From 137a762eca0389d91a14f830cb1e29b1d483a112 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Wed, 3 Jun 2015 23:19:13 +0200
Subject: disk/edisk: fix blank mode

there where two problems with blank (-b flag):

we did not update the backup header when there was already a valid
backup header in place. we always want to initialize a new backup header
in blank mode!

we now also check the backup header matches the primary (or the other
way arround depending on which header could be read), reporting any
mismatches and restoring the backup from the data of the primary.

the protective mbr needs to start at sector 1 not 0 (apparently, this
matters for ovmf).
---
 sys/src/cmd/disk/prep/edisk.c | 47 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 6 deletions(-)

diff --git a/sys/src/cmd/disk/prep/edisk.c b/sys/src/cmd/disk/prep/edisk.c
index d8edc846a..cd2800815 100644
--- a/sys/src/cmd/disk/prep/edisk.c
+++ b/sys/src/cmd/disk/prep/edisk.c
@@ -610,6 +610,33 @@ readtab(Edit *edit, Header *hdr)
 	return 0;
 }
 
+static char*
+checkhdr(Header *a, Header *b)
+{
+	if(memcmp(a->sig, b->sig, sizeof(a->sig)) != 0)
+		return "signature";
+	if(memcmp(a->rev, b->rev, sizeof(a->rev)) != 0)
+		return "revision";
+	if(memcmp(a->hdrsiz, b->hdrsiz, sizeof(a->hdrsiz)) != 0)
+		return "header size";
+	if(memcmp(a->selflba, b->backlba, sizeof(a->selflba)) != 0
+	|| memcmp(a->backlba, b->selflba, sizeof(a->backlba)) != 0)
+		return "backup lba/self lba";
+	if(memcmp(a->firstlba, b->firstlba, sizeof(a->firstlba)) != 0)
+		return "first lba";
+	if(memcmp(a->lastlba, b->lastlba, sizeof(a->lastlba)) != 0)
+		return "last lba";
+	if(memcmp(a->devid, b->devid, sizeof(a->devid)) != 0)
+		return "device guid";
+	if(memcmp(a->entrycount, b->entrycount, sizeof(a->entrycount)) != 0)
+		return "entry count";
+	if(memcmp(a->entrysize, b->entrysize, sizeof(a->entrysize)) != 0)
+		return "entry size";
+	if(memcmp(a->tabcrc, b->tabcrc, sizeof(a->tabcrc)) != 0)
+		return "table checksum";
+	return nil;
+}
+
 static Header*
 getbakhdr(Edit *edit, Header *bhdr)
 {
@@ -619,9 +646,17 @@ getbakhdr(Edit *edit, Header *bhdr)
 
 	siz = getle32(bhdr->hdrsiz);
 	lba = getle64(bhdr->backlba);
-	hdr = readhdr(edit->disk, lba);
-	if(hdr != nil)
-		return hdr;
+
+	if(!blank){
+		char *mismatch;
+
+		mismatch = "data";
+		hdr = readhdr(edit->disk, lba);
+		if(hdr != nil && (mismatch = checkhdr(bhdr, hdr)) == nil)
+			return hdr;
+		fprint(2, "backup header at lba %lld has mismatching %s, restoring.\n",
+			lba, mismatch);
+	}
 
 	hdr = getblock(edit->disk, lba);
 	memmove(hdr, bhdr, siz);
@@ -756,13 +791,13 @@ initmbr(Disk *disk)
 	t->type = 0xEE;
 	t->active = 0;
 
-	size = disk->secs > 0xFFFFFFFF ? 0xFFFFFFFF : disk->secs;
-	putle32(t->lba, 0);
+	size = (disk->secs - 1) > 0xFFFFFFFF ? 0xFFFFFFFF : (disk->secs - 1);
+	putle32(t->lba, 1);
 	putle32(t->size, size);
 
 	t->starth = 0;
 	t->startc = 0;
-	t->starts = 0;
+	t->starts = 1;
 	t->endh = disk->h-1;
 	t->ends = (disk->s & 0x3F) | (((disk->c-1)>>2) & 0xC0);
 	t->endc = disk->c-1;
-- 
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