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[Libguestfs] [PATCH] part-disk: Align whole disk partition to 64 sectors.



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Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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>From 4f6bd18d2e2a9c1d317a07b59072579d8fff42ac Mon Sep 17 00:00:00 2001
From: Richard W.M. Jones <rjones redhat com>
Date: Wed, 6 Oct 2010 09:08:39 +0100
Subject: [PATCH] part-disk: Align whole disk partition to 64 sectors.

Change the part-disk command so it aligns the partition to
64 sectors (instead of 1 or 34 sectors as now).  This should
ensure that the filesystem contained within is aligned.
---
 daemon/parted.c |   24 +++++++++---------------
 1 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/daemon/parted.c b/daemon/parted.c
index 2f928b0..89cc0d6 100644
--- a/daemon/parted.c
+++ b/daemon/parted.c
@@ -178,27 +178,21 @@ do_part_del (const char *device, int partnum)
 int
 do_part_disk (const char *device, const char *parttype)
 {
-  const char *startstr;
-  const char *endstr;
-
   parttype = check_parttype (parttype);
   if (!parttype) {
     reply_with_error ("unknown partition type: common choices are \"gpt\" and \"msdos\"");
     return -1;
   }
 
-  /* Voooooodooooooooo (thanks Jim Meyering for working this out). */
-  if (STREQ (parttype, "msdos")) {
-    startstr = "1s";
-    endstr = "-1s";
-  } else if (STREQ (parttype, "gpt")) {
-    startstr = "34s";
-    endstr = "-34s";
-  } else {
-    /* untested */
-    startstr = "1s";
-    endstr = "-1s";
-  }
+  /* Align all partitions created this way to 64 sectors, and leave
+   * the last 64 sectors at the end of the disk free.  This wastes
+   * 32K+32K = 64K on 512-byte sector disks.  The rationale is:
+   *
+   * - aligned operations are faster
+   * - GPT requires at least 34 sectors at the end of the disk.
+   */
+  const char *startstr = "64s";
+  const char *endstr = "-64s";
 
   RUN_PARTED (return -1,
               device,
-- 
1.7.3.1


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