partitions/efi: use lba-aware partition records

The kernel's GPT implementation currently uses the generic 'struct
partition' type for dealing with legacy MBR partition records.  While this
is is useful for disklabels that we designed for CHS addressing, such as
msdos, it doesn't adapt well to newer standards that use LBA instead, such
as GUID partition tables.  Furthermore, these generic partition structures
do not have all the required fields to properly follow the UEFI specs.

While a CHS address can be translated to LBA, it's much simpler and
cleaner to just replace the partition type.  This patch adds a new
'gpt_record' type that is fully compliant with EFI and will allow, in the
next patches, to add more checks to properly verify a protective MBR,
which is paramount to probing a device that makes use of GPT.

[[email protected]: coding-style fixes]
Signed-off-by: Davidlohr Bueso <[email protected]>
Reviewed-by: Karel Zak <[email protected]>
Acked-by: Matt Fleming <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

block/partitions/efi.c

@@ -149,12 +149,11 @@ static u64 last_lba(struct block_device *bdev)
 		       bdev_logical_block_size(bdev)) - 1ULL;
 }
 
-static inline int
-pmbr_part_valid(struct partition *part)
+static inline int pmbr_part_valid(gpt_mbr_record *part)
 {
-        if (part->sys_ind == EFI_PMBR_OSTYPE_EFI_GPT &&
-            le32_to_cpu(part->start_sect) == 1UL)
-                return 1;
+	if (part->os_type == EFI_PMBR_OSTYPE_EFI_GPT &&
+	    le32_to_cpu(part->start_sector) == 1UL)
+		return 1;
         return 0;
 }
 

block/partitions/efi.h

@@ -101,11 +101,25 @@ typedef struct _gpt_entry {
 	efi_char16_t partition_name[72 / sizeof (efi_char16_t)];
 } __attribute__ ((packed)) gpt_entry;
 
+typedef struct _gpt_mbr_record {
+	u8	boot_indicator; /* unused by EFI, set to 0x80 for bootable */
+	u8	start_head;     /* unused by EFI, pt start in CHS */
+	u8	start_sector;   /* unused by EFI, pt start in CHS */
+	u8	start_track;
+	u8	os_type;        /* EFI and legacy non-EFI OS types */
+	u8	end_head;       /* unused by EFI, pt end in CHS */
+	u8	end_sector;     /* unused by EFI, pt end in CHS */
+	u8	end_track;      /* unused by EFI, pt end in CHS */
+	__le32	starting_lba;   /* used by EFI - start addr of the on disk pt */
+	__le32	size_in_lba;    /* used by EFI - size of pt in LBA */
+} __packed gpt_mbr_record;
+
+
 typedef struct _legacy_mbr {
 	u8 boot_code[440];
 	__le32 unique_mbr_signature;
 	__le16 unknown;
-	struct partition partition_record[4];
+	gpt_mbr_record partition_record[4];
 	__le16 signature;
 } __attribute__ ((packed)) legacy_mbr;