linux-kernel - [PATCH 36/80] staging: lustre: reorder LOV_MAGIC

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Date:	Tue, 16 Aug 2016 16:18:49 -0400
From:	James Simmons <jsimmons@...radead.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org,
	Andreas Dilger <andreas.dilger@...el.com>,
	Oleg Drokin <oleg.drokin@...el.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lustre Development List <lustre-devel@...ts.lustre.org>,
	Fan Yong <fan.yong@...el.com>,
	James Simmons <jsimmons@...radead.org>
Subject: [PATCH 36/80] staging: lustre: reorder LOV_MAGIC_* definition

From: Fan Yong <fan.yong@...el.com>

Since all the LOV_MAGIC_* definitions have the same
postfix values break that value out into its own
definition. With this we can check whether the magic's
postfix match the LOV_MAGIC_MAGIC or not: if yes,
then it is quite possible that the clients has
encountered an newer LOV magic. This extra information
can let us handle those cases more gracefully.

Signed-off-by: Fan Yong <fan.yong@...el.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4941
Reviewed-on: http://review.whamcloud.com/10045
Reviewed-by: Andreas Dilger <andreas.dilger@...el.com>
Reviewed-by: Oleg Drokin <oleg.drokin@...el.com>
Signed-off-by: James Simmons <jsimmons@...radead.org>
---
 .../lustre/lustre/include/lustre/lustre_idl.h      |   20 +++++++++++++++-----
 1 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/staging/lustre/lustre/include/lustre/lustre_idl.h b/drivers/staging/lustre/lustre/include/lustre/lustre_idl.h
index d3a9db9..3444add 100644
--- a/drivers/staging/lustre/lustre/include/lustre/lustre_idl.h
+++ b/drivers/staging/lustre/lustre/include/lustre/lustre_idl.h
@@ -1478,11 +1478,21 @@ enum obdo_flags {
 	OBD_FL_LOCAL_MASK   = 0xF0000000,
 };
 
-#define LOV_MAGIC_V1      0x0BD10BD0
-#define LOV_MAGIC	 LOV_MAGIC_V1
-#define LOV_MAGIC_JOIN_V1 0x0BD20BD0
-#define LOV_MAGIC_V3      0x0BD30BD0
-#define LOV_MAGIC_MIGRATE 0x0BD40BD0
+/*
+ * All LOV EA magics should have the same postfix, if some new version
+ * Lustre instroduces new LOV EA magic, then when down-grade to an old
+ * Lustre, even though the old version system does not recognizes such
+ * new magic, it still can distinguish the corrupted cases by checking
+ * the magic's postfix.
+ */
+#define LOV_MAGIC_MAGIC 0x0BD0
+#define LOV_MAGIC_MASK  0xFFFF
+
+#define LOV_MAGIC_V1		(0x0BD10000 | LOV_MAGIC_MAGIC)
+#define LOV_MAGIC_JOIN_V1	(0x0BD20000 | LOV_MAGIC_MAGIC)
+#define LOV_MAGIC_V3		(0x0BD30000 | LOV_MAGIC_MAGIC)
+#define LOV_MAGIC_MIGRATE	(0x0BD40000 | LOV_MAGIC_MAGIC)
+#define LOV_MAGIC		LOV_MAGIC_V1
 
 /*
  * magic for fully defined striping
-- 
1.7.1