From 51d5509c8389815c16f16c9b68e17612ed65d136 Mon Sep 17 00:00:00 2001
From: Adrian Vladu <avladu@cloudbasesolutions.com>
Date: Thu, 5 Sep 2024 15:55:36 +0300
Subject: [PATCH] btrfs hack: shrink the allocated size

We are using read-only btrfs compressed for the /usr partition,
and sometimes the free space shown by `btrfs fi usage` and the `df` IS diverging,
with `df` showing the free space from the `btrfs fi usage`'s `Device unallocated.

I have found a way to fix the allocation, by decreasing the size to more than the btrfs
filesystem allows, but curiosly the allocation is getting reset during the failed
attempt and the issue is fixed.

This is of course, a _HACK_, and can at any time produce unwanted behaviours.

Note that the issue cannot be reliably reproduced.

See Flatcar issue: https://github.com/flatcar/Flatcar/issues/1473

See issue upstream:
https://bugzilla.kernel.org/show_bug.cgi?id=219167

Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>
---
 build_library/build_image_util.sh |  2 ++
 build_library/disk_util           | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/build_library/build_image_util.sh b/build_library/build_image_util.sh
index 7712141c36a..5ba0127a233 100755
--- a/build_library/build_image_util.sh
+++ b/build_library/build_image_util.sh
@@ -806,6 +806,8 @@ EOF
     sudo fstrim "${root_fs_dir}/usr" || true
   fi
 
+  "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" btrfsresetallocation \
+      "${root_fs_dir}/usr"
   # Make the filesystem un-mountable as read-write and setup verity.
   if [[ ${disable_read_write} -eq ${FLAGS_TRUE} ]]; then
     # Unmount /usr partition
diff --git a/build_library/disk_util b/build_library/disk_util
index f94317e3c1d..944d27eddba 100755
--- a/build_library/disk_util
+++ b/build_library/disk_util
@@ -768,6 +768,25 @@ def Tune(options):
   if not action_done:
     raise Exception("No options specified!")
 
+def SudoOutputToConsole(cmd):
+  print(SudoOutput(cmd).decode())
+
+def LogBtrfsUsage(mount_point, section=None):
+  print('Btrfs usage for mount point `%s` %s' % (mount_point, section))
+  try:
+      SudoOutputToConsole(['btrfs', 'fi', 'usage', mount_point])
+  except Exception as ex:
+      print('Btrfs usage could not be retrieved for mount point `%s` %s' % (mount_point, section))
+      print(ex)
+
+def BtrfsResetAllocation(options):
+
+    LogBtrfsUsage(options.disk_image, 'before disk resize')
+    try:
+        Sudo(['btrfs', 'fi', 'resize', '-500m', options.disk_image])
+    except Exception as ex:
+        print(ex)
+    LogBtrfsUsage(options.disk_image, 'after disk resize')
 
 def Verity(options):
   """Hash verity protected filesystems.
@@ -1119,6 +1138,10 @@ def main(argv):
   a = actions.add_parser('parseonly', help='validate config')
   a.set_defaults(func=DoParseOnly)
 
+  a = actions.add_parser('btrfsresetallocation', help='btrfs reset allocation')
+  a.add_argument('disk_image', help='path to disk image file')
+  a.set_defaults(func=BtrfsResetAllocation)
+
   options = parser.parse_args(argv[1:])
   options.func(options)