On 04/11/20 at 10:30am, Russell King - ARM Linux admin wrote: > On Sat, Apr 11, 2020 at 11:44:14AM +0800, Baoquan He wrote: > > Because We tend to use kexec_file_load more and improve/enhance it in the > > future, and gradually obsolete the old kexec_load interface which this > > patchset is trying to fix on. > > That's not going to happen; 32-bit ARM kexec uses the kexec_load > interface rather than the kexec_file_load version, and I see no one > with any interest in changing that - and there's users of the former. > > I don't see how it's possible to convert 32-bit ARM kexec to the > kexec_file_load interface - this assumes that all you have are the > kernel, initrd, and commandline, but on 32-bit ARM kexec, we have > kernel, initrd and the dtb blob which the user can specify. Well, I understand what you said about 32-bit ARM support with only kexec_old support thing. That's why I said we tend to obsolete it 'GRADUALLY'. It's the existing users who are using kexec_load, and the ARCHes which only has kexec_load, make us have to transfer to kexec_file_load gradually. Comparing with kexec_load, kexec_file_load has only one disadvantage, that is some ARCHes only have kexec_load. Otherwise, kexec_file_load benefits kexec/kdump developping/maintaining very much. The loading job of kexec_file_load is mostly done in kernel, we can get whatever we want about kernel information very conveniently to do anything needed. For the kexec_load interface, the loading job is mostly done in userspace, we have to export kernel information to procfs, sysfs, etc, then parse them in kexec_tools, finally passed it to kernel part of kexec loading. The gradual obsoleting means we may only add feature/improvement/enhancement to kexec_file_load. And if a bug fix is needed for both kexec_load and kexec_file_load, and the fix is very complicated, we may only fix it in kexec_file_load too. Kexec_file_load interface is suggested to add if does't have, just port user space part to kernel as x86/s390/arm64 have done. Surely, it doesn't mean we don't fix the critical/blocker bug with kexec_load loading. We still try to do, just are not so eager. In the existing product environment, the kexec_load is used, just keep using it. Do we bother to change it to kexec_file_load, e.g in our RHEL7 distros? Certainly not. But in our new product, we will change to use kexec_file_load interface. I guess this is similar with arm64. The advantage and benefit have been told in the 2nd paragraph. As for 32-bit ARM, is it like the old product, we have many in-use systems deployed in customers' laboratory? Wondering if ARM continues designing new 32-bit ARM cpu, and some companies continue producing tons of 32-bit ARM cpus. If yes, I think we need continue taking care of kexec_load if 32-bit ARM can't convert to kexec_file_load. If not, it may be not a barrier when we consider converting kexec_load to kexec_file_load in other ARCHes. We just need keep using it, try to fix those critical/blocker bug in kexec_load interface if encountered. Finally, comning back to this patchset itself, the issue James spotted is not so ciritical, I would say. When I do kexec jumping, I will do loading firstly, then trigge jumping. I can think of the case that people may load kexec-ed kernel, then do something else, later she/he triggers the kexec jumping. These are not necessary steps. As Dave and I replied to James in the cover-letter thread, adding a systemd service of kexec loading, monitor hotplug uevent, reload it if any hot remove happened. This is quite easy to do, I don't see any problem with it, and why we don't do like this. My personal opinion, please tell if I miss anything. > > So, if we wanted to obsolete the kexec_load interface, _first_ there > needs to be a way to provide users with the existing functionality > they have already in place on 32-bit ARM - otherwise we're looking > at a userspace regression. Especially as kexec_file_load takes > precedence on some distro patched versions of the kexec tool, > irrespective of which interface the user requests of the tool. > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up >
