drbd: cleanup ondisk meta data layout calculations and defines
Add a comment about our meta data layout variants,
and rename a few defines (e.g. MD_RESERVED_SECT -> MD_128MB_SECT)
to make it clear that they are short hand for fixed constants,
and not arbitrarily to be redefined as one may see fit.
Properly pad struct meta_data_on_disk to 4kB,
and initialize to zero not only the first 512 Byte,
but all of it in drbd_md_sync().
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>
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index db504d0..60c89e5 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -753,13 +753,8 @@
u32 flags;
u32 md_size_sect;
- s32 al_offset; /* signed relative sector offset to al area */
+ s32 al_offset; /* signed relative sector offset to activity log */
s32 bm_offset; /* signed relative sector offset to bitmap */
-
- /* u32 al_nr_extents; important for restoring the AL
- * is stored into ldev->dc.al_extents, which in turn
- * gets applied to act_log->nr_elements
- */
};
struct drbd_backing_dev {
@@ -1009,7 +1004,6 @@
struct lru_cache *act_log; /* activity log */
unsigned int al_tr_number;
int al_tr_cycle;
- int al_tr_pos; /* position of the next transaction in the journal */
wait_queue_head_t seq_wait;
atomic_t packet_seq;
unsigned int peer_seq;
@@ -1151,21 +1145,41 @@
extern void drbd_ldev_destroy(struct drbd_conf *mdev);
/* Meta data layout
- We reserve a 128MB Block (4k aligned)
- * either at the end of the backing device
- * or on a separate meta data device. */
+ *
+ * We currently have two possible layouts.
+ * Offsets in (512 byte) sectors.
+ * external:
+ * |----------- md_size_sect ------------------|
+ * [ 4k superblock ][ activity log ][ Bitmap ]
+ * | al_offset == 8 |
+ * | bm_offset = al_offset + X |
+ * ==> bitmap sectors = md_size_sect - bm_offset
+ *
+ * Variants:
+ * old, indexed fixed size meta data:
+ *
+ * internal:
+ * |----------- md_size_sect ------------------|
+ * [data.....][ Bitmap ][ activity log ][ 4k superblock ][padding*]
+ * | al_offset < 0 |
+ * | bm_offset = al_offset - Y |
+ * ==> bitmap sectors = Y = al_offset - bm_offset
+ *
+ * [padding*] are zero or up to 7 unused 512 Byte sectors to the
+ * end of the device, so that the [4k superblock] will be 4k aligned.
+ *
+ * The activity log consists of 4k transaction blocks,
+ * which are written in a ring-buffer, or striped ring-buffer like fashion,
+ * which are writtensize used to be fixed 32kB,
+ * but is about to become configurable.
+ */
-/* The following numbers are sectors */
-/* Allows up to about 3.8TB, so if you want more,
+/* Our old fixed size meta data layout
+ * allows up to about 3.8TB, so if you want more,
* you need to use the "flexible" meta data format. */
-#define MD_RESERVED_SECT (128LU << 11) /* 128 MB, unit sectors */
-#define MD_AL_OFFSET 8 /* 8 Sectors after start of meta area */
-#define MD_AL_SECTORS 64 /* = 32 kB on disk activity log ring buffer */
-#define MD_BM_OFFSET (MD_AL_OFFSET + MD_AL_SECTORS)
-
-/* we do all meta data IO in 4k blocks */
-#define MD_BLOCK_SHIFT 12
-#define MD_BLOCK_SIZE (1<<MD_BLOCK_SHIFT)
+#define MD_128MB_SECT (128LLU << 11) /* 128 MB, unit sectors */
+#define MD_4kB_SECT 8
+#define MD_32kB_SECT 64
/* One activity log extent represents 4M of storage */
#define AL_EXTENT_SHIFT 22
@@ -1255,7 +1269,6 @@
/* in one sector of the bitmap, we have this many activity_log extents. */
#define AL_EXT_PER_BM_SECT (1 << (BM_EXT_SHIFT - AL_EXTENT_SHIFT))
-#define BM_WORDS_PER_AL_EXT (1 << (AL_EXTENT_SHIFT-BM_BLOCK_SHIFT-LN2_BPL))
#define BM_BLOCKS_PER_BM_EXT_B (BM_EXT_SHIFT - BM_BLOCK_SHIFT)
#define BM_BLOCKS_PER_BM_EXT_MASK ((1<<BM_BLOCKS_PER_BM_EXT_B) - 1)
@@ -1275,16 +1288,18 @@
*/
#define DRBD_MAX_SECTORS_32 (0xffffffffLU)
-#define DRBD_MAX_SECTORS_BM \
- ((MD_RESERVED_SECT - MD_BM_OFFSET) * (1LL<<(BM_EXT_SHIFT-9)))
-#if DRBD_MAX_SECTORS_BM < DRBD_MAX_SECTORS_32
-#define DRBD_MAX_SECTORS DRBD_MAX_SECTORS_BM
-#define DRBD_MAX_SECTORS_FLEX DRBD_MAX_SECTORS_BM
-#elif !defined(CONFIG_LBDAF) && BITS_PER_LONG == 32
+/* we have a certain meta data variant that has a fixed on-disk size of 128
+ * MiB, of which 4k are our "superblock", and 32k are the fixed size activity
+ * log, leaving this many sectors for the bitmap.
+ */
+
+#define DRBD_MAX_SECTORS_FIXED_BM \
+ ((MD_128MB_SECT - MD_32kB_SECT - MD_4kB_SECT) * (1LL<<(BM_EXT_SHIFT-9)))
+#if !defined(CONFIG_LBDAF) && BITS_PER_LONG == 32
#define DRBD_MAX_SECTORS DRBD_MAX_SECTORS_32
#define DRBD_MAX_SECTORS_FLEX DRBD_MAX_SECTORS_32
#else
-#define DRBD_MAX_SECTORS DRBD_MAX_SECTORS_BM
+#define DRBD_MAX_SECTORS DRBD_MAX_SECTORS_FIXED_BM
/* 16 TB in units of sectors */
#if BITS_PER_LONG == 32
/* adjust by one page worth of bitmap,
@@ -1792,10 +1807,10 @@
switch (meta_dev_idx) {
case DRBD_MD_INDEX_INTERNAL:
case DRBD_MD_INDEX_FLEX_INT:
- return bdev->md.md_offset + MD_AL_OFFSET - 1;
+ return bdev->md.md_offset + MD_4kB_SECT -1;
case DRBD_MD_INDEX_FLEX_EXT:
default:
- return bdev->md.md_offset + bdev->md.md_size_sect;
+ return bdev->md.md_offset + bdev->md.md_size_sect -1;
}
}
@@ -1861,13 +1876,11 @@
rcu_read_unlock();
switch (meta_dev_idx) {
- default: /* external, some index */
- return MD_RESERVED_SECT * 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:
- /* sizeof(struct md_on_disk_07) == 4k
- * position: last 4k aligned block of 4k size */
if (!bdev->backing_bdev) {
if (__ratelimit(&drbd_ratelimit_state)) {
dev_err(DEV, "bdev->backing_bdev==NULL\n");
@@ -1875,8 +1888,9 @@
}
return 0;
}
- return (drbd_get_capacity(bdev->backing_bdev) & ~7ULL)
- - MD_AL_OFFSET;
+ /* sizeof(struct md_on_disk_07) == 4k
+ * position: last 4k aligned block of 4k size */
+ return (drbd_get_capacity(bdev->backing_bdev) & ~7ULL) - 8;
case DRBD_MD_INDEX_FLEX_EXT:
return 0;
}