xfs: split direct I/O and DAX path

So far the DAX code overloaded the direct I/O code path.  There is very little
in common between the two, and untangling them allows to clean up both variants.

As a side effect we also get separate trace points for both I/O types.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_file.c

@@ -305,14 +305,12 @@ xfs_file_dio_aio_read(
 	else
 		target = ip->i_mount->m_ddev_targp;
 
-	if (!IS_DAX(inode)) {
 	/* DIO must be aligned to device logical sector size */
 	if ((iocb->ki_pos | count) & target->bt_logical_sectormask) {
 		if (iocb->ki_pos == isize)
 			return 0;
 		return -EINVAL;
 	}
-	}
 
 	/*
 	 * Locking is a bit tricky here. If we take an exclusive lock for direct
@@ -360,13 +358,37 @@ xfs_file_dio_aio_read(
 	}
 
 	data = *to;
-	if (IS_DAX(inode)) {
-		ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct,
-				NULL, 0);
-	} else {
 	ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
 			xfs_get_blocks_direct, NULL, NULL, 0);
+	if (ret > 0) {
+		iocb->ki_pos += ret;
+		iov_iter_advance(to, ret);
 	}
+	xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
+
+	file_accessed(iocb->ki_filp);
+	return ret;
+}
+
+STATIC ssize_t
+xfs_file_dax_read(
+	struct kiocb		*iocb,
+	struct iov_iter		*to)
+{
+	struct address_space	*mapping = iocb->ki_filp->f_mapping;
+	struct inode		*inode = mapping->host;
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct iov_iter		data = *to;
+	size_t			count = iov_iter_count(to);
+	ssize_t			ret = 0;
+
+	trace_xfs_file_dax_read(ip, count, iocb->ki_pos);
+
+	if (!count)
+		return 0; /* skip atime */
+
+	xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
+	ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct, NULL, 0);
 	if (ret > 0) {
 		iocb->ki_pos += ret;
 		iov_iter_advance(to, ret);
@@ -399,7 +421,8 @@ xfs_file_read_iter(
 	struct kiocb		*iocb,
 	struct iov_iter		*to)
 {
-	struct xfs_mount	*mp = XFS_I(file_inode(iocb->ki_filp))->i_mount;
+	struct inode		*inode = file_inode(iocb->ki_filp);
+	struct xfs_mount	*mp = XFS_I(inode)->i_mount;
 	ssize_t			ret = 0;
 
 	XFS_STATS_INC(mp, xs_read_calls);
@@ -407,7 +430,9 @@ xfs_file_read_iter(
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return -EIO;
 
-	if (iocb->ki_flags & IOCB_DIRECT)
+	if (IS_DAX(inode))
+		ret = xfs_file_dax_read(iocb, to);
+	else if (iocb->ki_flags & IOCB_DIRECT)
 		ret = xfs_file_dio_aio_read(iocb, to);
 	else
 		ret = xfs_file_buffered_aio_read(iocb, to);
@@ -755,8 +780,7 @@ xfs_file_dio_aio_write(
 					mp->m_rtdev_targp : mp->m_ddev_targp;
 
 	/* DIO must be aligned to device logical sector size */
-	if (!IS_DAX(inode) &&
-	    ((iocb->ki_pos | count) & target->bt_logical_sectormask))
+	if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
 		return -EINVAL;
 
 	/* "unaligned" here means not aligned to a filesystem block */
@@ -825,14 +849,9 @@ xfs_file_dio_aio_write(
 	trace_xfs_file_direct_write(ip, count, iocb->ki_pos);
 
 	data = *from;
-	if (IS_DAX(inode)) {
-		ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct,
-				xfs_end_io_direct_write, 0);
-	} else {
 	ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
 			xfs_get_blocks_direct, xfs_end_io_direct_write,
 			NULL, DIO_ASYNC_EXTEND);
-	}
 
 	/* see generic_file_direct_write() for why this is necessary */
 	if (mapping->nrpages) {
@@ -849,10 +868,70 @@ xfs_file_dio_aio_write(
 	xfs_rw_iunlock(ip, iolock);
 
 	/*
-	 * No fallback to buffered IO on errors for XFS. DAX can result in
-	 * partial writes, but direct IO will either complete fully or fail.
+	 * No fallback to buffered IO on errors for XFS, direct IO will either
+	 * complete fully or fail.
+	 */
+	ASSERT(ret < 0 || ret == count);
+	return ret;
+}
+
+STATIC ssize_t
+xfs_file_dax_write(
+	struct kiocb		*iocb,
+	struct iov_iter		*from)
+{
+	struct address_space	*mapping = iocb->ki_filp->f_mapping;
+	struct inode		*inode = mapping->host;
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
+	ssize_t			ret = 0;
+	int			unaligned_io = 0;
+	int			iolock;
+	struct iov_iter		data;
+
+	/* "unaligned" here means not aligned to a filesystem block */
+	if ((iocb->ki_pos & mp->m_blockmask) ||
+	    ((iocb->ki_pos + iov_iter_count(from)) & mp->m_blockmask)) {
+		unaligned_io = 1;
+		iolock = XFS_IOLOCK_EXCL;
+	} else if (mapping->nrpages) {
+		iolock = XFS_IOLOCK_EXCL;
+	} else {
+		iolock = XFS_IOLOCK_SHARED;
+	}
+	xfs_rw_ilock(ip, iolock);
+
+	ret = xfs_file_aio_write_checks(iocb, from, &iolock);
+	if (ret)
+		goto out;
+
+	/*
+	 * Yes, even DAX files can have page cache attached to them:  A zeroed
+	 * page is inserted into the pagecache when we have to serve a write
+	 * fault on a hole.  It should never be dirtied and can simply be
+	 * dropped from the pagecache once we get real data for the page.
 	 */
-	ASSERT(ret < 0 || ret == count || IS_DAX(VFS_I(ip)));
+	if (mapping->nrpages) {
+		ret = invalidate_inode_pages2(mapping);
+		WARN_ON_ONCE(ret);
+	}
+
+	if (iolock == XFS_IOLOCK_EXCL && !unaligned_io) {
+		xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
+		iolock = XFS_IOLOCK_SHARED;
+	}
+
+	trace_xfs_file_dax_write(ip, iov_iter_count(from), iocb->ki_pos);
+
+	data = *from;
+	ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct,
+			xfs_end_io_direct_write, 0);
+	if (ret > 0) {
+		iocb->ki_pos += ret;
+		iov_iter_advance(from, ret);
+	}
+out:
+	xfs_rw_iunlock(ip, iolock);
 	return ret;
 }
 
@@ -934,7 +1013,9 @@ xfs_file_write_iter(
 	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
 		return -EIO;
 
-	if ((iocb->ki_flags & IOCB_DIRECT) || IS_DAX(inode))
+	if (IS_DAX(inode))
+		ret = xfs_file_dax_write(iocb, from);
+	else if (iocb->ki_flags & IOCB_DIRECT)
 		ret = xfs_file_dio_aio_write(iocb, from);
 	else
 		ret = xfs_file_buffered_aio_write(iocb, from);

fs/xfs/xfs_trace.h

@@ -1164,8 +1164,10 @@ DEFINE_EVENT(xfs_file_class, name,	\
 	TP_ARGS(ip, count, offset))
 DEFINE_RW_EVENT(xfs_file_buffered_read);
 DEFINE_RW_EVENT(xfs_file_direct_read);
+DEFINE_RW_EVENT(xfs_file_dax_read);
 DEFINE_RW_EVENT(xfs_file_buffered_write);
 DEFINE_RW_EVENT(xfs_file_direct_write);
+DEFINE_RW_EVENT(xfs_file_dax_write);
 DEFINE_RW_EVENT(xfs_file_splice_read);
 
 DECLARE_EVENT_CLASS(xfs_page_class,