xfs: introduce new file range exchange ioctl

Introduce a new ioctl to handle exchanging ranges of bytes
between files.  The goal here is to perform the exchange atomically with
respect to applications -- either they see the file contents before the
exchange or they see that A-B is now B-A, even if the kernel crashes.

My original goal with all this code was to make it so that online repair
can build a replacement directory or xattr structure in a temporary file
and commit the repair by atomically exchanging all the data blocks
between the two files.  However, I needed a way to test this mechanism
thoroughly, so I've been evolving an ioctl interface since then.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 1397edea20f1..efa95892655d 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -40,6 +40,7 @@
 #include "xfs_xattr.h"
 #include "xfs_rtbitmap.h"
 #include "xfs_file.h"
+#include "xfs_exchrange.h"
 
 #include <linux/mount.h>
 #include <linux/namei.h>
@@ -2170,6 +2171,9 @@ xfs_file_ioctl(
 		return error;
 	}
 
+	case XFS_IOC_EXCHANGE_RANGE:
+		return xfs_ioc_exchange_range(filp, arg);
+
 	default:
 		return -ENOTTY;
 	}