xfs: swap extents operations for CRC filesystems

For CRC enabled filesystems, we can't just swap inode forks from one
inode to another when defragmenting a file - the blocks in the inode
fork bmap btree contain pointers back to the owner inode. Hence if
we are to swap the inode forks we have to atomically modify every
block in the btree during the transaction.

We are doing an entire fork swap here, so we could create a new
transaction item type that indicates we are changing the owner of a
certain structure from one value to another. If we combine this with
ordered buffer logging to modify all the buffers in the tree, then
we can change the buffers in the tree without needing log space for
the operation. However, this then requires log recovery to perform
the modification of the owner information of the objects/structures
in question.

This does introduce some interesting ordering details into recovery:
we have to make sure that the owner change replay occurs after the
change that moves the objects is made, not before. Hence we can't
use a separate log item for this as we have no guarantee of strict
ordering between multiple items in the log due to the relogging
action of asynchronous transaction commits. Hence there is no
"generic" method we can use for changing the ownership of arbitrary
metadata structures.

For inode forks, however, there is a simple method of communicating
that the fork contents need the owner rewritten - we can pass a
inode log format flag for the fork for the transaction that does a
fork swap. This flag will then follow the inode fork through
relogging actions so when the swap actually gets replayed the
ownership can be changed immediately by log recovery.  So that gives
us a simple method of "whole fork" exchange between two inodes.

This is relatively simple to implement, so it makes sense to do this
as an initial implementation to support xfs_fsr on CRC enabled
filesytems in the same manner as we do on existing filesystems. This
commit introduces the swapext driven functionality, the recovery
functionality will be in a separate patch.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 38 insertions, 14 deletions

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 541d59f5e658..ad8a91d2e011 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1789,14 +1789,6 @@ xfs_swap_extents(
 	int		taforkblks = 0;
 	__uint64_t	tmp;
 
-	/*
-	 * We have no way of updating owner information in the BMBT blocks for
-	 * each inode on CRC enabled filesystems, so to avoid corrupting the
-	 * this metadata we simply don't allow extent swaps to occur.
-	 */
-	if (xfs_sb_version_hascrc(&mp->m_sb))
-		return XFS_ERROR(EINVAL);
-
 	tempifp = kmem_alloc(sizeof(xfs_ifork_t), KM_MAYFAIL);
 	if (!tempifp) {
 		error = XFS_ERROR(ENOMEM);
@@ -1920,6 +1912,40 @@ xfs_swap_extents(
 			goto out_trans_cancel;
 	}
 
+	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL | XFS_IOLOCK_EXCL);
+	xfs_trans_ijoin(tp, tip, XFS_ILOCK_EXCL | XFS_IOLOCK_EXCL);
+
+	/*
+	 * Before we've swapped the forks, lets set the owners of the forks
+	 * appropriately. We have to do this as we are demand paging the btree
+	 * buffers, and so the validation done on read will expect the owner
+	 * field to be correctly set. Once we change the owners, we can swap the
+	 * inode forks.
+	 *
+	 * Note the trickiness in setting the log flags - we set the owner log
+	 * flag on the opposite inode (i.e. the inode we are setting the new
+	 * owner to be) because once we swap the forks and log that, log
+	 * recovery is going to see the fork as owned by the swapped inode,
+	 * not the pre-swapped inodes.
+	 */
+	src_log_flags = XFS_ILOG_CORE;
+	target_log_flags = XFS_ILOG_CORE;
+	if (ip->i_d.di_version == 3 &&
+	    ip->i_d.di_format == XFS_DINODE_FMT_BTREE) {
+		target_log_flags |= XFS_ILOG_OWNER;
+		error = xfs_bmbt_change_owner(tp, ip, XFS_DATA_FORK, tip->i_ino);
+		if (error)
+			goto out_trans_cancel;
+	}
+
+	if (tip->i_d.di_version == 3 &&
+	    tip->i_d.di_format == XFS_DINODE_FMT_BTREE) {
+		src_log_flags |= XFS_ILOG_OWNER;
+		error = xfs_bmbt_change_owner(tp, tip, XFS_DATA_FORK, ip->i_ino);
+		if (error)
+			goto out_trans_cancel;
+	}
+
 	/*
 	 * Swap the data forks of the inodes
 	 */
@@ -1957,7 +1983,6 @@ xfs_swap_extents(
 	tip->i_delayed_blks = ip->i_delayed_blks;
 	ip->i_delayed_blks = 0;
 
-	src_log_flags = XFS_ILOG_CORE;
 	switch (ip->i_d.di_format) {
 	case XFS_DINODE_FMT_EXTENTS:
 		/* If the extents fit in the inode, fix the
@@ -1971,11 +1996,12 @@ xfs_swap_extents(
 		src_log_flags |= XFS_ILOG_DEXT;
 		break;
 	case XFS_DINODE_FMT_BTREE:
+		ASSERT(ip->i_d.di_version < 3 ||
+		       (src_log_flags & XFS_ILOG_OWNER));
 		src_log_flags |= XFS_ILOG_DBROOT;
 		break;
 	}
 
-	target_log_flags = XFS_ILOG_CORE;
 	switch (tip->i_d.di_format) {
 	case XFS_DINODE_FMT_EXTENTS:
 		/* If the extents fit in the inode, fix the
@@ -1990,13 +2016,11 @@ xfs_swap_extents(
 		break;
 	case XFS_DINODE_FMT_BTREE:
 		target_log_flags |= XFS_ILOG_DBROOT;
+		ASSERT(tip->i_d.di_version < 3 ||
+		       (target_log_flags & XFS_ILOG_OWNER));
 		break;
 	}
 
-
-	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL | XFS_IOLOCK_EXCL);
-	xfs_trans_ijoin(tp, tip, XFS_ILOCK_EXCL | XFS_IOLOCK_EXCL);
-
 	xfs_trans_log_inode(tp, ip,  src_log_flags);
 	xfs_trans_log_inode(tp, tip, target_log_flags);