On January 20, 2019 5:45:53 PM PST, Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: >On Sun, Jan 20, 2019 at 01:58:15PM -0800, hpa@xxxxxxxxx wrote: >> On January 20, 2019 8:10:03 AM PST, Joel Fernandes ><joel@xxxxxxxxxxxxxxxxx> wrote: >> >On Sat, Jan 19, 2019 at 11:01:13PM -0800, hpa@xxxxxxxxx wrote: >> >> On January 19, 2019 2:36:06 AM PST, Greg KH >> ><gregkh@xxxxxxxxxxxxxxxxxxx> wrote: >> >> >On Sat, Jan 19, 2019 at 02:28:00AM -0800, Christoph Hellwig >wrote: >> >> >> This seems like a pretty horrible idea and waste of kernel >memory. >> >> > >> >> >It's only a waste if you want it to be a waste, i.e. if you load >the >> >> >kernel module. >> >> > >> >> >This really isn't any different from how /proc/config.gz works. >> >> > >> >> >> Just add support to kbuild to store a compressed archive in >> >initramfs >> >> >> and unpack it in the right place. >> >> > >> >> >I think the issue is that some devices do not use initramfs, or >> >switch >> >> >away from it after init happens or something like that. Joel has >> >all >> >> >of >> >> >the looney details that he can provide. >> >> > >> >> >thanks, >> >> > >> >> >greg k-h >> >> >> >> Yeah, well... but it is kind of a losing game... the more >in-kernel >> >stuff there is the less smiley are things to actually be supported. >> > >> >It is better than nothing, and if this makes things a bit easier and >> >solves >> >real-world issues people have been having, and is optional, then I >> >don't see >> >why not. >> > >> >> Modularizing is it in some ways even crazier in the sense that at >> >that point you are relying on the filesystem containing the module, >> >which has to be loaded into the kernel by a root user. One could >even >> >wonder if a better way to do this would be to have "make >> >modules_install" park an archive file – or even a directory as >opposed >> >to a symlink – with this stuff in /lib/modules. We could even >provide a >> >tmpfs shim which autoloads such an archive via the firmware loader; >> >this might even be generically useful, who knows. >> > >> >All this seems to assume where the modules are located. In Android, >we >> >don't >> >have /lib/modules. This patch generically fits into the grand scheme >> >things >> >and I think is just better made a part of the kernel since it is not >> >that >> >huge once compressed, as Dan also pointed. The more complex, and the >> >more >> >assumptions we make, the less likely people writing tools will get >it >> >right >> >and be able to easily use it. >> > >> >> >> >> Note also that initramfs contents can be built into the kernel. >> >Extracting such content into a single-instance tmpfs would again be >a >> >possibility >> > >> >Such an approach would bloat the kernel image size though, which may >> >not work >> >for everyone. The module based approach, on the other hand, gives an >> >option >> >to the user to enable the feature, but not have it loaded into >memory >> >or used >> >until it is really needed. >> > >> >thanks, >> > >> > - Joel >> >> Well, where are the modules? They must exist in the filesystem. > >The scheme of loading a module doesn't depend on _where_ the module is >on the >filesystem. As long as a distro knows how to load a module in its own >way (by >looking into whichever paths it cares about), that's all that matters. >And >the module contains compressed headers which saves space, vs storing it >uncompressed on the file system. > >To remove complete reliance on the filesystem, there is an option of >not >building it as a module, and making it as a built-in. > >I think I see your point now - you're saying if its built-in, then it >becomes kernel memory that is lost and unswappable. Did I get that >right? >I am saying that if that's a major concern, then: >1. Don't make it a built-in, make it a module. >2. Don't enable it at for your distro, and use a linux-headers package >or >whatever else you have been using so far that works for you. > >thanks, > > - Joel My point is that if we're going to actually solve a problem, we need to make it so that the distro won't just disable it anyway, and it ought to be something scalable; otherwise nothing is gained. I am *not* disagreeing with the problem statement! Now, /proc isn't something that will autoload modules. A filesystem *will*, although you need to be able to mount it; furthermore, it makes it trivially to extend it (and the firmware interface provides an . easy way to feed the data to such a filesystem without having to muck with anything magic.) Heck, we could even make it a squashfs image that can just be mounted. So, first of all, where does Android keep its modules, and what is actually included? Is /sbin/modprobe used to load the modules, as is normal? We might even be able to address this with some fairly trivial enhancements to modprobe; specifically to search in the module paths for something that isn't a module per se. The best scenario would be if we could simply have the tools find the location equivalent of /lib/modules/$version/source... -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
