Improving grub-mkstandalone for reproducible build

[Michael Chang]

Enclosed is the description from openSUSE bugzilla entry:

While working on reproducible builds for openSUSE, I found that our
grub2 package's /usr/share/grub2/x86_64-xen/grub.xen varies across
builds.

I identified 2 issues: The tar contains changing (octal) mtime values.
The tar stores files in random filesystem readdir order.

The first issue produces such diffs:
--- old /usr/share/grub2/x86_64-xen/grub.xen (objdump)
+++ new /usr/share/grub2/x86_64-xen/grub.xen (objdump)
@@ -4896,7 +4896,7 @@
  01319f 00000000 30303030 36303000 30303031  ....0000600.0001
  0131af 37353000 30303031 37353000 30303030  750.0001750.0000
  0131bf 30303033 34353000 31343533 31323035  0003450.14531205
- 0131cf 35303300 30303135 30313320 30000000  503.0015013 0...
+ 0131cf 36313200 30303135 30313420 30000000  612.0015014 0...
  0131df 00000000 00000000 00000000 00000000  ................
  0131ef 00000000 00000000 00000000 00000000  ................


and the second issue produced this diff:
  01311f 00000000 00000000 01000000 00000000  ................
  01312f 00000000 00000000 01000000 08b42600  ..............&.
  01313f 626f6f74 2f677275 622f7838 365f3634  boot/grub/x86_64
- 01314f 2d78656e 2f646973 6b2e6d6f 64000000  -xen/disk.mod...
+ 01314f 2d78656e 2f6c7378 656e2e6d 6f640000  -xen/lsxen.mod..
  01315f 00000000 00000000 00000000 00000000  ................

The second issue probably comes from grub_util_fd_readdir that would
need to collect+sort entries before further processing.

Furthermore, both patches were developed to address the aforementioned
issues individually. We hope to contribute them to upstream if the
enhancement sounds appealing to others as well.

Thanks.

Michael Chang (2):
  mkstandalone: ensure stable timestamps for generated images
  mkstandalone: ensure deterministic tar file creation by sorting
    contents

 util/grub-mkstandalone.c | 36 ++++++++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 8 deletions(-)

-- 
2.43.0