Re: [PATCH 4/4] Remove unnecessary cpio_init function

[Stefano Brivio <sbrivio@redhat.com>]

On Fri, 22 Mar 2024 13:27:39 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> The cpio_init function is now only every called with the "discard" option.
> But, moreover, what it does is create an initial mostly empty archive which
> will just get overwritten by the final archive.
> 
> So, it's entirely unnecessary except for one subtlety.  Our use of realpath
> when generating the final output requires that a file already exist in the
> output location.  We can fix that by shuffling some things out of a
> subshell, removing the need for realpath.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  mbuto | 31 ++++---------------------------
>  1 file changed, 4 insertions(+), 27 deletions(-)
> 
> diff --git a/mbuto b/mbuto
> index 550f76e..0c51e18 100755
> --- a/mbuto
> +++ b/mbuto
> @@ -544,28 +544,6 @@ subopts_get() {
>  
>  ### CPIO #######################################################################
>  
> -# cpio_init() - Source existing CPIO archive, or create if needed
> -# $1:	Path to CPIO archive, might exist, might be discarded if existing
> -cpio_init() {
> -	if [ -f "${OUT}" ] && [ "${1}" != "discard" ]; then
> -		info "Sourcing CPIO archive from ${OUT}"
> -
> -		if ! "${GZIP}" -dfc "${OUT}" |
> -		   "${CPIO}" --quiet -iD "${wd}"; then
> -			err "Invalid CPIO archive ${OUT}"
> -		fi
> -	else

This, and the second part of 1/4, remove a functionality which I
accidentally broke in commit b87e4f2e6595 ("mbuto: Create working
directory before profiles are sourced"): it was once possible to add
contents to an existing initramfs archive.

I guess I might be the only interactive user of mbuto at the moment, so I
got slightly annoyed by the fact it didn't work anymore but I didn't
really investigate further. I used it whenever an initramfs took more than
5-10 seconds to build, and I'd keep forgetting to add stuff.

Note that the help message still describes this mode of operation:

  "Build initramfs image unless an existing one is passed."

and in the "Examples":

	./mbuto -f kata.img zsh_5.6.2-3_amd64.deb
		Install zsh package to pre-existing kata.img

but I also realised it's not convenient to have this as default, because,
especially for initramfs images that can be built faster, one might just
want to rebuild a single binary and the image, repeatedly.

Perhaps, instead of dropping this altogether, we could introduce a new
-K ("keep") option that skips the unconditional wd assignment and calls
cpio_init() (which becomes cpio_load() or something like that).

-- 
Stefano