From a17bd659e26708a20b64b7a8d733debd761eb7ba Mon Sep 17 00:00:00 2001
From: Dan Bungert <daniel.bungert@canonical.com>
Date: Wed, 9 Mar 2022 16:28:41 -0700
Subject: [PATCH 1/3] filesystem: move MiB constant to fix import loop

---
 subiquity/common/filesystem/manipulator.py | 3 +--
 subiquity/models/filesystem.py             | 3 ++-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/subiquity/common/filesystem/manipulator.py b/subiquity/common/filesystem/manipulator.py
index 3fba58f9..18d9e760 100644
--- a/subiquity/common/filesystem/manipulator.py
+++ b/subiquity/common/filesystem/manipulator.py
@@ -21,13 +21,12 @@ from subiquity.common.filesystem import boot, gaps
 from subiquity.common.types import Bootloader
 from subiquity.models.filesystem import (
     align_up,
+    MiB,
     Partition,
     )
 
 log = logging.getLogger('subiquity.common.filesystem.manipulator')
 
-
-MiB = 1024 * 1024
 BIOS_GRUB_SIZE_BYTES = 1 * MiB
 PREP_GRUB_SIZE_BYTES = 8 * MiB
 
diff --git a/subiquity/models/filesystem.py b/subiquity/models/filesystem.py
index ee0189cb..0ff62c3e 100644
--- a/subiquity/models/filesystem.py
+++ b/subiquity/models/filesystem.py
@@ -33,9 +33,10 @@ from probert.storage import StorageInfo
 
 from subiquity.common.types import Bootloader, OsProber
 
-
 log = logging.getLogger('subiquity.models.filesystem')
 
+MiB = 1024 * 1024
+
 
 def _set_backlinks(obj):
     if obj.id is None:

From d0ccc98aadc489abc4cca24549c654b2a94df74f Mon Sep 17 00:00:00 2001
From: Dan Bungert <daniel.bungert@canonical.com>
Date: Wed, 9 Mar 2022 15:05:40 -0700
Subject: [PATCH 2/3] filesystem: add alignment data

---
 subiquity/models/filesystem.py | 40 ++++++++++++++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

diff --git a/subiquity/models/filesystem.py b/subiquity/models/filesystem.py
index 0ff62c3e..3e343166 100644
--- a/subiquity/models/filesystem.py
+++ b/subiquity/models/filesystem.py
@@ -576,6 +576,10 @@ class Disk(_Device):
 
     _info = attr.ib(default=None)
 
+    def alignment_data(self):
+        ptable = self.ptable_for_new_partition()
+        return self._m._partition_alignment_data[ptable]
+
     def info_for_display(self):
         bus = self._info.raw.get('ID_BUS', None)
         major = self._info.raw.get('MAJOR', None)
@@ -928,12 +932,44 @@ def align_down(size, block_size=1 << 20):
     return size & ~(block_size - 1)
 
 
+@attr.s(auto_attribs=True)
+class PartitionAlignmentData:
+    part_align: int
+    min_gap_size: int
+    min_start_offset: int
+    min_end_offset: int
+    primary_part_limit: int
+    ebr_space: int = 0
+
+
 class FilesystemModel(object):
 
-    lower_size_limit = 128 * (1 << 20)
-
     target = None
 
+    _partition_alignment_data = {
+        'gpt': PartitionAlignmentData(
+            part_align=MiB,
+            min_gap_size=MiB,
+            min_start_offset=GPT_OVERHEAD//2,
+            min_end_offset=GPT_OVERHEAD//2,
+            primary_part_limit=128),
+        'msdos': PartitionAlignmentData(
+            part_align=MiB,
+            min_gap_size=MiB,
+            min_start_offset=GPT_OVERHEAD//2,
+            min_end_offset=0,
+            ebr_space=MiB,
+            primary_part_limit=4),
+        # XXX check this one!!
+        'vtoc': PartitionAlignmentData(
+            part_align=MiB,
+            min_gap_size=MiB,
+            min_start_offset=GPT_OVERHEAD//2,
+            min_end_offset=0,
+            ebr_space=MiB,
+            primary_part_limit=3),
+        }
+
     @classmethod
     def is_mounted_filesystem(self, fstype):
         if fstype in [None, 'swap']:

From 2d325473ac24adb634087675731ba70313618c42 Mon Sep 17 00:00:00 2001
From: Dan Bungert <daniel.bungert@canonical.com>
Date: Wed, 9 Mar 2022 17:05:31 -0700
Subject: [PATCH 3/3] filesystem: test for gap vs align agreement

---
 subiquity/models/tests/test_filesystem.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/subiquity/models/tests/test_filesystem.py b/subiquity/models/tests/test_filesystem.py
index 02c46855..034166bb 100644
--- a/subiquity/models/tests/test_filesystem.py
+++ b/subiquity/models/tests/test_filesystem.py
@@ -661,3 +661,20 @@ class TestAutoInstallConfig(unittest.TestCase):
         self.assertTrue(disk1p1.id in rendered_ids)
         self.assertTrue(disk2.id in rendered_ids)
         self.assertTrue(disk2p1.id in rendered_ids)
+
+
+class TestAlignmentData(unittest.TestCase):
+    def test_alignment_gaps_coherence(self):
+        for ptable in 'gpt', 'msdos', 'vtoc':
+            model = make_model(Bootloader.NONE)
+            disk1 = make_disk(model, ptable=ptable)
+            gaps_max = gaps.largest_gap_size(disk1)
+
+            align_data = disk1.alignment_data()
+            align_max = (disk1.size - align_data.min_start_offset
+                         - align_data.min_end_offset)
+
+            # The alignment data currently has a better notion of end
+            # information, so gaps produces numbers that are too small by 1MiB
+            # for ptable != 'gpt'
+            self.assertTrue(gaps_max <= align_max, f'ptable={ptable}')