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From: "Andrey V. Elsukov" <ae@FreeBSD.org>
Date: Thu, 12 Apr 2012 12:37:53 +0000 (UTC)
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Subject: svn commit: r234176 - head/sys/boot/common
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Author: ae
Date: Thu Apr 12 12:37:53 2012
New Revision: 234176
URL: http://svn.freebsd.org/changeset/base/234176

Log:
  Read backup GPT header from the last LBA only when primary GPT header and
  table aren't valid. If they are ok, use hdr_lba_alt value to read backup
  header. This will make gptboot happy when GPT used atop of some GEOM
  provider, e.g. GEOM_MIRROR.
  
  Reviewed by:	pjd
  MFC after:	2 weeks

Modified:
  head/sys/boot/common/gpt.c

Modified: head/sys/boot/common/gpt.c
==============================================================================
--- head/sys/boot/common/gpt.c	Thu Apr 12 12:15:15 2012	(r234175)
+++ head/sys/boot/common/gpt.c	Thu Apr 12 12:37:53 2012	(r234176)
@@ -337,16 +337,16 @@ gptread(const uuid_t *uuid, struct dsk *
 		gpttable = table_primary;
 	}
 
-	altlba = drvsize(dskp);
-	if (altlba > 0)
-		altlba--;
-	else if (hdr_primary_lba > 0) {
+	if (hdr_primary_lba > 0) {
 		/*
-		 * If we cannot obtain disk size, but primary header
-		 * is valid, we can get backup header location from
-		 * there.
+		 * If primary header is valid, we can get backup
+		 * header location from there.
 		 */
 		altlba = hdr_primary.hdr_lba_alt;
+	} else {
+		altlba = drvsize(dskp);
+		if (altlba > 0)
+			altlba--;
 	}
 	if (altlba == 0)
 		printf("%s: unable to locate backup GPT header\n", BOOTPROG);