ceph: explicitly specify page alignment in network messages
The alignment used for reading data into or out of pages used to be taken
from the data_off field in the message header. This only worked as long
as the page alignment matched the object offset, breaking direct io to
non-page aligned offsets.
Instead, explicitly specify the page alignment next to the page vector
in the ceph_msg struct, and use that instead of the message header (which
probably shouldn't be trusted). The alloc_msg callback is responsible for
filling in this field properly when it sets up the page vector.
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/include/linux/ceph/messenger.h b/include/linux/ceph/messenger.h
index 5956d62..a108b42 100644
--- a/include/linux/ceph/messenger.h
+++ b/include/linux/ceph/messenger.h
@@ -82,6 +82,7 @@
struct ceph_buffer *middle;
struct page **pages; /* data payload. NOT OWNER. */
unsigned nr_pages; /* size of page array */
+ unsigned page_alignment; /* io offset in first page */
struct ceph_pagelist *pagelist; /* instead of pages */
struct list_head list_head;
struct kref kref;