On 3/9/19 7:11 AM, Greg KH wrote:
There is no licensing issue, see my follow-up comment about that.
It's all in ease-of-use here. You want to build a trace function
against a running kernel, and now you have the header files for that
specific kernel right there in the kernel itself to build against. It
doesn't get easier than that.
Agreed.
It seems that opinions in this thread are split along two conceptions of
a "Linux system". On one side there's that of the conventional "Linux
distro" where the entity generating the distro has full control over the
entire process and the parts thereof. On the other side there's the
world that has evolved out of the multi-party ecosystem that Android
fostered. In the later, there isn't a single party that controls all
aspects of the "distro". Instead, there are a multitude of parties
contributing to creating a fully-functional Linux-based system.
In the latter ecosystem, the kernel and the filesystems (*plural*) used
with it do not necessarily come from the same place, are maintained by
the same parties or even required to be in lock-step. For all I know,
the filesystem images are coming from one party and the kernel is at one
point from one party and at another point can be substituted, possibly
for testing purposes, without userspace images ever changing. No
licensing issues at all involved, either with regards to the headers or
the distribution of the kernel itself, which, in as far as I've seen
when speaking of known industry players (those that matter here), are
always ultimately available in source from somewhere.
Instead the issue is that I want to be able to give user-space access to
the headers that were used to build the kernel that they're running
over, regardless of where this kernel came from. And since I have to
assume that those two parts (kernel vs. user-space) are coming from
separate parties and can be arbitrarily replaced, there needs to be some
form of "contract" between them. The kernel's ABI already provides quite
a bit of that and, as Joel pointed out, Google can enforce a few more
things, such as default kernel configs, to "make things work". But one
option that doesn't exist in the world Android evolves in is to somehow
ensure that the filesystem images somehow have kernel-specific
tool-required artifacts for every possible kernel they may run against.
That's just not possible.
That's especially true in the case of modern-day Android where the final
system is made of at least half a dozen filesystem images with each
image possibly coming from a different party. The /vendor partition
(with the hardware enablement), for example, could be coming from the
device vendor while the /system partition (with the Android framework),
for example, could be coming straight from Google in the form of
"Generic System Image" -- an image meant to run as-is on any
Treble-compliant system. /system might have the tools for eBPF, but
/vendor might have modules, while still the "boot" partition might have
the kernel. There's no reason I can't replace the boot partition
*without* changing /vendor. And there's no reason I can't replace
/vendor *without* replacing the boot partition. And all other
combinations with all other images.
That, in my view, is a big part of the problem Joel's patch solves: in a
system whose functionality requires multiple *independent* parties to
work together, I can still get the necessary kernel headers for
user-space tools to properly operate regardless of which part of the
system id being substituted or replaced.
Cheers,
--
Karim Yaghmour
CEO - Opersys inc. / www.opersys.com
http://twitter.com/karimyaghmour
