[Buildroot] [PATCH 2/2] fs/cpio: make cpio rootfs reproducible
Yann E. MORIN
yann.morin.1998 at free.fr
Sun Jul 14 16:47:25 UTC 2019
Atharva, All,
On 2019-07-14 21:53 +0530, Atharva Lele spake thusly:
> Pass the recommended argument in the CPIO manual to make cpio archives
> reproducible.
>
> Reference: https://www.gnu.org/software/cpio/manual/cpio.html#Copy_002dpass-mode
>
> Pre-patch diffoscope output: https://gitlab.com/snippets/1874745
> Post-patch: https://gitlab.com/snippets/1874746
>
> We can see that post-patch, the archive related differences are removed.
> The differences are arising from utils/bin/getconf. This will have to
> be investigated further. However, that is unrelated to cpio.
>
> Signed-off-by: Atharva Lele <itsatharva at gmail.com>
> ---
> Changes v1 -> v2:
> - Added comment
> - Build host-cpio if we are reproducible, reason is --reproducible
> option does not exist prior to cpio 2.12. (suggested by Yann, Arnout)
> ---
> fs/cpio/cpio.mk | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/cpio/cpio.mk b/fs/cpio/cpio.mk
> index 1f0cafe62f..521418f950 100644
> --- a/fs/cpio/cpio.mk
> +++ b/fs/cpio/cpio.mk
> @@ -29,8 +29,16 @@ endif # BR2_ROOTFS_DEVICE_CREATION_STATIC
>
> ROOTFS_CPIO_PRE_GEN_HOOKS += ROOTFS_CPIO_ADD_INIT
>
> +# --repoducible option was not introduced until cpio v2.12. Some distros
> +# like Ubuntu 16.04 or Debian oldstable which package v2.11. Hence build
> +# host-cpio.
> +ifeq ($(BR2_REPRODUCIBLE), y)
> +ROOTFS_CPIO_DEPENDENCIES += host-cpio
> +CPIO_OPTS = --reproducible
Having a pure assignment in a condition is risky for the future. If we
were to later add new unconditional options, we would add them before
this part (as is customary to do: uncoditional stuff goes before
conditional stuff). In this case, the assignment here would override the
uncoditional options, which is not nice.
Instead, I think we prefer an append-assignment in conditional blocks,
even if the variable is not already defined.
Arnout, Thomas, can you confirm/infirm my opinion? ;-)
Otherwise:
Reviewed-by: Yann E. MORIN <yann.morin.1998 at free.fr>
Regards,
Yann E. MORIN.
> +endif
> +
> define ROOTFS_CPIO_CMD
> - cd $(TARGET_DIR) && find . | cpio --quiet -o -H newc > $@
> + cd $(TARGET_DIR) && find . | cpio $(CPIO_OPTS) --quiet -o -H newc > $@
> endef
>
> ifeq ($(BR2_TARGET_ROOTFS_CPIO_UIMAGE),y)
> --
> 2.22.0
>
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