[PATCH 1/1] xfs: use reflink to assist unaligned copy_file_range calls

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

Add a copy_file_range handler to XFS so that we can accelerate file
copies with reflink when the source and destination ranges are not
block-aligned.  We'll use the generic pagecache copy to handle the
unaligned edges and attempt to reflink the middle.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/xfs_file.c |   99 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)


diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 5b0f93f73837..9d1bb0dc30e2 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1119,6 +1119,104 @@ xfs_file_remap_range(
 	return remapped > 0 ? remapped : ret;
 }
 
+/*
+ * Decide if we want to use reflink to accelerate a copy_file_range request.
+ *
+ * We need to use the generic pagecache copy routine if there's no reflink; if
+ * the two files are on different filesystems; if the two files are on
+ * different devices; or if the two offsets are not at the same offset within
+ * an fs block.  Studies on the author's computer show that reflink doesn't
+ * speed up copies smaller than 32k, so use the page cache for those.
+ */
+static inline bool
+xfs_want_reflink_copy_range(
+	struct xfs_inode	*src,
+	unsigned int		src_off,
+	struct xfs_inode	*dst,
+	unsigned int		dst_off,
+	size_t			len)
+{
+	struct xfs_mount	*mp = src->i_mount;
+
+	if (len < 32768)
+		return false;
+	if (mp != dst->i_mount)
+		return false;
+	if (!xfs_sb_version_hasreflink(&mp->m_sb))
+		return false;
+	if (XFS_IS_REALTIME_INODE(src) != XFS_IS_REALTIME_INODE(dst))
+		return false;
+	return (src_off & mp->m_blockmask) == (dst_off & mp->m_blockmask);
+}
+
+STATIC ssize_t
+xfs_file_copy_range(
+	struct file		*src_file,
+	loff_t			src_off,
+	struct file		*dst_file,
+	loff_t			dst_off,
+	size_t			len,
+	unsigned int		flags)
+{
+	struct inode		*inode_src = file_inode(src_file);
+	struct xfs_inode	*src = XFS_I(inode_src);
+	struct inode		*inode_dst = file_inode(dst_file);
+	struct xfs_inode	*dst = XFS_I(inode_dst);
+	struct xfs_mount	*mp = src->i_mount;
+	loff_t			copy_ret;
+	loff_t			next_block;
+	size_t			copy_len;
+	ssize_t			total_copied = 0;
+
+	/* Bypass all this if no copy acceleration is possible. */
+	if (!xfs_want_reflink_copy_range(src, src_off, dst, dst_off, len))
+		goto use_generic;
+
+	/* Use the regular copy until we're block aligned at the start. */
+	next_block = round_up(src_off + 1, mp->m_sb.sb_blocksize);
+	copy_len = min_t(size_t, len, next_block - src_off);
+	if (copy_len > 0) {
+		copy_ret = generic_copy_file_range(src_file, src_off, dst_file,
+					dst_off, copy_len, flags);
+		if (copy_ret < 0)
+			return copy_ret;
+
+		src_off += copy_ret;
+		dst_off += copy_ret;
+		len -= copy_ret;
+		total_copied += copy_ret;
+		if (copy_ret < copy_len || len == 0)
+			return total_copied;
+	}
+
+	/*
+	 * Now try to reflink as many full blocks as we can.  If the end of the
+	 * copy request wasn't block-aligned or the reflink fails, we'll just
+	 * fall into the generic copy to do the rest.
+	 */
+	copy_len = round_down(len, mp->m_sb.sb_blocksize);
+	if (copy_len > 0) {
+		copy_ret = xfs_file_remap_range(src_file, src_off, dst_file,
+				dst_off, copy_len, REMAP_FILE_CAN_SHORTEN);
+		if (copy_ret >= 0) {
+			src_off += copy_ret;
+			dst_off += copy_ret;
+			len -= copy_ret;
+			total_copied += copy_ret;
+			if (copy_ret < copy_len || len == 0)
+				return total_copied;
+		}
+	}
+
+use_generic:
+	/* Use the regular copy to deal with leftover bytes. */
+	copy_ret = generic_copy_file_range(src_file, src_off, dst_file,
+			dst_off, len, flags);
+	if (copy_ret < 0)
+		return copy_ret;
+	return total_copied + copy_ret;
+}
+
 STATIC int
 xfs_file_open(
 	struct inode	*inode,
@@ -1381,6 +1479,7 @@ const struct file_operations xfs_file_operations = {
 	.get_unmapped_area = thp_get_unmapped_area,
 	.fallocate	= xfs_file_fallocate,
 	.fadvise	= xfs_file_fadvise,
+	.copy_file_range = xfs_file_copy_range,
 	.remap_file_range = xfs_file_remap_range,
 };