Hi Joel, On Thu, 28 Feb 2019 22:26:11 -0500 Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > On Fri, Mar 01, 2019 at 11:28:26AM +0900, Masami Hiramatsu wrote: > > Hi Joel, > > Hi Masami, > > > On Thu, 28 Feb 2019 10:00:54 -0500 > > Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > > > > > > Hmm, isn't it easier to add kernel-headers package on Android? > > > > > > I have already been down that road. In the Android ecosystem, the Android > > > teams only provide a "userspace system image" which goes on the system > > > partition of the flash (and a couple other images are also provided but > > > system is the main one). The system image cannot contain GPL source code. It > > > is also not possible to put kernel headers for every kernel version on the > > > system images that ship and is not practical. Android boots on 1000s of forked > > > kernels. It does not make sense to provide headers on the system image for > > > every kernel version and I already had many discussions on the subject with > > > the teams, it is something that is just not done. Now for kernel modules, > > > there's another image called the "vendor image" which is flashed onto the > > > vendor parition, this is where kernel modules go. This vendor image is not > > > provided by Google for non-Pixel devices. So we have no control over what > > > goes there BUT we do know that kernel modules that are enabled will go there, > > > and we do have control over enforcing that certain kernel modules should be > > > built and available as they are mandatory for Android to function properly. > > > We would also possibly make it a built-in option as well. Anyway my point is > > > keeping it in the kernel is really the easiest and the smartest choice IMO. > > > > Sorry, I'm not convinced yet. This sounds like "because Android decided not > > to put the header files on vendor partition, but kernel module is OK" > > Why don't google ask vendors to put their kernel headers (or header tarball) > > on vendor partition instead? > > May be Google can do that, but I think you missed the point of the patches. > Making it a module is not mandatory, people can build it into the kernel as > well (CONFIG_IKHEADERS_PROC=y). In this case, the proc entry will be > available on boot without any dependency on the filesystem. If you go through > the other threads such as folks from ARM who replied, they just boot a kernel > image for debug purpose and want headers on device available without any > additional step of copying headers to the filesystem. And folks from Google > also said that they wanted a built-in option. Agreed. Making it built-in is reasonable, since it will not involves any other files. :) > There are many usecases for this, I have often run into issues with Linux > over the years not only with Android, but other distros, where I boot custom > kernels with no linux-headers package. This is quite painful. It is > convenient to have it as /proc file since the file is dependent on kernel > being booted up and this will work across all Linux distros and systems. I > feel that if you can keep an open mind about it, you will see that a lot of > people will use this feature if it is accepted and there is a lot of positive > feedback in earlier posts of this set. I don't complain about having headers for custom boot kernel. I agree with you that having kernel headers for debugging is always good. :) So google recommends built-in, it is reasonable. > > > > > The code to read the headers is based on /proc/config.gz code and uses > > > > > the same technique to embed the headers. > > > > > > > > > > To build a module, the below steps have been tested on an x86 machine: > > > > > modprobe kheaders > > > > > rm -rf $HOME/headers > > > > > mkdir -p $HOME/headers > > > > > tar -xvf /proc/kheaders.tar.xz -C $HOME/headers >/dev/null > > > > > cd my-kernel-module > > > > > make -C $HOME/headers M=$(pwd) modules > > > > > rmmod kheaders > > > > > > > > It seems a bit complex, but no difference from compared with carrying > > > > kheaders.tar.gz. I think we would better have a psudo filesystem > > > > which can mount this compressed header file directly :) Then it becomes > > > > simpler, like > > > > > > > > modprobe headerfs > > > > mkdir $HOME/headers > > > > mount -t headerfs $HOME/headers > > > > > > > > And this doesn't consume any disk-space. > > > > > > I felt using a compressed tar is really the easiest way because of all the > > > tools are already available. > > > > As I asked above, if the pure tarball is useful, you can simply ask vendors > > to put the header tarball on their vendor directory. I feel making it as > > a module is not a right way. > > I don't see what is the drawback of making it a module, it makes it well > integrated into kernel build and ecosystem. I also didn't see any > justification you're providing about why it cannot be a module. If you go > through this and earlier threads, a lot of people are Ok with having a module > option. And I asked several top kernel maintainers at LPC and many people > suggested having it as a module. I meant, if we have a tarball, we don't need any operation of loading/unloading kmodules. But if we have this as built-in, yes, this would be much easier to deploy it to device. Anyway, having that option (make it as a module) is not bad. IMHO, that may be more complicated than just have a tarball file, but it is a user's choice. OK, now I understand it. > > > There isn't a compressed in-ram filesystem right > > > now that I'm aware off that can achieve the kind of high compression ratio > > > this patchset does. > > > > I think if linux can support something like tarfs(or compressed initramfs) > > in kernel, it gives linux an improvement not only a hack. :-) > > Agreed, that sounds like a good idea. I will consider doing it once the > series in its current form can be accepted. I am saying so since this series > is simple, and I can do that as a next step since that idea will take a lot > of time to implement. But I am keen on doing it. I look forward to it :-) Thank you! -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
