meta_dev_idx;
 
-	rcu_read_lock();
-	meta_dev_idx = rcu_dereference(bdev->disk_conf)->meta_dev_idx;
-	rcu_read_unlock();
+	if (meta_dev_idx == DRBD_MD_INDEX_FLEX_EXT)
+		return 0;
 
-	switch (meta_dev_idx) {
-	default: /* external, some index; this is the old fixed size layout */
-		return MD_128MB_SECT * meta_dev_idx;
-	case DRBD_MD_INDEX_INTERNAL:
-		/* with drbd08, internal meta data is always "flexible" */
-	case DRBD_MD_INDEX_FLEX_INT:
-		if (!bdev->backing_bdev) {
-			if (__ratelimit(&drbd_ratelimit_state)) {
-				dev_err(DEV, "bdev->backing_bdev==NULL\n");
-				dump_stack();
-			}
-			return 0;
-		}
-		/* sizeof(struct md_on_disk_07) == 4k
-		 * position: last 4k aligned block of 4k size */
+	/* Since drbd08, internal meta data is always "flexible".
+	 * position: last 4k aligned block of 4k size */
+	if (meta_dev_idx == DRBD_MD_INDEX_INTERNAL ||
+	    meta_dev_idx == DRBD_MD_INDEX_FLEX_INT)
 		return (drbd_get_capacity(bdev->backing_bdev) & ~7ULL) - 8;
-	case DRBD_MD_INDEX_FLEX_EXT:
-		return 0;
-	}
+
+	/* external, some index; this is the old fixed size layout */
+	return MD_128MB_SECT * bdev->md.meta_dev_idx;
 }
 
 static inline void