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

From: Nicolas Schier <[email-masked]>
Date: Mon, 18 Aug 2025 20:40:23 +0200

On Thu, Aug 14, 2025 at 03:17:58PM +1000, David Disseldorp wrote:
> 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(-)
> 
> 

Thanks for the series!  I have found only a minor nick pick and some few
bike-shedding things.

Reviewed-by: Nicolas Schier <[email-masked]>

Kind regards,
Nicolas