Add a new header that captures the DRBD 9 on-disk metadata layout,
enabling state tracking for multiple peers.
It includes the per-device superblock and per-peer slot structures
needed to track bitmap UUIDs and sync state for each peer.

Co-developed-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
---
 drivers/block/drbd/drbd_meta_data.h | 170 ++++++++++++++++++++++++++++
 1 file changed, 170 insertions(+)
 create mode 100644 drivers/block/drbd/drbd_meta_data.h

diff --git a/drivers/block/drbd/drbd_meta_data.h b/drivers/block/drbd/drbd_meta_data.h
new file mode 100644
index 000000000000..400803267c83
--- /dev/null
+++ b/drivers/block/drbd/drbd_meta_data.h
@@ -0,0 +1,170 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef DRBD_META_DATA_H
+#define DRBD_META_DATA_H
+
+#ifdef __KERNEL__
+#define be_u64 __be64
+#define be_s64 __be64
+#define be_u32 __be32
+#define be_s32 __be32
+#define be_u16 __be16
+#else
+#define be_u64 struct { uint64_t be; }
+#define be_s64 struct { int64_t be; }
+#define be_u32 struct { uint32_t be; }
+#define be_s32 struct { int32_t be; }
+#define be_u16 struct { uint16_t be; }
+#endif
+
+/* how I came up with this magic?
+ * base64 decode "actlog==" ;)
+ */
+#define DRBD_AL_MAGIC 0x69cb65a2
+
+#define BM_BLOCK_SHIFT_4k	12			 /* 4k per bit */
+#define BM_BLOCK_SHIFT_MIN	BM_BLOCK_SHIFT_4k
+#define BM_BLOCK_SHIFT_MAX	20
+#define BM_BLOCK_SIZE_4k	4096
+#define BM_BLOCK_SIZE_MIN	(1<<BM_BLOCK_SHIFT_MIN)
+#define BM_BLOCK_SIZE_MAX	(1<<BM_BLOCK_SHIFT_MAX)
+
+struct peer_dev_md_on_disk_9 {
+	be_u64 bitmap_uuid;
+	be_u64 bitmap_dagtag;
+	be_u32 flags;
+	be_s32 bitmap_index;
+	be_u32 reserved_u32[2];
+} __packed;
+
+/* Changed block tracking: one bitmap slot, not owned by a peer, records every
+ * write to the backing device since the bookmark "id". Valid only with
+ * DRBD_MDFF_CBT in the features.
+ */
+struct cbt_bookmark_on_disk_9 {
+	be_u64 id;		/* the slot records changes since this bookmark */
+	be_u64 bitmap_uuid;	/* current UUID at cbt-start */
+	be_u64 bitmap_dagtag;	/* the Primary's dagtag at cbt-start */
+	be_s64 since;		/* time of cbt-start, seconds since the epoch */
+	be_u32 flags;		/* CBT_BOOKMARK_* */
+	be_s32 bitmap_index;
+} __packed;
+
+struct meta_data_on_disk_9 {
+	be_u64 effective_size;    /* last agreed size */
+	be_u64 current_uuid;
+	be_u64 members;		/* only if MDF_HAVE_MEMBERS_MASK is in the flags */
+	/* Feature flags. Values prefixed with "DRBD_MDFF".
+	 * Separate from "flags": Unknown features bits are cleared; unknown flags bits are kept.
+	 */
+	be_u64 features;
+	be_u64 reserved_u64[2];   /* to have the magic at the same position as in v07, and v08 */
+	be_u64 device_uuid;
+	be_u32 flags;             /* MDF */
+	be_u32 magic;
+	be_u32 md_size_sect;
+	be_u32 al_offset;         /* offset to this block */
+	be_u32 al_nr_extents;     /* important for restoring the AL */
+	be_u32 bm_offset;         /* offset to the bitmap, from here */
+	be_u32 bm_bytes_per_bit;  /* BM_BLOCK_SIZE */
+	be_u32 la_peer_max_bio_size;   /* last peer max_bio_size */
+	be_u32 bm_max_peers;
+	be_s32 node_id;
+
+	/* see al_tr_number_to_on_disk_sector() */
+	be_u32 al_stripes;
+	be_u32 al_stripe_size_4k;
+
+	be_u32 reserved_u32[2];
+
+	struct peer_dev_md_on_disk_9 peers[DRBD_PEERS_MAX];
+	be_u64 history_uuids[HISTORY_UUIDS];
+	struct cbt_bookmark_on_disk_9 cbt_bookmark;
+
+	unsigned char padding_start[0];
+	unsigned char padding_end[0] __attribute__((aligned(4096)));
+} __packed;
+
+/* Attention, these two are defined in drbd_int.h as well! */
+#define AL_UPDATES_PER_TRANSACTION 64
+#define AL_CONTEXT_PER_TRANSACTION 919
+
+enum al_transaction_types {
+	AL_TR_UPDATE = 0,
+	AL_TR_INITIALIZED = 0xffff
+};
+/* all fields on disc in big endian */
+struct __packed al_transaction_on_disk {
+	/* don't we all like magic */
+	be_u32	magic;
+
+	/* to identify the most recent transaction block
+	 * in the on disk ring buffer
+	 */
+	be_u32	tr_number;
+
+	/* checksum on the full 4k block, with this field set to 0. */
+	be_u32	crc32c;
+
+	/* type of transaction, special transaction types like:
+	 * purge-all, set-all-idle, set-all-active, ... to-be-defined
+	 * see also enum al_transaction_types
+	 */
+	be_u16	transaction_type;
+
+	/* we currently allow only a few thousand extents,
+	 * so 16bit will be enough for the slot number.
+	 */
+
+	/* how many updates in this transaction */
+	be_u16	n_updates;
+
+	/* maximum slot number, "al-extents" in drbd.conf speak.
+	 * Having this in each transaction should make reconfiguration
+	 * of that parameter easier.
+	 */
+	be_u16	context_size;
+
+	/* slot number the context starts with */
+	be_u16	context_start_slot_nr;
+
+	/* Some reserved bytes.  Expected usage is a 64bit counter of
+	 * sectors-written since device creation, and other data generation tag
+	 * supporting usage
+	 */
+	be_u32	__reserved[4];
+
+	/* --- 36 byte used --- */
+
+	/* Reserve space for up to AL_UPDATES_PER_TRANSACTION changes
+	 * in one transaction, then use the remaining byte in the 4k block for
+	 * context information.  "Flexible" number of updates per transaction
+	 * does not help, as we have to account for the case when all update
+	 * slots are used anyways, so it would only complicate code without
+	 * additional benefit.
+	 */
+	be_u16	update_slot_nr[AL_UPDATES_PER_TRANSACTION];
+
+	/* but the extent number is 32bit, which at an extent size of 4 MiB
+	 * allows to cover device sizes of up to 2**54 Byte (16 PiB)
+	 */
+	be_u32	update_extent_nr[AL_UPDATES_PER_TRANSACTION];
+
+	/* --- 420 bytes used (36 + 64*6) --- */
+
+	/* 4096 - 420 = 3676 = 919 * 4 */
+	be_u32	context[AL_CONTEXT_PER_TRANSACTION];
+};
+
+#define DRBD_AL_PMEM_MAGIC 0x6aa667a6 /* "al==pmem" */
+
+struct __packed al_on_pmem {
+	be_u32 magic;
+	be_u32 slots[];
+};
+
+#undef be_u64
+#undef be_u32
+#undef be_s32
+#undef be_u16
+
+#endif
-- 
2.56.0