* [OE-core][PATCH] wic: Add gpt-hybrid partition layout
@ 2023-08-30 14:20 Joshua Watt
0 siblings, 0 replies; only message in thread
From: Joshua Watt @ 2023-08-30 14:20 UTC (permalink / raw)
To: openembedded-core; +Cc: Joshua Watt
Add support for formatting a disk with a hybrid MBR & GPT partition
scheme. In this scheme, the primary partitioning method is GPT, but a
valid MBR header is also written than can point to a subset of the GPT
partitions on the disk (any partitions marked with the `--mbr` flag will
be included in this MBR). The primary purpose of this method is to allow
for SoCs that can only find a bootloader in an MBR partition to use GPT
once the bootloader is running. As an example, older versions of the
Raspberry Pi firmware can only parse MBR partitions to find a kernel (or
other bootloader like u-boot), but once those have booted GPT partitions
can be used.
In addition to the partitions annotated with the `--mbr`, a "protective"
GPT partition of type 0xEE is added, as the existence of such a
partition is the indication to tooling that this a hybrid MBR and that
the GPT partition table should be parsed instead.
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
---
scripts/lib/wic/ksparser.py | 3 +-
scripts/lib/wic/partition.py | 1 +
scripts/lib/wic/plugins/imager/direct.py | 82 +++++++++++++++++++-----
3 files changed, 69 insertions(+), 17 deletions(-)
diff --git a/scripts/lib/wic/ksparser.py b/scripts/lib/wic/ksparser.py
index 667b2ff9c33..7ef3dc83ddc 100644
--- a/scripts/lib/wic/ksparser.py
+++ b/scripts/lib/wic/ksparser.py
@@ -188,11 +188,12 @@ class KickStart():
part.add_argument('--uuid')
part.add_argument('--fsuuid')
part.add_argument('--no-fstab-update', action='store_true')
+ part.add_argument('--mbr', action='store_true')
bootloader = subparsers.add_parser('bootloader')
bootloader.add_argument('--append')
bootloader.add_argument('--configfile')
- bootloader.add_argument('--ptable', choices=('msdos', 'gpt'),
+ bootloader.add_argument('--ptable', choices=('msdos', 'gpt', 'gpt-hybrid'),
default='msdos')
bootloader.add_argument('--timeout', type=int)
bootloader.add_argument('--source')
diff --git a/scripts/lib/wic/partition.py b/scripts/lib/wic/partition.py
index f11c393df51..b1a2306dd12 100644
--- a/scripts/lib/wic/partition.py
+++ b/scripts/lib/wic/partition.py
@@ -60,6 +60,7 @@ class Partition():
self.has_fstab = False
self.update_fstab_in_rootfs = False
self.hidden = args.hidden
+ self.mbr = args.mbr
self.lineno = lineno
self.source_file = ""
diff --git a/scripts/lib/wic/plugins/imager/direct.py b/scripts/lib/wic/plugins/imager/direct.py
index 55347f5480a..9b619e41c11 100644
--- a/scripts/lib/wic/plugins/imager/direct.py
+++ b/scripts/lib/wic/plugins/imager/direct.py
@@ -342,7 +342,7 @@ class PartitionedImage():
# generate parition and filesystem UUIDs
for part in self.partitions:
if not part.uuid and part.use_uuid:
- if self.ptable_format == 'gpt':
+ if self.ptable_format in ('gpt', 'gpt-hybrid'):
part.uuid = str(uuid.uuid4())
else: # msdos partition table
part.uuid = '%08x-%02d' % (self.identifier, part.realnum)
@@ -398,6 +398,10 @@ class PartitionedImage():
raise WicError("setting custom partition type is not " \
"implemented for msdos partitions")
+ if part.mbr and self.ptable_format != 'gpt-hybrid':
+ raise WicError("Partition may only be included in MBR with " \
+ "a gpt-hybrid partition table")
+
# Get the disk where the partition is located
self.numpart += 1
if not part.no_table:
@@ -406,7 +410,7 @@ class PartitionedImage():
if self.numpart == 1:
if self.ptable_format == "msdos":
overhead = MBR_OVERHEAD
- elif self.ptable_format == "gpt":
+ elif self.ptable_format in ("gpt", "gpt-hybrid"):
overhead = GPT_OVERHEAD
# Skip one sector required for the partitioning scheme overhead
@@ -490,7 +494,7 @@ class PartitionedImage():
# Once all the partitions have been layed out, we can calculate the
# minumim disk size
self.min_size = self.offset
- if self.ptable_format == "gpt":
+ if self.ptable_format in ("gpt", "gpt-hybrid"):
self.min_size += GPT_OVERHEAD
self.min_size *= self.sector_size
@@ -511,22 +515,38 @@ class PartitionedImage():
return exec_native_cmd(cmd, self.native_sysroot)
+ def _write_identifier(self, device, identifier):
+ logger.debug("Set disk identifier %x", identifier)
+ with open(device, 'r+b') as img:
+ img.seek(0x1B8)
+ img.write(identifier.to_bytes(4, 'little'))
+
+ def _make_disk(self, device, ptable_format, min_size):
+ logger.debug("Creating sparse file %s", device)
+ with open(device, 'w') as sparse:
+ os.ftruncate(sparse.fileno(), min_size)
+
+ logger.debug("Initializing partition table for %s", device)
+ exec_native_cmd("parted -s %s mklabel %s" % (device, ptable_format),
+ self.native_sysroot)
+
+
def create(self):
- logger.debug("Creating sparse file %s", self.path)
- with open(self.path, 'w') as sparse:
- os.ftruncate(sparse.fileno(), self.min_size)
+ self._make_disk(self.path,
+ "gpt" if self.ptable_format == "gpt-hybrid" else self.ptable_format,
+ self.min_size)
- logger.debug("Initializing partition table for %s", self.path)
- exec_native_cmd("parted -s %s mklabel %s" %
- (self.path, self.ptable_format), self.native_sysroot)
+ self._write_identifier(self.path, self.identifier)
- logger.debug("Set disk identifier %x", self.identifier)
- with open(self.path, 'r+b') as img:
- img.seek(0x1B8)
- img.write(self.identifier.to_bytes(4, 'little'))
+ if self.ptable_format == "gpt-hybrid":
+ mbr_path = self.path + ".mbr"
+ self._make_disk(mbr_path, "msdos", self.min_size)
+ self._write_identifier(mbr_path, self.identifier)
logger.debug("Creating partitions")
+ hybrid_mbr_part_num = 0
+
for part in self.partitions:
if part.num == 0:
continue
@@ -571,7 +591,14 @@ class PartitionedImage():
self._create_partition(self.path, part.type,
parted_fs_type, part.start, part.size_sec)
- if self.ptable_format == "gpt" and (part.part_name or part.label):
+ if self.ptable_format == "gpt-hybrid" and part.mbr:
+ hybrid_mbr_part_num += 1
+ if hybrid_mbr_part_num > 4:
+ raise WicError("Extended MBR partitions are not supported in hybrid MBR")
+ self._create_partition(mbr_path, "primary",
+ parted_fs_type, part.start, part.size_sec)
+
+ if self.ptable_format in ("gpt", "gpt-hybrid") and (part.part_name or part.label):
partition_label = part.part_name if part.part_name else part.label
logger.debug("partition %d: set name to %s",
part.num, partition_label)
@@ -586,7 +613,7 @@ class PartitionedImage():
(part.num, part.part_type,
self.path), self.native_sysroot)
- if part.uuid and self.ptable_format == "gpt":
+ if part.uuid and self.ptable_format in ("gpt", "gpt-hybrid"):
logger.debug("partition %d: set UUID to %s",
part.num, part.uuid)
exec_native_cmd("sgdisk --partition-guid=%d:%s %s" % \
@@ -594,12 +621,16 @@ class PartitionedImage():
self.native_sysroot)
if part.active:
- flag_name = "legacy_boot" if self.ptable_format == 'gpt' else "boot"
+ flag_name = "legacy_boot" if self.ptable_format in ('gpt', 'gpt-hybrid') else "boot"
logger.debug("Set '%s' flag for partition '%s' on disk '%s'",
flag_name, part.num, self.path)
exec_native_cmd("parted -s %s set %d %s on" % \
(self.path, part.num, flag_name),
self.native_sysroot)
+ if self.ptable_format == 'gpt-hybrid' and part.mbr:
+ exec_native_cmd("parted -s %s set %d %s on" % \
+ (mbr_path, hybrid_mbr_part_num, "boot"),
+ self.native_sysroot)
if part.system_id:
exec_native_cmd("sfdisk --part-type %s %s %s" % \
(self.path, part.num, part.system_id),
@@ -612,6 +643,25 @@ class PartitionedImage():
(self.path, part.num),
self.native_sysroot)
+ if self.ptable_format == "gpt-hybrid":
+ # Write a protective GPT partition
+ hybrid_mbr_part_num += 1
+ if hybrid_mbr_part_num > 4:
+ raise WicError("Extended MBR partitions are not supported in hybrid MBR")
+
+ # parted cannot directly create a protective GPT partition, so
+ # create with an arbitrary type, then change it to the correct type
+ # with sfdisk
+ self._create_partition(mbr_path, "primary", "fat32", 1, GPT_OVERHEAD)
+ exec_native_cmd("sfdisk --part-type %s %d 0xee" % (mbr_path, hybrid_mbr_part_num),
+ self.native_sysroot)
+
+ # Copy hybrid MBR
+ with open(mbr_path, "rb") as mbr_file:
+ with open(self.path, "r+b") as image_file:
+ mbr = mbr_file.read(512)
+ image_file.write(mbr)
+
def cleanup(self):
pass
--
2.34.1
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