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image-info: always use raw images and loop devices

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Convert any image that is not a raw image, e.g. a qcow2, to a raw
image and open the partitions via loop devices. This replaces the
usage of nbd, which was racy and flaky.
Instead on relying on the kernel for the partition parsing, this
is now done manually via loop devices and start + offset taken
from sfdisk. As a result the read_partition function has been
adapted to be called at later time, after the partitions were
opened via loop devices.

Not using nbd also means that the partition table is not scanned
by the kernel anymore and udev is not triggered. As a result the
'PARTUUID' property is not present for dos/mbr partition layouts,
since it is auto-generated by udev/blkid. Relevant blkid files
and functions are:
  blkid_partition_gen_uuid(par)
    called from probe_dos_pt()
    in file libblkid/src/partitions/dos.c line 295
    defined in libblkid/src/partitions/partitions.c line 1374
    which generates the uuid via snprintf using the format:
      '"%.33s-%02x", par->tab->id, par->partno'
Based on https://github.com/karelzak/util-linux at ce8985cc7

NB: the loop device code is imported from osbuild, making this
tool depend on osbuild's private library.

NB: As of the image conversion, more disk space is required to
examine non-raw images.
This commit is contained in:
Christian Kellner 2020-07-08 17:21:03 +02:00 • committed by Ondřej Budai
parent bd695c79d2
commit 598c2b6939
1 changed files with 101 additions and 38 deletions
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139
tools/image-info
View file

@ -2,6 +2,7 @@
import argparse
import contextlib
import errno
import functools
import glob
import mimetypes
@ -12,6 +13,8 @@ import sys
import tempfile
import xml.etree.ElementTree
from osbuild import loop
def run_ostree(*args, _input=None, _check=True, **kwargs):
args = list(args) + [f'--{k}={v}' for k, v in kwargs.items()]
@ -25,17 +28,51 @@ def run_ostree(*args, _input=None, _check=True, **kwargs):
@contextlib.contextmanager
def nbd_connect(image):
for device in glob.glob("/dev/nbd*"):
r = subprocess.run(["qemu-nbd", "--connect", device, "--read-only", image], check=False).returncode
if r == 0:
try:
yield device
finally:
subprocess.run(["qemu-nbd", "--disconnect", device], check=True, stdout=subprocess.DEVNULL)
break
else:
raise RuntimeError("no free network block device")
def loop_create_device(ctl, fd, offset=None, sizelimit=None):
while True:
lo = loop.Loop(ctl.get_unbound())
try:
lo.set_fd(fd)
except OSError as e:
lo.close()
if e.errno == errno.EBUSY:
continue
raise e
try:
lo.set_status(offset=offset, sizelimit=sizelimit, autoclear=True)
except BlockingIOError:
lo.clear_fd()
lo.close()
continue
break
try:
yield lo
finally:
lo.close()
@contextlib.contextmanager
def loop_open(ctl, image, *, offset=None, size=None):
with open(image, "rb") as f:
fd = f.fileno()
with loop_create_device(ctl, fd, offset=offset, sizelimit=size) as lo:
yield os.path.join("/dev", lo.devname)
@contextlib.contextmanager
def open_image(ctl, image, fmt):
with tempfile.TemporaryDirectory() as tmp:
if fmt != "raw":
target = os.path.join(tmp, "image.raw")
subprocess.run(["qemu-img", "convert", "-O", "raw", image, target],
check=True)
else:
target = image
size = os.stat(target).st_size
with loop_open(ctl, target, offset=0, size=size) as dev:
yield target, dev
@contextlib.contextmanager
@ -105,18 +142,14 @@ def read_image_format(device):
return qemu["format"]
def read_partition(device, bootable, typ=None, start=0, size=0):
blkid = subprocess_check_output(["blkid", "--output", "export", device], parse_environment_vars)
return {
"label": blkid.get("LABEL"), # doesn't exist for mbr
"type": typ,
"uuid": blkid.get("UUID"),
"partuuid": blkid.get("PARTUUID"),
"fstype": blkid.get("TYPE"),
"bootable": bootable,
"start": start,
"size": size
}
def read_partition(device, partition):
blkid = subprocess_check_output(["blkid", "--output", "export", device],
parse_environment_vars)
partition["label"] = blkid.get("LABEL") # doesn't exist for mbr
partition["uuid"] = blkid.get("UUID")
partition["fstype"] = blkid.get("TYPE")
return partition
def read_partition_table(device):
@ -132,8 +165,28 @@ def read_partition_table(device):
ptable = sfdisk["partitiontable"]
assert ptable["unit"] == "sectors"
for p in ptable["partitions"]:
partitions.append(read_partition(p["node"], p.get("bootable", False), p["type"], p["start"] * 512, p["size"] * 512))
is_dos = ptable["label"] == "dos"
for i, p in enumerate(ptable["partitions"]):
partuuid = p.get("uuid")
if not partuuid and is_dos:
# For dos/mbr partition layouts the partition uuid
# is generated. Normally this would be done by
# udev+blkid, when the partition table is scanned.
# 'sfdisk' prefixes the partition id with '0x' but
# 'blkid' does not; remove it to mimic 'blkid'
table_id = ptable['id'][2:]
partuuid = "%.33s-%02x" % (table_id, i+1)
partitions.append({
"bootable": p.get("bootable", False),
"type": p["type"],
"start": p["start"] * 512,
"size": p["size"] * 512,
"partuuid": partuuid
})
info["partition-table"] = ptable["label"]
info["partition-table-id"] = ptable["id"]
@ -289,33 +342,43 @@ def find_esp(partitions):
return None, 0
def append_partitions(report, device):
esp, esp_id = find_esp(report["partitions"])
def append_partitions(report, device, loctl):
partitions = report["partitions"]
esp, esp_id = find_esp(partitions)
for n, part in enumerate(report["partitions"]):
if not part["fstype"]:
continue
with contextlib.ExitStack() as cm:
with mount(device + f"p{n + 1}") as tree:
if esp and os.path.exists(f"{tree}/boot/efi"):
with mount_at(device + f"p{esp_id + 1}", f"{tree}/boot/efi", options=['umask=077']):
devices = {}
for n, part in enumerate(partitions):
start, size = part["start"], part["size"]
dev = cm.enter_context(loop_open(loctl, device, offset=start, size=size))
devices[n] = dev
read_partition(dev, part)
for n, part in enumerate(partitions):
if not part["fstype"]:
continue
with mount(devices[n]) as tree:
if esp and os.path.exists(f"{tree}/boot/efi"):
with mount_at(devices[esp_id], f"{tree}/boot/efi", options=['umask=077']):
append_filesystem(report, tree)
else:
append_filesystem(report, tree)
else:
append_filesystem(report, tree)
def analyse_image(image):
subprocess.run(["modprobe", "nbd"], check=True)
loctl = loop.LoopControl()
imgfmt = read_image_format(image)
report = {"image-format": imgfmt}
with nbd_connect(image) as device:
with open_image(loctl, image, imgfmt) as (_, device):
report["bootloader"] = read_bootloader_type(device)
report.update(read_partition_table(device))
if report["partition-table"]:
append_partitions(report, device)
append_partitions(report, device, loctl)
else:
with mount(device) as tree:
append_filesystem(report, tree)