[RFC PATCH 0/6] initramfs: reduce buffer footprint

[David Disseldorp <ddiss@suse.de>]

There are a number of stack, heap and data-segment buffers which are
unnecessary for initramfs unpacking. This patchset attempts to remove
them by:
- parsing cpio hex strings in place, instead of copying them for
  nul-termination. (Patches 1 & 2).
- reusing a single heap buffer for cpio header, file and symlink paths,
  instead of three separate buffers. (Patches 3 & 4).
- reusing the heap-allocated cpio buffer across both builtin and
  bootloader-provided unpack attempts. (Patch 5).
- reusing the heap-allocated cpio buffer for error messages on
  FSM-exit, instead of a data-segment buffer. (Patch 6).

I've flagged this as an RFC as I'd like to improve the commit messages
and also provide more thorough testing, likely via kunit / kselftest
integration.

Feedback appreciated.

David Disseldorp (6):
      vsprintf: add simple_strntoul
      initramfs: avoid memcpy for hex header fields
      initramfs: remove extra symlink path buffer
      initramfs: merge header_buf and name_buf
      initramfs: reuse buf for built-in and bootloader initramfs
      initramfs: avoid static buffer for error message

 include/linux/kstrtox.h |  1 +
 init/initramfs.c        | 50 +++++++++++++++++++++--------------------
 lib/vsprintf.c          |  7 ++++++
 3 files changed, 34 insertions(+), 24 deletions(-)