xfs: split direct IO write path from xfs_file_aio_write

The current xfs_file_aio_write code is a mess of locking shenanigans
to handle the different locking requirements of buffered and direct
IO. Start to clean this up by disentangling the direct IO path from
the mess.

This also removes the failed direct IO fallback path to buffered IO.
XFS handles all direct IO cases without needing to fall back to
buffered IO, so we can safely remove this unused path. This greatly
simplifies the logic and locking needed in the write path.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/linux-2.6/xfs_file.c

@@ -628,6 +628,116 @@ xfs_zero_eof(
 	return error;
 }
 
+/*
+ * xfs_file_dio_aio_write - handle direct IO writes
+ *
+ * Lock the inode appropriately to prepare for and issue a direct IO write.
+ * By spearating it from the buffered write path we remove all the tricky to
+ * follow locking changes and looping.
+ *
+ * Returns with locks held indicated by @iolock and errors indicated by
+ * negative return values.
+ */
+STATIC ssize_t
+xfs_file_dio_aio_write(
+	struct kiocb		*iocb,
+	const struct iovec	*iovp,
+	unsigned long		nr_segs,
+	loff_t			pos,
+	size_t			ocount,
+	int			*iolock)
+{
+	struct file		*file = iocb->ki_filp;
+	struct address_space	*mapping = file->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;
+	xfs_fsize_t		new_size;
+	size_t			count = ocount;
+	struct xfs_buftarg	*target = XFS_IS_REALTIME_INODE(ip) ?
+					mp->m_rtdev_targp : mp->m_ddev_targp;
+
+	*iolock = 0;
+	if ((pos & target->bt_smask) || (count & target->bt_smask))
+		return -XFS_ERROR(EINVAL);
+
+	/*
+	 * For direct I/O, if there are cached pages or we're extending
+	 * the file, we need IOLOCK_EXCL until we're sure the bytes at
+	 * the new EOF have been zeroed and/or the cached pages are
+	 * flushed out.
+	 */
+	if (mapping->nrpages || pos > ip->i_size)
+		*iolock = XFS_IOLOCK_EXCL;
+	else
+		*iolock = XFS_IOLOCK_SHARED;
+	xfs_rw_ilock(ip, XFS_ILOCK_EXCL | *iolock);
+
+	ret = generic_write_checks(file, &pos, &count,
+					S_ISBLK(inode->i_mode));
+	if (ret) {
+		xfs_rw_iunlock(ip, XFS_ILOCK_EXCL | *iolock);
+		*iolock = 0;
+		return ret;
+	}
+
+	new_size = pos + count;
+	if (new_size > ip->i_size)
+		ip->i_new_size = new_size;
+
+	if (likely(!(file->f_mode & FMODE_NOCMTIME)))
+		file_update_time(file);
+
+	/*
+	 * If the offset is beyond the size of the file, we have a couple of
+	 * things to do. First, if there is already space allocated we need to
+	 * either create holes or zero the disk or ...
+	 *
+	 * If there is a page where the previous size lands, we need to zero it
+	 * out up to the new size.
+	 */
+	if (pos > ip->i_size) {
+		ret = -xfs_zero_eof(ip, pos, ip->i_size);
+		if (ret) {
+			xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
+			return ret;
+		}
+	}
+	xfs_rw_iunlock(ip, XFS_ILOCK_EXCL);
+
+	/*
+	 * If we're writing the file then make sure to clear the setuid and
+	 * setgid bits if the process is not being run by root.  This keeps
+	 * people from modifying setuid and setgid binaries.
+	 */
+	ret = file_remove_suid(file);
+	if (unlikely(ret))
+		return ret;
+
+	if (mapping->nrpages) {
+		WARN_ON(*iolock != XFS_IOLOCK_EXCL);
+		ret = -xfs_flushinval_pages(ip, (pos & PAGE_CACHE_MASK), -1,
+							FI_REMAPF_LOCKED);
+		if (ret)
+			return ret;
+	}
+
+	if (*iolock == XFS_IOLOCK_EXCL) {
+		/* demote the lock now the cached pages are gone */
+		xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
+		*iolock = XFS_IOLOCK_SHARED;
+	}
+
+	trace_xfs_file_direct_write(ip, count, iocb->ki_pos, 0);
+	ret = generic_file_direct_write(iocb, iovp,
+			&nr_segs, pos, &iocb->ki_pos, count, ocount);
+
+	/* No fallback to buffered IO on errors for XFS. */
+	ASSERT(ret < 0 || ret == count);
+	return ret;
+}
+
 STATIC ssize_t
 xfs_file_aio_write(
 	struct kiocb		*iocb,
@@ -670,12 +780,12 @@ xfs_file_aio_write(
 
 relock:
 	if (ioflags & IO_ISDIRECT) {
-		iolock = XFS_IOLOCK_SHARED;
-	} else {
-		iolock = XFS_IOLOCK_EXCL;
+		ret = xfs_file_dio_aio_write(iocb, iovp, nr_segs, pos,
+						ocount, &iolock);
+		goto done_io;
 	}
+	iolock = XFS_IOLOCK_EXCL;
 
-start:
 	xfs_rw_ilock(ip, XFS_ILOCK_EXCL|iolock);
 	ret = generic_write_checks(file, &pos, &count,
 					S_ISBLK(inode->i_mode));
@@ -684,30 +794,6 @@ xfs_file_aio_write(
 		return ret;
 	}
 
-	if (ioflags & IO_ISDIRECT) {
-		xfs_buftarg_t	*target =
-			XFS_IS_REALTIME_INODE(ip) ?
-				mp->m_rtdev_targp : mp->m_ddev_targp;
-
-		if ((pos & target->bt_smask) || (count & target->bt_smask)) {
-			xfs_rw_iunlock(ip, XFS_ILOCK_EXCL|iolock);
-			return XFS_ERROR(-EINVAL);
-		}
-
-		/*
-		 * For direct I/O, if there are cached pages or we're extending
-		 * the file, we need IOLOCK_EXCL until we're sure the bytes at
-		 * the new EOF have been zeroed and/or the cached pages are
-		 * flushed out.  Upgrade the I/O lock and start again.
-		 */
-		if (iolock != XFS_IOLOCK_EXCL &&
-		    (mapping->nrpages || pos > ip->i_size)) {
-			xfs_rw_iunlock(ip, XFS_ILOCK_EXCL|iolock);
-			iolock = XFS_IOLOCK_EXCL;
-			goto start;
-		}
-	}
-
 	new_size = pos + count;
 	if (new_size > ip->i_size)
 		ip->i_new_size = new_size;
@@ -746,41 +832,7 @@ xfs_file_aio_write(
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
 
-	if ((ioflags & IO_ISDIRECT)) {
-		if (mapping->nrpages) {
-			WARN_ON(iolock != XFS_IOLOCK_EXCL);
-			ret = -xfs_flushinval_pages(ip,
-					(pos & PAGE_CACHE_MASK),
-					-1, FI_REMAPF_LOCKED);
-			if (ret)
-				goto out_unlock_internal;
-		}
-
-		if (iolock == XFS_IOLOCK_EXCL) {
-			/* demote the lock now the cached pages are gone */
-			xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
-			iolock = XFS_IOLOCK_SHARED;
-		}
-
-		trace_xfs_file_direct_write(ip, count, iocb->ki_pos, ioflags);
-		ret = generic_file_direct_write(iocb, iovp,
-				&nr_segs, pos, &iocb->ki_pos, count, ocount);
-
-		/*
-		 * direct-io write to a hole: fall through to buffered I/O
-		 * for completing the rest of the request.
-		 */
-		if (ret >= 0 && ret != count) {
-			XFS_STATS_ADD(xs_write_bytes, ret);
-
-			pos += ret;
-			count -= ret;
-
-			ioflags &= ~IO_ISDIRECT;
-			xfs_rw_iunlock(ip, iolock);
-			goto relock;
-		}
-	} else {
+	if (!(ioflags & IO_ISDIRECT)) {
 		int enospc = 0;
 
 write_retry:
@@ -802,6 +854,7 @@ xfs_file_aio_write(
 
 	current->backing_dev_info = NULL;
 
+done_io:
 	xfs_aio_write_isize_update(inode, &iocb->ki_pos, ret);
 
 	if (ret <= 0)