linux-kernel - Re: [PATCH] initramfs: Fix initramfs rebuilds w/ compression after disabling

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Date:   Fri, 29 Sep 2017 20:42:26 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Francisco Blas Izquierdo Riera (klondike)" <klondike@...ndike.es>,
        Nicholas Piggin <npiggin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] initramfs: Fix initramfs rebuilds w/ compression after
 disabling



On 09/29/2017 08:39 PM, Florian Fainelli wrote:
> This is a follow-up to commit 57ddfdaa9a72 ("initramfs: fix disabling of
> initramfs (and its compression)"). This particular commit fixed the use case
> where we build the kernel with an initramfs with no compression, and then we
> build the kernel with no initramfs.
> 
> Now this still left us with the same case as described here:
> http://lkml.kernel.org/r/20170521033337.6197-1-f.fainelli@gmail.com
> not working with initramfs compression. This can be seen by the following
> steps/timestamps:
> 
> https://www.spinics.net/lists/kernel/msg2598153.html
> 
> .initramfs_data.cpio.gz.cmd is correct:
> 
> cmd_usr/initramfs_data.cpio.gz := /bin/bash
> ./scripts/gen_initramfs_list.sh -o usr/initramfs_data.cpio.gz  -u 1000
> -g 1000  /home/fainelli/work/uclinux-rootfs/romfs
> /home/fainelli/work/uclinux-rootfs/misc/initramfs.dev
> 
> and was generated the first time we did generate the gzip initramfs, so the
> command has not changed, nor its arguments, so we just don't call it, no
> initramfs cpio is re-generated as a consequence.
> 
> The fix for this problem is just to properly keep track of the
> .initramfs_cpio_data.d file by suffixing it with the compression extension.
> This takes care of properly tracking dependencies such that the initramfs get
> (re)generated any time files are added/deleted etc.
> 
> Fixes: db2aa7fd15e8 ("initramfs: allow again choice of the embedded initramfs compression algorithm")
> Fixes: 9e3596b0c653 ("kbuild: initramfs cleanup, set target from Kconfig")
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---

Nick, thanks a lot for your patience and help on the other thread! At
some point I did mention that I was wondering if this would cause
systematic rebuilds of the compressed initramfs, but after more testing,
it does not, things now work as expected again (until next time ;) ).

>  usr/Makefile | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/usr/Makefile b/usr/Makefile
> index 0b87e71c00fc..2d7d7f4b91f1 100644
> --- a/usr/Makefile
> +++ b/usr/Makefile
> @@ -7,6 +7,7 @@ PHONY += klibcdirs
>  
>  suffix_y = $(subst $\",,$(CONFIG_INITRAMFS_COMPRESSION))
>  datafile_y = initramfs_data.cpio$(suffix_y)
> +datafile_d_y = .$(datafile_y).d
>  AFLAGS_initramfs_data.o += -DINITRAMFS_IMAGE="usr/$(datafile_y)"
>  
>  
> @@ -29,12 +30,12 @@ ramfs-args  := \
>          $(if $(CONFIG_INITRAMFS_ROOT_UID), -u $(CONFIG_INITRAMFS_ROOT_UID)) \
>          $(if $(CONFIG_INITRAMFS_ROOT_GID), -g $(CONFIG_INITRAMFS_ROOT_GID))
>  
> -# .initramfs_data.cpio.d is used to identify all files included
> +# $(datafile_d_y) is used to identify all files included
>  # in initramfs and to detect if any files are added/removed.
>  # Removed files are identified by directory timestamp being updated
>  # The dependency list is generated by gen_initramfs.sh -l
> -ifneq ($(wildcard $(obj)/.initramfs_data.cpio.d),)
> -	include $(obj)/.initramfs_data.cpio.d
> +ifneq ($(wildcard $(obj)/$(datafile_d_y)),)
> +	include $(obj)/$(datafile_d_y)
>  endif
>  
>  quiet_cmd_initfs = GEN     $@
> @@ -52,5 +53,5 @@ $(deps_initramfs): klibcdirs
>  # 3) If gen_init_cpio are newer than initramfs_data.cpio
>  # 4) arguments to gen_initramfs.sh changes
>  $(obj)/$(datafile_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
> -	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/.initramfs_data.cpio.d
> +	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/$(datafile_d_y)
>  	$(call if_changed,initfs)
> 

-- 
Florian