ceph: fix sync and dio writes across stripe boundaries

We were iterating across stripe boundaries properly, but not moving the
write buffer pointer forward.  This caused us to rewrite the same data
after the break.  Fix by adjusting the data pointer forward, and
recalculating the io and buffer alignment after the break.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/file.c

@@ -476,9 +476,6 @@ static ssize_t ceph_sync_write(struct file *file, const char __user *data,
 	else
 		pos = *offset;
 
-	io_align = pos & ~PAGE_MASK;
-	buf_align = (unsigned long)data & ~PAGE_MASK;
-
 	ret = filemap_write_and_wait_range(inode->i_mapping, pos, pos + left);
 	if (ret < 0)
 		return ret;
@@ -502,6 +499,8 @@ static ssize_t ceph_sync_write(struct file *file, const char __user *data,
 	 * boundary.  this isn't atomic, unfortunately.  :(
 	 */
 more:
+	io_align = pos & ~PAGE_MASK;
+	buf_align = (unsigned long)data & ~PAGE_MASK;
 	len = left;
 	if (file->f_flags & O_DIRECT) {
 		/* write from beginning of first page, regardless of
@@ -591,6 +590,7 @@ static ssize_t ceph_sync_write(struct file *file, const char __user *data,
 		pos += len;
 		written += len;
 		left -= len;
+		data += written;
 		if (left)
 			goto more;