libfdisk: (gpt) allow to work with hybrid GPT

Notes:

 * fdisk don't sync hybrid MBR with GPT
 * hybrid MBR is ignored and not overwritten by PBMR
 * users is informed about expert command 'M' to toggle between MBR
   and GPT mode. It's possible to manually modify hybrid MBR.

Signed-off-by: Karel Zak <kzak@redhat.com>

4 files changed, 24 insertions, 7 deletions

diff --git a/fdisks/fdisk.c b/fdisks/fdisk.c
index ca49606a5..874f9d138 100644
--- a/fdisks/fdisk.c
+++ b/fdisks/fdisk.c
@@ -546,7 +546,11 @@ int main(int argc, char **argv)
 		if (!fdisk_dev_has_disklabel(cxt)) {
 			fdisk_info(cxt, _("Device does not contain a recognized partition table."));
 			fdisk_create_disklabel(cxt, NULL);
-		}
+
+		} else if (fdisk_is_disklabel(cxt, GPT) && fdisk_gpt_is_hybrid(cxt))
+			fdisk_warnx(cxt, _(
+				  "The hybrid GPT detected. You have to sync "
+				  "the hybrid MBR manually (expert command 'M')."));
 
 		while (1)
 			process_fdisk_menu(&cxt);
diff --git a/libfdisk/src/dos.c b/libfdisk/src/dos.c
index 11d3c71f4..8b51b8c53 100644
--- a/libfdisk/src/dos.c
+++ b/libfdisk/src/dos.c
@@ -815,7 +815,11 @@ static int add_partition(struct fdisk_context *cxt, size_t n, struct fdisk_partt
 	}
 	fill_bounds(cxt, first, last);
 	if (n < 4) {
-		start = cxt->first_lba;
+		if (cxt->parent && fdisk_is_disklabel(cxt->parent, GPT))
+			start = 1;		/* Bad boy modifies hybrid MBR */
+		else
+			start = cxt->first_lba;
+
 		if (fdisk_context_use_cylinders(cxt) || !cxt->total_sectors)
 			limit = cxt->geom.heads * cxt->geom.sectors * cxt->geom.cylinders - 1;
 		else
diff --git a/libfdisk/src/gpt.c b/libfdisk/src/gpt.c
index 68eddeb80..f4c46b94d 100644
--- a/libfdisk/src/gpt.c
+++ b/libfdisk/src/gpt.c
@@ -1476,16 +1476,14 @@ fail:
 static int gpt_write_disklabel(struct fdisk_context *cxt)
 {
 	struct fdisk_gpt_label *gpt;
+	int mbr_type;
 
 	assert(cxt);
 	assert(cxt->label);
 	assert(fdisk_is_disklabel(cxt, GPT));
 
 	gpt = self_label(cxt);
-
-	/* we do not want to mess up hybrid MBRs by creating a valid pmbr */
-	if (valid_pmbr(cxt) == GPT_MBR_HYBRID)
-		goto err0;
+	mbr_type = valid_pmbr(cxt);
 
 	/* check that disk is big enough to handle the backup header */
 	if (le64_to_cpu(gpt->pheader->alternative_lba) > cxt->total_sectors)
@@ -1522,7 +1520,11 @@ static int gpt_write_disklabel(struct fdisk_context *cxt)
 		goto err1;
 	if (gpt_write_header(cxt, gpt->pheader, GPT_PRIMARY_PARTITION_TABLE_LBA) != 0)
 		goto err1;
-	if (gpt_write_pmbr(cxt) != 0)
+
+	if (mbr_type == GPT_MBR_HYBRID)
+		fdisk_warnx(cxt, _("The device contains hybrid MBR -- writing GPT only. "
+				   "You have to sync the MBR manually."));
+	else if (gpt_write_pmbr(cxt) != 0)
 		goto err1;
 
 	DBG(LABEL, dbgprint("GPT write success"));
@@ -2164,6 +2166,12 @@ int fdisk_gpt_partition_set_name(struct fdisk_context *cxt, size_t i)
 	return 0;
 }
 
+int fdisk_gpt_is_hybrid(struct fdisk_context *cxt)
+{
+	assert(cxt);
+	return valid_pmbr(cxt) == GPT_MBR_HYBRID;
+}
+
 static int gpt_toggle_partition_flag(
 		struct fdisk_context *cxt,
 		size_t i,
diff --git a/libfdisk/src/libfdisk.h b/libfdisk/src/libfdisk.h
index 77892d271..f653b48b1 100644
--- a/libfdisk/src/libfdisk.h
+++ b/libfdisk/src/libfdisk.h
@@ -199,6 +199,7 @@ enum {
 
 extern int fdisk_gpt_partition_set_uuid(struct fdisk_context *cxt, size_t i);
 extern int fdisk_gpt_partition_set_name(struct fdisk_context *cxt, size_t i);
+extern int fdisk_gpt_is_hybrid(struct fdisk_context *cxt);
 
 /* dos.c */
 extern struct dos_partition *fdisk_dos_get_partition(