From: Darrick J. Wong <djwong@xxxxxxxxxx>
Source kernel commit: 9a64d9b3109d01cca0b83c1d36538b7a37c5284e
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@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
libxfs/xfs_fs.h | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/libxfs/xfs_fs.h b/libxfs/xfs_fs.h
index ca1b17d01..8a1e30cf4 100644
--- a/libxfs/xfs_fs.h
+++ b/libxfs/xfs_fs.h
@@ -772,6 +772,46 @@ struct xfs_scrub_metadata {
# define XFS_XATTR_LIST_MAX 65536
#endif
+/*
+ * Exchange part of file1 with part of the file that this ioctl that is being
+ * called against (which we'll call file2). Filesystems must be able to
+ * restart and complete the operation even after the system goes down.
+ */
+struct xfs_exchange_range {
+ __s32 file1_fd;
+ __u32 pad; /* must be zeroes */
+ __u64 file1_offset; /* file1 offset, bytes */
+ __u64 file2_offset; /* file2 offset, bytes */
+ __u64 length; /* bytes to exchange */
+
+ __u64 flags; /* see XFS_EXCHANGE_RANGE_* below */
+};
+
+/*
+ * Exchange file data all the way to the ends of both files, and then exchange
+ * the file sizes. This flag can be used to replace a file's contents with a
+ * different amount of data. length will be ignored.
+ */
+#define XFS_EXCHANGE_RANGE_TO_EOF (1ULL << 0)
+
+/* Flush all changes in file data and file metadata to disk before returning. */
+#define XFS_EXCHANGE_RANGE_DSYNC (1ULL << 1)
+
+/* Dry run; do all the parameter verification but do not change anything. */
+#define XFS_EXCHANGE_RANGE_DRY_RUN (1ULL << 2)
+
+/*
+ * Exchange only the parts of the two files where the file allocation units
+ * mapped to file1's range have been written to. This can accelerate
+ * scatter-gather atomic writes with a temp file if all writes are aligned to
+ * the file allocation unit.
+ */
+#define XFS_EXCHANGE_RANGE_FILE1_WRITTEN (1ULL << 3)
+
+#define XFS_EXCHANGE_RANGE_ALL_FLAGS (XFS_EXCHANGE_RANGE_TO_EOF | \
+ XFS_EXCHANGE_RANGE_DSYNC | \
+ XFS_EXCHANGE_RANGE_DRY_RUN | \
+ XFS_EXCHANGE_RANGE_FILE1_WRITTEN)
/*
* ioctl commands that are used by Linux filesystems
@@ -843,6 +883,7 @@ struct xfs_scrub_metadata {
#define XFS_IOC_FSGEOMETRY _IOR ('X', 126, struct xfs_fsop_geom)
#define XFS_IOC_BULKSTAT _IOR ('X', 127, struct xfs_bulkstat_req)
#define XFS_IOC_INUMBERS _IOR ('X', 128, struct xfs_inumbers_req)
+#define XFS_IOC_EXCHANGE_RANGE _IOWR('X', 129, struct xfs_exchange_range)
/* XFS_IOC_GETFSUUID ---------- deprecated 140 */
