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buildextend-live: drop legacy embed headers #2455

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Merged
bgilbert merged 1 commit into from
Feb 20, 2022
Merged

buildextend-live: drop legacy embed headers #2455

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102 changes: 11 additions & 91 deletions src/cmd-buildextend-live
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Original file line number Diff line number Diff line change
Expand Up @@ -210,17 +210,6 @@ def make_stream_hash(src, dest):
outf.write(hashlib.sha256(buf).hexdigest() + '\n')


def file_offset_in_iso(isoinfo, filename):
# -rw-rw-r-- 1 1750 1750 553961457 Sep 18 2019 [ 4733 00] filename
# match the logical block number ^^^^ ||
# file type, always 00 ^^
matches = list(re.finditer(r'\[\s*([0-9]+) 00\]\s+{}\s*$'.format(filename),
isoinfo, re.MULTILINE))
if len(matches) != 1:
raise Exception('Found {} copies of {}'.format(len(matches), filename))
return int(matches[0].group(1)) * 2048 # assume 2 KB per logical block


def generate_iso():
# convention for kernel and initramfs names
kernel_img = 'vmlinuz'
Expand Down Expand Up @@ -284,7 +273,13 @@ def generate_iso():
with open(stamppath, 'w') as fh:
fh.write(args.build + '\n')

# Add placeholder for Ignition CPIO file
# Add placeholder for Ignition CPIO file. This allows an external tool,
# `coreos-installer iso ignition embed`, to modify an existing ISO image
# to embed a user's custom Ignition config. The tool wraps the Ignition
# config in a cpio.xz and write it directly into this file in the ISO
# image. The cpio.xz will be read into the initramfs filesystem at
# runtime and the Ignition Dracut module will ensure that the config is
# moved where Ignition will see it.
with open(os.path.join(tmpisoimages, ignition_img), 'wb') as fdst:
fdst.write(bytes(ignition_img_size))

Expand Down Expand Up @@ -353,7 +348,6 @@ def generate_iso():
kargs = ' '.join(kargs_array)
print(f'Substituting ISO kernel arguments: {kargs}')

files_with_karg_embed_areas = {}
kargs_json = {'files': []}
cmdline = ''
karg_embed_area_length = 0
Expand Down Expand Up @@ -386,26 +380,21 @@ def generate_iso():
raise Exception(f'Default cmdline is different: "{cmdline}" != "{file_kargs}"')

length = karg_area_end.start() + len(karg_area_end[1]) - karg_area_start.start()
files_with_karg_embed_areas[dstfile] = karg_area_start.start()
kargs_json['files'].append({
'path': os.path.join(dir_suffix, filename),
'offset': karg_area_start.start(),
})
if karg_embed_area_length == 0:
karg_embed_area_length = length
elif length != karg_embed_area_length:
raise Exception(f"Karg embed areas of varying length {list(files_with_karg_embed_areas)}")
raise Exception(f"Karg embed areas of varying length {kargs_json['files']}")
with open(dstfile, 'w') as fh:
fh.write(buf)
shutil.copystat(srcfile, dstfile)
print(f'{srcfile} -> {dstfile}')

if len(files_with_karg_embed_areas) > 0:
if karg_embed_area_length > 0:
assert(karg_embed_area_length > len(cmdline))
with open(os.path.join(tmpisoroot, '.cmdline'), 'w') as fh:
fh.write('#' * karg_embed_area_length)
fh.seek(0)
fh.write(cmdline)
kargs_json.update(
size=karg_embed_area_length,
default=cmdline.strip(),
Expand Down Expand Up @@ -610,6 +599,8 @@ boot
if os.path.exists(os.path.join(tmpisoroot, f['path']))]
kargs_json['files'].sort(key=lambda f: f['path'])
if kargs_json['files']:
# Store the location of "karg embed areas" for use by
# `coreos-installer iso kargs modify`
with open(os.path.join(tmpisocoreos, kargs_file), 'w') as fh:
json.dump(kargs_json, fh, indent=2, sort_keys=True)
fh.write('\n')
Expand Down Expand Up @@ -661,77 +652,6 @@ boot
run_verbose(genisoargs_minimal)
if basearch == "x86_64":
run_verbose(['/usr/bin/isohybrid', '--uefi', f'{tmpisofile}.minimal'])

isoinfo = run_verbose(['isoinfo', '-lR', '-i', tmpisofile],
stdout=subprocess.PIPE, text=True).stdout

# We've already created a file in the ISO with ignition_img_size
# bytes of zeroes. Find the byte offset of that file within the ISO
# image and write it into a custom header at the end of the ISO 9660
# System Area, which is 32 KB at the start of the image "reserved for
# system use". The System Area usually contains partition tables and
# the like, and we're assuming that none of our platforms use the last
# 24 bytes of it.
#
# This allows an external tool, `coreos-installer iso embed`, to modify
# an existing ISO image to embed a user's custom Ignition config.
# The tool wraps the Ignition config in a cpio.gz and uses our header
# to write it directly into the ISO image. The cpio.gz will be read
# into the initramfs filesystem at runtime and the Ignition Dracut module
# will ensure that the config is moved where Ignition will see it.
#
# Skip on s390x because that platform uses an embedded El Torito image
# with its own copy of the initramfs.
#
# Recently, we also play a similar trick for injecting kernel arguments: we
# store the location of "karg embed areas" at the end of the System Area
# (in the 72 bytes before the 24 bytes for the initrd info). This is then
# picked up by `coreos-installer iso embed-kargs`.
if basearch != "s390x":
# size of System Area section at start of ISO9660 images
ISO_SYSTEM_AREA_SIZE = 32768

# number of karg files we allow for in the format
MAX_KARG_FILES = 6

# prune out karg files which don't exist anymore
files_with_karg_embed_areas = {k: v for (k, v) in
files_with_karg_embed_areas.items() if
os.path.exists(k)}

assert len(files_with_karg_embed_areas) <= MAX_KARG_FILES

# these can really never change without ratcheting on the
# coreos-installer side first
INITRDFMT = '<8s2Q'
assert struct.calcsize(INITRDFMT) == 24
KARGSFMT = f"<8s{MAX_KARG_FILES+1+1}Q" # +1 for area length and +1 for offset to default read-only '.cmdline'
assert struct.calcsize(KARGSFMT) == 72

# Start of the Ignition padding within the ISO
offset = file_offset_in_iso(isoinfo, ignition_img)
with open(tmpisofile, 'r+b') as isofh:
# Verify that the calculated byte range is empty
isofh.seek(offset)
if isofh.read(ignition_img_size) != bytes(ignition_img_size):
raise Exception(f'ISO image {ignition_img_size} bytes at {offset} are not zero')

# Write header at the end of the System Area
isofh.seek(ISO_SYSTEM_AREA_SIZE - (struct.calcsize(INITRDFMT) +
struct.calcsize(KARGSFMT)))

offsets = [0] * (MAX_KARG_FILES + 1) # +1 for offset to default
# This is ours default read-only '.cmdline' file, which is used for `coreos-installer iso kargs reset ISO`
offsets[0] = file_offset_in_iso(isoinfo, '.cmdline')

for i, fn in enumerate(files_with_karg_embed_areas):
offset_in_file = files_with_karg_embed_areas[fn]
offsets[i + 1] = file_offset_in_iso(isoinfo, os.path.basename(fn)) + offset_in_file
isofh.write(struct.pack(KARGSFMT, b'coreKarg', karg_embed_area_length, *offsets))
# Magic number + offset + length
isofh.write(struct.pack(INITRDFMT, b'coreiso+', offset, ignition_img_size))
print(f'Embedded {ignition_img_size} bytes Ignition config space at {offset}')

# this consumes the minimal image
run_verbose(['coreos-installer', 'iso', 'extract', 'pack-minimal-iso',
tmpisofile, f'{tmpisofile}.minimal', "--consume"])
Expand Down