Subject: [PATCH v2 0/7] gen_init_cpio: add copy_file_range / reflink support

From: David Disseldorp <[email-masked]>
Date: Thu, 14 Aug 2025 15:17:58 +1000

This patchset adds copy_file_range() support to gen_init_cpio. When
combined with data segment alignment, large-file archiving performance
is improved on Btrfs and XFS due to reflinks (see 7/7 benchmarks).

cpio data segment alignment is provided by "bending" the newc spec
to zero-pad the filename field. GNU cpio and Linux initramfs extractors
handle this fine as long as PATH_MAX isn't exceeded.

Changes since v1 RFC
- add alignment patches 6-7
- slightly rework commit and error messages
- rename l->len to avoid 1/i confusion

David Disseldorp (7):
      gen_init_cpio: write to fd instead of stdout stream
      gen_init_cpio: support -o <output_path> parameter
      gen_init_cpio: attempt copy_file_range for file data
      gen_init_cpio: avoid duplicate strlen calls
      gen_initramfs.sh: use gen_init_cpio -o parameter
      docs: initramfs: file data alignment via name padding
      gen_init_cpio: add -a <data_align> as reflink optimization

 .../driver-api/early-userspace/buffer-format.rst   |   5 +
 usr/gen_init_cpio.c                                | 234 ++++++++++++++-------
 usr/gen_initramfs.sh                               |   7 +-
 3 files changed, 166 insertions(+), 80 deletions(-)