On Sun, Apr 12, 2020 at 01:35:07PM +0800, Baoquan He wrote: > 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. All that opinion and hand waving about the benefits of the new interface is totally irrelevent for 32-bit ARM for the reasons I stated in my email to which you replied. Gradual obsolecence or not, the file interface can't be supported on 32-bit ARM as-is - it is totally inadequate and inferior as an API compared to the functionality we have with plain kexec_load. Without that point addressed, kexec_file_load is meaningless for 32-bit ARM. -- 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
