[Buildroot] [PATCH 2/2] i2c-tools: Adds check of i2c kernel option

[Denis Thulin]

Hi Thomas,

----- Mail original -----
> Hello,
> 
> On Tue,  4 Aug 2015 14:27:07 +0200, Denis THULIN wrote:
> 
> > +I2C_TOOLS_DEPENDENCIES += linux
> 
> This is not acceptable: we want to allow people to build just a
> rootfs,
> and not necessarily the Linux kernel with Buildroot. I personally use
> Buildroot a lot to build a small initramfs that I then bundle in my
> kernel image, which is built separately from Buildroot (because I'm
> doing kernel development, so I build the kernel myself).

Oops. I had not thought of that.

I understand that this is a mistake for kernel options.
But could patch [1/2] be useful for the other kconfig packages ?
I think it would be useful to know options of busybox when building
packages.

> 
> Also, this is going completely backwards compared to what we've been
> doing until now. Currently, in linux/linux.mk, we have some logic to
> make sure a number of kernel options are enabled when certain
> Buildroot
> packages are enabled:
> 
>         $(if $(BR2_PACKAGE_KTAP),
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_DEBUG_FS,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_ENABLE_DEFAULT_TRACERS,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_PERF_EVENTS,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_FUNCTION_TRACER,$(@D)/.config))
>         $(if $(BR2_PACKAGE_SYSTEMD),
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_CGROUPS,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_INOTIFY_USER,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_FHANDLE,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_AUTOFS4_FS,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_TMPFS_POSIX_ACL,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_TMPFS_POSIX_XATTR,$(@D)/.config))
>         $(if $(BR2_PACKAGE_SMACK),
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_SECURITY,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_SECURITY_SMACK,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_SECURITY_NETWORK,$(@D)/.config))
>         $(if $(BR2_PACKAGE_IPTABLES),
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_IP_NF_IPTABLES,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_IP_NF_FILTER,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_NETFILTER,$(@D)/.config)
>                 $(call
>                 KCONFIG_ENABLE_OPT,CONFIG_NETFILTER_XTABLES,$(@D)/.config))
> 
> However, we generally do this only when enabling the kernel option in
> question is needed to get the package to *build*. When it is
> necessary
> to make the thing run properly, or when the dependency is really
> obvious, we simply don't handle this.

Would it not be a better thing for all packages to provide a list
of kernel options they need and for LINUX_KCONFIG_FIXUP_CMDS
to select those options rather than using lots of if blocks ?

That list could also be exported so that people using a custom kernel
would know which options Buildroot would have selected had they used
the default kernel.

If it is a better thing to do, I could try to implement that,
if time allows.

Best regards,

Denis

> 
> So for example in your case, it is completely obvious that i2c-tools
> needs I2C support in the kernel, otherwise it's a tool that is quite
> useless.
> 
> Best regards,
> 
> Thomas
> --
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com
>