xfs: support in-memory btrees

Adapt the generic btree cursor code to be able to create a btree whose
buffers come from a (presumably in-memory) buftarg with a header block
that's specific to in-memory btrees.  We'll connect this to other parts
of online scrub in the next patches.

Note that in-memory btrees always have a block size matching the system
memory page size for efficiency reasons.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/fs/xfs/scrub/xfbtree.h b/fs/xfs/scrub/xfbtree.h
new file mode 100644
index 000000000000..b3836f21085d
--- /dev/null
+++ b/fs/xfs/scrub/xfbtree.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#ifndef XFS_SCRUB_XFBTREE_H__
+#define XFS_SCRUB_XFBTREE_H__
+
+#ifdef CONFIG_XFS_IN_MEMORY_BTREE
+
+/* Root block for an in-memory btree. */
+struct xfs_btree_mem_head {
+	__be32				mh_magic;
+	__be32				mh_nlevels;
+	__be64				mh_owner;
+	__be64				mh_root;
+	uuid_t				mh_uuid;
+};
+
+#define XFS_BTREE_MEM_HEAD_MAGIC	0x4341544D	/* "CATM" */
+
+/* xfile-backed in-memory btrees */
+
+struct xfbtree {
+	/* buffer cache target for this in-memory btree */
+	struct xfs_buftarg		*target;
+
+	/* Owner of this btree. */
+	unsigned long long		owner;
+};
+
+#endif /* CONFIG_XFS_IN_MEMORY_BTREE */
+
+#endif /* XFS_SCRUB_XFBTREE_H__ */