[PATCH 4/7] xfs: split direct IO write path from xfs_file_aio_write

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

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.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/xfs/linux-2.6/xfs_file.c |  184 +++++++++++++++++++++++++++---------------
 1 files changed, 118 insertions(+), 66 deletions(-)

diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index 4608aab..d70a249 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -587,6 +587,116 @@ out_lock:
 	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. This also clearly indicates that XFS
+ * does not fall back to buffered IO in the direct IO write path.
+ *
+ * Returns with locks held indicated by @need_i_mutex and @iolock.
+ */
+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			*need_i_mutex,
+	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			error = 0;
+	xfs_fsize_t		new_size;
+	size_t			count = ocount;
+	xfs_buftarg_t		*target = XFS_IS_REALTIME_INODE(ip) ?
+					mp->m_rtdev_targp : mp->m_ddev_targp;
+
+	*need_i_mutex = 0;
+	*iolock = 0;
+	if ((pos & target->bt_smask) || (count & target->bt_smask))
+		return XFS_ERROR(-EINVAL);
+
+	if (mapping->nrpages || pos > ip->i_size) {
+		*iolock = XFS_IOLOCK_EXCL;
+		*need_i_mutex = 1;
+		mutex_lock(&inode->i_mutex);
+	} else {
+		*iolock = XFS_IOLOCK_SHARED;
+	}
+	xfs_ilock(ip, XFS_ILOCK_EXCL|*iolock);
+
+	error = generic_write_checks(file, &pos, &count,
+					S_ISBLK(inode->i_mode));
+	if (error) {
+		xfs_iunlock(ip, XFS_ILOCK_EXCL|*iolock);
+		*iolock = 0;
+		return error;
+	}
+
+	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) {
+		error = -xfs_zero_eof(ip, pos, ip->i_size);
+		if (error) {
+			xfs_iunlock(ip, XFS_ILOCK_EXCL);
+			return error;
+		}
+	}
+	xfs_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.
+	 */
+	error = file_remove_suid(file);
+	if (unlikely(error))
+		return error;
+
+	if (mapping->nrpages) {
+		WARN_ON(*need_i_mutex == 0);
+		error = -xfs_flushinval_pages(ip, (pos & PAGE_CACHE_MASK), -1,
+							FI_REMAPF_LOCKED);
+		if (error)
+			return error;
+	}
+
+	if (*need_i_mutex) {
+		/* demote the lock now the cached pages are gone */
+		xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);
+		mutex_unlock(&inode->i_mutex);
+		*iolock = XFS_IOLOCK_SHARED;
+		*need_i_mutex = 0;
+	}
+
+	trace_xfs_file_direct_write(ip, count, iocb->ki_pos, 0);
+	error = generic_file_direct_write(iocb, iovp,
+			&nr_segs, pos, &iocb->ki_pos, count, ocount);
+
+	/* No fallback to buffered IO on errors for XFS. */
+	return error;
+}
+
 STATIC ssize_t
 xfs_file_aio_write(
 	struct kiocb		*iocb,
@@ -628,19 +738,17 @@ xfs_file_aio_write(
 	if (XFS_FORCED_SHUTDOWN(mp))
 		return -EIO;
 
-relock:
 	if (ioflags & IO_ISDIRECT) {
-		iolock = XFS_IOLOCK_SHARED;
-		need_i_mutex = 0;
-	} else {
-		iolock = XFS_IOLOCK_EXCL;
-		need_i_mutex = 1;
-		mutex_lock(&inode->i_mutex);
+		ret = xfs_file_dio_aio_write(iocb, iovp, nr_segs, pos,
+					ocount, &need_i_mutex, &iolock);
+		goto done_io;
 	}
 
+	iolock = XFS_IOLOCK_EXCL;
+	need_i_mutex = 1;
+	mutex_lock(&inode->i_mutex);
 	xfs_ilock(ip, XFS_ILOCK_EXCL|iolock);
 
-start:
 	error = -generic_write_checks(file, &pos, &count,
 					S_ISBLK(inode->i_mode));
 	if (error) {
@@ -648,26 +756,6 @@ start:
 		goto out_unlock_mutex;
 	}
 
-	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_iunlock(ip, XFS_ILOCK_EXCL|iolock);
-			return XFS_ERROR(-EINVAL);
-		}
-
-		if (!need_i_mutex && (mapping->nrpages || pos > ip->i_size)) {
-			xfs_iunlock(ip, XFS_ILOCK_EXCL|iolock);
-			iolock = XFS_IOLOCK_EXCL;
-			need_i_mutex = 1;
-			mutex_lock(&inode->i_mutex);
-			xfs_ilock(ip, XFS_ILOCK_EXCL|iolock);
-			goto start;
-		}
-	}
-
 	new_size = pos + count;
 	if (new_size > ip->i_size)
 		ip->i_new_size = new_size;
@@ -706,44 +794,7 @@ start:
 	/* 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(need_i_mutex == 0);
-			error = xfs_flushinval_pages(ip,
-					(pos & PAGE_CACHE_MASK),
-					-1, FI_REMAPF_LOCKED);
-			if (error)
-				goto out_unlock_internal;
-		}
-
-		if (need_i_mutex) {
-			/* demote the lock now the cached pages are gone */
-			xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);
-			mutex_unlock(&inode->i_mutex);
-
-			iolock = XFS_IOLOCK_SHARED;
-			need_i_mutex = 0;
-		}
-
-		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_iunlock(ip, iolock);
-			goto relock;
-		}
-	} else {
+	if (!(ioflags & IO_ISDIRECT)) {
 		int enospc = 0;
 		ssize_t ret2 = 0;
 
@@ -767,6 +818,7 @@ write_retry:
 
 	current->backing_dev_info = NULL;
 
+done_io:
 	xfs_aio_write_isize_update(inode, &iocb->ki_pos, ret);
 
 	error = -ret;
-- 
1.7.2.3

_______________________________________________
xfs mailing list
xfs@oss.sgi.com
http://oss.sgi.com/mailman/listinfo/xfs