On 13-11-22 06:05 AM, Paul Eggleton wrote:
Hi Darren,
On Thursday 21 November 2013 18:47:07 Hart, Darren wrote:
Regarding the following 2 bugs:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=5574
Add kernel version / configuration check mechanism
and
https://bugzilla.yoctoproject.org/show_bug.cgi?id=2267
Integrate DISTRO_FEATURES with KERNEL_FEATURES
There is a need to reduce errors where a DISTRO config might break due
to lack of kernel support, things such as systemd. There is also
interest in enabling certain kernel features based on
DISTRO/MACHINE_FEATURES, such as wifi.
Neither of these should depend on the Kernel Version as even with the
right version, if the CONFIG_* feature is missing, the image will not
work correctly. There is also the risk of false negatives when a feature
has been backported to a kernel version that didn't have the feature
previously.
Right; I hadn't appreciated this when I wrote the bug but we definitely don't
want to be checking versions.
The recommended approach would be to check for the required CONFIG_*
options after the linux-yocto configuration stage.
There is also the topic of DISTRO_FEATURES ~= "wifi" impacting how the
kernel will be built. The MACHINE should have some say in how this is
done - if the machine can never have wifi, building wifi into the kernel
doesn't make a lot of sense. Something like the following might make
sense:
for FEATURE in DISTRO_FEATURES:
if MACHINE_FEATURES contains FEATURES:
KERNEL_FEATURES += FEATURE_override
Where FEATURE_override is defined something like this:
FEATURE = FEATURE_default
if exists FEATURE_distro:
FEATURE = FEATURE_distro
if exists FEATURE_machine:
FEATURE = FEATURE_machine
There are a couple of slight quirks here:
1) Not all features match up between DISTRO_FEATURES and MACHINE_FEATURES like
this, just a select list. (This is why we currently have COMBINED_FEATURES.)
2) There is some handling in packagegroup-base.bbclass to enable
wifi/bluetooth/3g/nfc functionality in userspace if these features are *not* in
MACHINE_FEATURES but they are in DISTRO_FEATURES *and* MACHINE_FEATURES
indicates some means of expansion exists e.g. pci, pcmcia, usbhost. Whether we
want to try to support this at the kernel level I don't know.
This is effectively a fragment name which needs to be provided by the
linux-yocto kernel meta data as it will be kernel version dependent.
The linkage I'm not sure about is how to know what to test for in the
kernel.bbclass without intimate knowledge of the kernel version CONFIG
options in recipe space.
So are you convinced you want to try to solve these two with one solution in
kernel.bbclass rather than giving individual recipes some easy methods of
checking kernel config options? I agree they are related, but I had imagined
Darren and I have talked about this at length, and there's a balance to
be struck. If you are supporting a multi board/card/soc/arch system
that upgrades over time, you absolutely don't want to spray knowledge
of individual kernel config options around layers and recipes. I've
lived this and wouldn't wish it on anyone again.
A little bit of abstraction into "useful" names and having a mechanism
to map those names to the options specified by particular board's
kernel config actually provides is one part since you'll know on the
front end if you've asked for something that the board can't support.
And then having a query interface or automatic check (the kconf check
can do this already) for options that didn't make the final config, is
a good second check of the whole process.
that we'd solve them both and solve them separately; only doing the feature
map when we're building the kernel still leaves us with recipes like udev that
aren't controlled by a specific feature but do still have kernel config
requirements (of course, you could just assume that if you're using sysvinit
then you're using udev and handle the issue that way, but that seems like a
hack to me).
You still want to avoid some sort of "distributed" kernel policy, with
too much knowledge in each and every recipe, it really does need to be
another "requires and provides" sort of interface for these recipes to
get what they need in a kernel config.
I can't say that I addressed what you were asking directly, but I thought
I'd drop in with some experience and extra context :)
Cheers,
Bruce
Cheers,
Paul
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