Messages in this thread | | | From | Rob Herring <> | Date | Fri, 20 Nov 2020 07:50:29 -0600 | Subject | Re: [PATCH 0/2] arm64: Implement CONFIG_CMDLINE_EXTEND |
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On Thu, Nov 5, 2020 at 9:28 AM Tyler Hicks <tyhicks@linux.microsoft.com> wrote: > > On 2020-11-05 09:58:54, Will Deacon wrote: > > On Wed, Nov 04, 2020 at 11:40:09PM -0600, Tyler Hicks wrote: > > > On 2020-11-04 12:08:12, Will Deacon wrote: > > > > On Tue, Nov 03, 2020 at 09:59:52AM -0600, Tyler Hicks wrote: > > > > > On 2020-09-21 14:15:55, Tyler Hicks wrote: > > > > > > Provide the CONFIG_CMDLINE_EXTEND config option for arm64 kernels. This > > > > > > config option can be used to extend the kernel command line parameters, > > > > > > specified by the bootloader, with additional command line parameters > > > > > > specified in the kernel configuration. > > > > > > > > > > Hi Catalin and Will - Friendly ping on this series now that we're > > > > > on the other side of the 5.10 merge window. I hope it can be considered > > > > > for 5.10+1. Let me know if I need to rebase/resubmit. Thanks! > > > > > > > > Can you use bootconfig to achieve what you need? > > > > > > Thanks for mentioning bootconfig. I hadn't considered it. > > > > > > After reading the docs and code, I see a few reasons why I can't use it > > > out of the box: > > > > > > 1) It requires "bootconfig" to be appended to the kernel command line. > > > My proposed patch series makes it possible to append new options to > > > the kernel command line in situations where the bootloader is not > > > interactive. This presents a circular dependency problem for my use > > > case. > > > > > > A new config option could be added to force the enablement of > > > bootconfig but that would sort of be a single-use duplicate of > > > CONFIG_CMDLINE_EXTEND's functionality. > > > > > > 2) Not all kernel command line options can be configured using > > > bootconfig. For example, the "nokaslr" and "crashkernel=" parameters > > > are parsed/handled before setup_boot_config() is called. KASLR can > > > be disabled via a kernel config change but there's no config option > > > equivalent for "crashkernel=". Changing the "crashkernel=" command > > > line option is something that I need to support because a > > > development/debug kernel build often requires a larger reservation > > > and we find ourselves adjusting the "crashkernel=" value fairly > > > often. > > > > > > 3) External FIT image build systems do not yet support bootconfig since > > > it is so new. It is completely fair if you file this away in your > > > not-my-problem folder but simple kernel config modifications, as > > > needed for CONFIG_CMDLINE_EXTEND, are something that every image > > > build system is likely to support today. > > > > > > All that said, I do really like the look of bootconfig. Unfortunately, > > > it doesn't let me achieve everything I need. > > > > Ok, well thanks for having a look. A follow-up question I have is how is > > this handled on x86? They don't appear to have CONFIG_CMDLINE_EXTEND either > > afaict. Is it because their bootloader story tends to be more uniform? > > x86's equivalent was implemented by commit 516cbf3730c4 ("x86, bootup: > add built-in kernel command line for x86 (v2)"). To summarize, you have > to enable CONFIG_CMDLINE_BOOL and then that lets you define built-in > command line parameters in CONFIG_CMDLINE. However, it is backwards in > that the command line provided by the bootloader is appended onto the > end of CONFIG_CMDLINE. > > This doesn't seem as useful to me because, using the crashkernel= > example from above, the bootloader provided crashkernel= value may need > to be overridden by the built-in command line to provide a different > crashkernel= value for the particular kernel build being booted. Most > kernel command line parameter parsers are implemented in a way that > supports multiple instances of the parameter while only honoring the > last instance.
These config options should be common IMO. It's a minefield though. You might want to look at this prior attempt[1].
Rob
[1] https://lore.kernel.org/lkml/20190319232448.45964-2-danielwa@cisco.com/
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