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assembler/qemu: extra func for writing grub core

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Extract the function that writes the grub2 core to the image file.
The only supported location currently is the MBR gap, which is the
gap between the Master Boot Record and the first partition, which
for historical and performance reasons was aligned to a certain
sector (used to be 64 but now is even larger with 2048). In the
future other locations for the grub2 core will be supported such
as the PReP partition (ppc64le) or bios-boot (GPT hybrid booting).
This commit is contained in:
Christian Kellner 2019-12-22 16:55:34 +01:00 • committed by Tom Gundersen
parent 8fcf7d5c45
commit ccf9994ba6
1 changed files with 20 additions and 12 deletions
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32
assemblers/org.osbuild.qemu
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@ -8,7 +8,7 @@ import shutil
import subprocess
import sys
import tempfile
from typing import List
from typing import List, BinaryIO
import osbuild.remoteloop as remoteloop
STAGE_DESC = "Assemble a bootable partitioned disk image with qemu-img"
@ -338,9 +338,24 @@ def partition_table_from_options(options) -> PartitionTable:
return PartitionTable(pttype, ptuuid, parts)
def grub2_write_core_mbrgap(core_f: BinaryIO,
image_f: BinaryIO,
pt: PartitionTable):
"""Write the core into the MBR gap"""
# For historic and performance reasons the first partition
# is aligned to a specific sector number (used to be 64,
# now it is 2048), which leaves a gap between it and the MBR,
# where the core image can be embedded in; also check it fits
core_size = os.fstat(core_f.fileno()).st_size
partition_offset = pt[0].start_in_bytes
assert core_size < partition_offset - 512
image_f.seek(512)
shutil.copyfileobj(core_f, image_f)
def install_grub2(image: str, pt: PartitionTable, options):
"""Install grub2 to image"""
grub2_core = "/var/tmp/grub2-core.img"
core_path = "/var/tmp/grub2-core.img"
# Create the level-2 & 3 stages of the bootloader, aka the core
# it consists of the kernel plus the core modules required to
@ -394,16 +409,9 @@ def install_grub2(image: str, pt: PartitionTable, options):
# overwritten.
image_f.write(boot_f.read(440))
# Embed Stage-2 in the MBR gap
# For historic and performance reasons the first partition
# is aligned to a specific sector number (used to be 64,
# now it is 2048), which leaves a gap between it and the MBR,
# where the core image can be embedded in; also check it fits
partition_offset = pt[0].start_in_bytes
assert os.path.getsize(grub2_core) < partition_offset - 512
with open(grub2_core, "rb") as core_f:
image_f.seek(512)
shutil.copyfileobj(core_f, image_f)
with open(core_path, "rb") as core_f:
# Embed the core in the gap between the MBR and the fist partition
grub2_write_core_mbrgap(core_f, image_f, pt)
def main(tree, output_dir, options, loop_client):