xfs: introduce a file mapping exchange log intent item

Introduce a new intent log item to handle exchanging mappings between
the forks of two files.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 59 insertions, 0 deletions

diff --git a/fs/xfs/xfs_exchmaps_item.h b/fs/xfs/xfs_exchmaps_item.h
new file mode 100644
index 000000000000..ada1eb314e65
--- /dev/null
+++ b/fs/xfs/xfs_exchmaps_item.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (c) 2020-2024 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#ifndef	__XFS_EXCHMAPS_ITEM_H__
+#define	__XFS_EXCHMAPS_ITEM_H__
+
+/*
+ * The file mapping exchange intent item helps us exchange multiple file
+ * mappings between two inode forks.  It does this by tracking the range of
+ * file block offsets that still need to be exchanged, and relogs as progress
+ * happens.
+ *
+ * *I items should be recorded in the *first* of a series of rolled
+ * transactions, and the *D items should be recorded in the same transaction
+ * that records the associated bmbt updates.
+ *
+ * Should the system crash after the commit of the first transaction but
+ * before the commit of the final transaction in a series, log recovery will
+ * use the redo information recorded by the intent items to replay the
+ * rest of the mapping exchanges.
+ */
+
+/* kernel only XMI/XMD definitions */
+
+struct xfs_mount;
+struct kmem_cache;
+
+/*
+ * This is the incore file mapping exchange intent log item.  It is used to log
+ * the fact that we are exchanging mappings between two files.  It is used in
+ * conjunction with the incore file mapping exchange done log item described
+ * below.
+ *
+ * These log items follow the same rules as struct xfs_efi_log_item; see the
+ * comments about that structure (in xfs_extfree_item.h) for more details.
+ */
+struct xfs_xmi_log_item {
+	struct xfs_log_item		xmi_item;
+	atomic_t			xmi_refcount;
+	struct xfs_xmi_log_format	xmi_format;
+};
+
+/*
+ * This is the incore file mapping exchange done log item.  It is used to log
+ * the fact that an exchange mentioned in an earlier xmi item have been
+ * performed.
+ */
+struct xfs_xmd_log_item {
+	struct xfs_log_item		xmd_item;
+	struct xfs_xmi_log_item		*xmd_intent_log_item;
+	struct xfs_xmd_log_format	xmd_format;
+};
+
+extern struct kmem_cache	*xfs_xmi_cache;
+extern struct kmem_cache	*xfs_xmd_cache;
+
+#endif	/* __XFS_EXCHMAPS_ITEM_H__ */