From: Michael Neumann <mneumann@ntecs.de>
Date: Sun, 21 Feb 2010 11:39:26 +0000 (+0100)
Subject: HAMMER - Fix mirroring between 32 and 64-bit machines
X-Git-Tag: v2.7.0~156^2~1
X-Git-Url: https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/c7380858c7d940d981d93b5e17984bc652a3cb5c

HAMMER - Fix mirroring between 32 and 64-bit machines

We need to pack struct hammer_pseudofs_data as it had differing sizes
on 32-bit vs. 64-bit machines. As this structure is send over-the-wire
this lead to an early abort in the hammer mirroring code (cmd_mirror.c)
when mirroring a PFS from a 32-bit machine to a 64-bit machine or vice
versa as it sanity checks the packets it gets.

Even so the structure is stored on-media, the change in size is no
issue as the tail is zero-padded with reserved fields.

WARNING:

    After this change, mirroring between 64-bit machines predating
    this commit and updated 64-bit machines will no longer work.
    PLEASE UPDATE them all in one go or leave them unmodified.
    32-bit machines are not affected at all, as this commit does
    not change the size of the structure for 32-bit machines.

Discussed-with: Matthew Dillon
---

diff --git a/sys/vfs/hammer/hammer_disk.h b/sys/vfs/hammer/hammer_disk.h
index 7de627aec6..6871246254 100644
--- a/sys/vfs/hammer/hammer_disk.h
+++ b/sys/vfs/hammer/hammer_disk.h
@@ -798,6 +798,14 @@ struct hammer_symlink_data {
  *
  * sync_low_tid is not yet used but will represent the highest pruning
  * end-point, after which full history is available.
+ *
+ * We need to pack this structure making it equally sized on both 32-bit and
+ * 64-bit machines as it is part of struct hammer_ioc_mrecord_pfs which is
+ * send over the wire in hammer mirror operations. Only on 64-bit machines
+ * the size of this struct differ when packed or not. This leads us to the
+ * situation where old 64-bit systems (using the non-packed structure),
+ * which were never able to mirror to/from 32-bit systems, are now no longer
+ * able to mirror to/from newer 64-bit systems (using the packed structure).
  */
 struct hammer_pseudofs_data {
 	hammer_tid_t	sync_low_tid;	/* full history beyond this point */
@@ -819,7 +827,7 @@ struct hammer_pseudofs_data {
 	int32_t		prune_min;	/* do not prune recent history */
 	int32_t		prune_max;	/* do not retain history beyond here */
 	int32_t		reserved[16];
-};
+} __packed;
 
 typedef struct hammer_pseudofs_data *hammer_pseudofs_data_t;