Increase partition sizes

The /usr partition was too small some time ago and we gained space again
by switching to btrfs with compression and also removing/splitting out
content. The /boot partition is too small all the time and we added
many hacks to fit the kernel+initrd under 60 MB. To handle the case
where the /oem partition is too small for the A/B-updated OEM extensions
we added the workaround to write the inactive one (or both) to the
rootfs. All this would not be needed if we had increased the partition
sizes a few years ago so that we could now assume that most nodes have
the increased sizes and we can make use of them. Still, we can do it now
to prepare for the next time when in five or ten years we have serious
size problems and run out of workarounds. We have to do the change now
and wait a few years so that most nodes have been provisioned with the
new layout. Then we can drop the workarounds and have a full featured
kernel and initrd, and we can also increase the /usr filesystem to make
use of the larger partition. Ideally we use large enough sizes that we
never have to worry again but since we also want to support small ARM
boards which might only have 8 GB internal storage, let's target this
when increasing the partition sizes. With 1 GB /boot, two 2 GB /usr, and
1 GB /oem partitions we are already at 6 GB, leaving 2 GB for the
rootfs. For now, reduce the extracted /usr update payload size to the
current combined filesystem and verity data usage (same size as before).
The rootfs size was also reduced for the initial .bin image so that we
don't overshoot 8 GB - it will be resized to fit the disk anyway on
first boot.

Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>
Signed-off-by: Kai Lueke <kailuke@microsoft.com>

build_library/disk_layout.json

@@ -13,7 +13,7 @@
         "label":"EFI-SYSTEM",
         "fs_label":"EFI-SYSTEM",
         "type":"efi",
-        "blocks":"262144",
+        "blocks":"2097152",
         "fs_type":"vfat",
         "mount":"/boot",
         "features": []
@@ -27,7 +27,8 @@
         "label":"USR-A",
         "uuid":"7130c94a-213a-4e5a-8e26-6cce9662f132",
         "type":"flatcar-rootfs",
-        "blocks":"2097152",
+        "blocks":"4194304",
+        "extract_blocks":"2097152",
         "fs_blocks":"260094",
         "fs_type":"btrfs",
         "fs_compression":"zstd",
@@ -38,7 +39,8 @@
         "label":"USR-B",
         "uuid":"e03dd35c-7c2d-4a47-b3fe-27f15780a57c",
         "type":"flatcar-rootfs",
-        "blocks":"2097152",
+        "blocks":"4194304",
+        "extract_blocks":"2097152",
         "fs_blocks":"262144"
       },
       "5":{
@@ -51,7 +53,7 @@
         "label":"OEM",
         "fs_label":"OEM",
         "type":"data",
-        "blocks":"262144",
+        "blocks":"2097152",
         "fs_type":"btrfs",
         "fs_compression":"zlib",
         "mount":"/oem"
@@ -70,7 +72,7 @@
         "label":"ROOT",
         "fs_label":"ROOT",
         "type":"flatcar-resize",
-        "blocks":"4427776",
+        "blocks":"3653632",
         "fs_type":"ext4",
         "mount":"/"
       }

build_library/disk_util

@@ -40,10 +40,10 @@ def LoadPartitionConfig(options):
       '_comment', 'type', 'num', 'label', 'blocks', 'block_size', 'fs_blocks',
       'fs_block_size', 'fs_type', 'features', 'uuid', 'part_alignment', 'mount',
       'binds', 'fs_subvolume', 'fs_bytes_per_inode', 'fs_inode_size', 'fs_label',
-      'fs_compression'))
+      'fs_compression', 'extract_blocks'))
   integer_layout_keys = set((
       'blocks', 'block_size', 'fs_blocks', 'fs_block_size', 'part_alignment',
-      'fs_bytes_per_inode', 'fs_inode_size'))
+      'fs_bytes_per_inode', 'fs_inode_size', 'extract_blocks'))
   required_layout_keys = set(('type', 'num', 'label', 'blocks'))
 
   filename = options.disk_layout_file
@@ -136,6 +136,13 @@ def LoadPartitionConfig(options):
       part.setdefault('fs_block_size', metadata['fs_block_size'])
       part.setdefault('fs_blocks', part['bytes'] // part['fs_block_size'])
       part['fs_bytes'] = part['fs_blocks'] * part['fs_block_size']
+      # The partition may specify extract_blocks to limit what content gets
+      # extracted. The use case is the /usr partition where we can grow the
+      # partition but can't directly grow the filesystem and the update
+      # payload until all (or most) nodes are running the partition layout
+      # with the grown /usr partition (which can take a few years).
+      if part.get('extract_blocks', None):
+        part['extract_bytes'] = part['extract_blocks'] * metadata['block_size']
 
       if part['fs_bytes'] > part['bytes']:
         raise InvalidLayout(
@@ -823,6 +830,7 @@ def Extract(options):
   if not part['image_compat']:
     raise InvalidLayout("Disk layout is incompatible with existing image")
 
+  extract_size = part.get('extract_bytes', part['image_bytes'])
   subprocess.check_call(['dd',
                          'bs=10MB',
                          'iflag=count_bytes,skip_bytes',
@@ -831,7 +839,7 @@ def Extract(options):
                          'if=%s' % options.disk_image,
                          'of=%s' % options.output,
                          'skip=%s' % part['image_first_byte'],
-                         'count=%s' % part['image_bytes']])
+                         'count=%s' % extract_size])
 
 
 def GetPartitionByNumber(partitions, num):

changelog/changes/2025-10-09-partition-sizes.md

@@ -0,0 +1 @@
+- Increased all partition sizes: `/boot` to 1 GB, the two `/usr` partitions to 2 GB, `/oem` to 1 GB so that we can use more space in a few years when we can assume that most nodes run the new partition layout - existing nodes can still update for the next years ([scripts#3027](https://github.com/flatcar/scripts/pull/3027))