[PATCH v4 0/4] initramfs: "crc" cpio format and INITRAMFS_PRESERVE_MTIME

This patchset does some minor refactoring of cpio header magic checking
and corrects documentation.
Patch 4/4 allows cpio entry mtime preservation to be disabled via a new
INITRAMFS_PRESERVE_MTIME Kconfig option.

Changes since v3, following feedback from Martin Wilck:
- 4/4: keep vfs_utimes() call in do_copy() path
  + drop [PATCH v3 4/5] initramfs: use do_utime() wrapper consistently
  + add do_utime_path() helper
  + clean up timespec64 initialisation
- 4/4: move all mtime preservation logic to initramfs_mtime.h and drop
  separate .c
- 4/4: improve commit message

 .../early-userspace/buffer-format.rst         | 24 +++-----
 init/Kconfig                                  | 10 ++++
 init/initramfs.c                              | 57 +++----------------
 init/initramfs_mtime.h                        | 50 ++++++++++++++++
 4 files changed, 75 insertions(+), 66 deletions(-)