xfs: introduce new file range commit ioctls

Source kernel commit: 398597c3ef7fb1d8fa31491c8f4f3996cff45701

This patch introduces two more new ioctls to manage atomic updates to
file contents -- XFS_IOC_START_COMMIT and XFS_IOC_COMMIT_RANGE.  The
does, but with the additional requirement that file2 cannot have changed
since some sampling point.  The start-commit ioctl performs the sampling
of file attributes.

Note: This patch currently samples i_ctime during START_COMMIT and
checks that it hasn't changed during COMMIT_RANGE.  This isn't entirely
safe in kernels prior to 6.12 because ctime only had coarse grained
granularity and very fast updates could collide with a COMMIT_RANGE.
With the multi-granularity ctime introduced by Jeff Layton, it's now
possible to update ctime such that this does not happen.

It is critical, then, that this patch must not be backported to any
kernel that does not support fine-grained file change timestamps.

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

diff --git a/libxfs/xfs_fs.h b/libxfs/xfs_fs.h
index 184ccbfe7082180134e5fdeccd405b9bfb860dee..860284064c5aa9304d045b3e9ebfcf346e9fd968 100644 (file)
--- a/libxfs/xfs_fs.h
+++ b/libxfs/xfs_fs.h
@@ -826,6 +826,30 @@ struct xfs_exchange_range {
        __u64           flags;          /* see XFS_EXCHANGE_RANGE_* below */
 };
 
+/*
+ * Using the same definition of file2 as struct xfs_exchange_range, commit the
+ * contents of file1 into file2 if file2 has the same inode number, mtime, and
+ * ctime as the arguments provided to the call.  The old contents of file2 will
+ * be moved to file1.
+ *
+ * Returns -EBUSY if there isn't an exact match for the file2 fields.
+ *
+ * Filesystems must be able to restart and complete the operation even after
+ * the system goes down.
+ */
+struct xfs_commit_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 */
+
+       /* opaque file2 metadata for freshness checks */
+       __u64           file2_freshness[6];
+};
+
 /*
  * 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
@@ -998,6 +1022,8 @@ struct xfs_getparents_by_handle {
 #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      _IOW ('X', 129, struct xfs_exchange_range)
+#define XFS_IOC_START_COMMIT        _IOR ('X', 130, struct xfs_commit_range)
+#define XFS_IOC_COMMIT_RANGE        _IOW ('X', 131, struct xfs_commit_range)
 /*     XFS_IOC_GETFSUUID ---------- deprecated 140      */