Hi Geert,
On 3/9/19 2:26 PM, Geert Uytterhoeven wrote:
Thanks for the explanation!
Happy this was useful :)
So how does this work, with kernel images and kernel modules supplied
by separate parties, not "bound" by the same kernel headers/API, as they
can be replaced separately?
The thing with Android is that there isn't a "one size fits all". Google
provides guidance, policies and at least one example implementation
through the Pixel lines.
Each vendor however is allowed a great degree of latitude with regards
to what they decide to do. Personally, if I was advising a team working
on an Android device where Joel's patch was available as part of their
kernel I would just recommend that they build it in -- i.e. not as a
module. Hence, there would be no module chasing game.
With regards to Google's guidelines for manufacturers, though, Google
states that CONFIG_MODVERSIONS needs to be enabled, see here:
https://source.android.com/devices/architecture/kernel/modular-kernels
FWIW, that doesn't mean that modules are actually used. Devices don't
necessarily have to be using modules.
Isn't the need for kernel headers for user-space tools something different,
as this is limited to the uapi versions, which are less (almost not) subject
to change, compared to the kernel headers needed for compiling kernel
modules?
Sorry, I should've been clearer. I'm including eBPF/BCC into the
"user-space tools" here. That was in fact my prime motivation in
encouraging Joel at the last LPC to look at this. I've been integrating
the teaching of eBPF into my AOSP debugging and performance analysis
class (see CC courseware here:
http://www.opersys.com/training/android-debug-and-performance), and it
was pretty messy trying to show people how to benefit from such tools
under Android. Joel's present set of patches would obviate this problem.
HTH,
--
Karim Yaghmour
CEO - Opersys inc. / www.opersys.com
http://twitter.com/karimyaghmour
