[PATCH 1/5] partitions: efi: calculate instead of hardcode gpt header fields

[Sascha Hauer]

Calculate the lba values of the GPT header instead of hardcoding them.
This will allow us to modify some fields while preserving a consistent
partition table in the next step.

Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
 common/partitions/efi.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/common/partitions/efi.c b/common/partitions/efi.c
index 840d6a83b7950501debc943864e20e797628720d..92868e4a77e5688d547ee3f2cac3ab9534a4ebdb 100644
--- a/common/partitions/efi.c
+++ b/common/partitions/efi.c
@@ -583,10 +583,13 @@ static __maybe_unused struct partition_desc *efi_partition_create_table(struct b
 {
 	struct efi_partition_desc *epd = xzalloc(sizeof(*epd));
 	gpt_header *gpt;
+	unsigned int num_partition_entries = 128;
+	unsigned int gpt_size = (sizeof(gpt_entry) * num_partition_entries) / SECTOR_SIZE;
+	unsigned int first_usable_lba = gpt_size + 2;
 
 	partition_desc_init(&epd->pd, blk);
 
-	epd->gpt = xzalloc(512);
+	epd->gpt = xzalloc(SECTOR_SIZE);
 	gpt = epd->gpt;
 
 	gpt->signature = cpu_to_le64(GPT_HEADER_SIGNATURE);
@@ -594,18 +597,18 @@ static __maybe_unused struct partition_desc *efi_partition_create_table(struct b
 	gpt->header_size = cpu_to_le32(sizeof(*gpt));
 	gpt->my_lba = cpu_to_le64(1);
 	gpt->alternate_lba = cpu_to_le64(last_lba(blk));
-	gpt->first_usable_lba = cpu_to_le64(34);
-	gpt->last_usable_lba = cpu_to_le64(last_lba(blk) - 34);;
+	gpt->first_usable_lba = cpu_to_le64(first_usable_lba);
+	gpt->last_usable_lba = cpu_to_le64(last_lba(blk) - (gpt_size + 2));;
 	generate_random_guid((unsigned char *)&gpt->disk_guid);
-	gpt->partition_entry_lba = cpu_to_le64(2);
-	gpt->num_partition_entries = cpu_to_le32(128);
+	gpt->partition_entry_lba = cpu_to_le64(first_usable_lba - gpt_size);
+	gpt->num_partition_entries = cpu_to_le32(num_partition_entries);
 	gpt->sizeof_partition_entry = cpu_to_le32(sizeof(gpt_entry));
 
 	add_gpt_diskuuid_param(epd, blk);
 
 	pr_info("Created new disk label with GUID %pU\n", &gpt->disk_guid);
 
-	epd->ptes = xzalloc(128 * sizeof(gpt_entry));
+	epd->ptes = xzalloc(num_partition_entries * sizeof(gpt_entry));
 
 	return &epd->pd;
 }

-- 
2.39.5