openstack/oslo.utils
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Merge "Avoid detecting FAT VBR as an MBR"

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Zuul 2024-09-24 18:07:00 +00:00 committed by Gerrit Code Review
commit 7381571db7
1 changed files with 18 additions and 1 deletions
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19
oslo_utils/imageutils/format_inspector.py
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@ -1214,6 +1214,7 @@ class GPTInspector(FileInspector):
NAME = 'gpt'
MBR_SIGNATURE = 0xAA55
MBR_PTE_START = 446
MEDIA_TYPE_FDISK = 0xF8
def _initialize(self):
self.new_region('mbr', CaptureRegion(0, 512))
@ -1224,12 +1225,28 @@ class GPTInspector(FileInspector):
# self.new_region('gpt_backup', EndCaptureRegion(512))
self.add_safety_check(SafetyCheck('mbr', self.check_mbr_partitions))
def _check_for_fat(self):
# A FAT filesystem looks like an MBR, but actually starts with a VBR,
# which has the same signature as an MBR, but with more specifics in
# the BPB (BIOS Parameter Block).
boot_sector = self.region('mbr').data
# num_fats is almost always 2 (never more or less) for any filesystem
# not super tiny (think 1980s ramdisk)
num_fats = boot_sector[0x10]
# Media descriptor will basically always be "a fixed disk" for any of
# our purposes, not a floppy disk
media_desc = boot_sector[0x15]
return (num_fats == 2 and media_desc == self.MEDIA_TYPE_FDISK)
@property
def format_match(self):
if not self.region('mbr').complete:
return False
# Check to see if this looks like a VBR from a FAT filesystem so we
# can exclude it
is_fat = self._check_for_fat()
mbr_sig, = struct.unpack('<H', self.region('mbr').data[510:512])
return mbr_sig == self.MBR_SIGNATURE
return mbr_sig == self.MBR_SIGNATURE and not is_fat
def check_mbr_partitions(self):
valid_partitions = []