[Bug 1835660] Re: initramfs unpacking failed

[Dimitri John Ledkov]

so what grub is doing is correct.

It pads/aligns every initrd by 4, which is fine, and as per spec.

https://www.kernel.org/doc/html/latest/driver-api/early-userspace
/buffer-format.html

initramfs size can be filled with arbitrary amount of "\0" all the way
upto initramfs_size.

"In human terms, the initramfs buffer contains a collection of
compressed and/or uncompressed cpio archives (in the “newc” or “crc”
formats); arbitrary amounts zero bytes (for padding) can be added
between members."

Thus it feels to me that decompress_unlz4.c method in the kernel does
not correctly stop decompressing and returning consumed output position
(posp).

For example, decompress_inflate.c skips over trailer and updates output
pos by 8, at the end of successful conversion.

Similarly unlzma also updates posp at the end of conversion.

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https://bugs.launchpad.net/bugs/1835660

Title:
  initramfs unpacking failed

Status in OEM Priority Project:
  New
Status in grub2 package in Ubuntu:
  Invalid
Status in initramfs-tools package in Ubuntu:
  Invalid
Status in linux package in Ubuntu:
  Triaged

Bug description:
  "initramfs unpacking failed: Decoding failed",  message appears on
  boot up.

  If I "update-initramfs" using gzip instead of lz, then boot up passes
  without decoding failed message.

  ---

  However, we currently believe that the decoding error reported in
  dmesg is actually harmless and has no impact on usability on the
  system.

  Switching from lz4 to gzip compression, simply papers over the
  warning, without any benefits, and slows down boot.

  Kernel should be fixed to correctly parse lz4 compressed initrds, or
  at least lower the warning, to not be user visible as an error.

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