On Fri, Nov 13, 2020 at 9:06 PM Petr Mladek <pmla...@suse.com> wrote: > > On Fri 2020-11-13 03:58:49, Matteo Croce wrote: > > On Fri, Nov 13, 2020 at 3:46 AM Andrew Morton <a...@linux-foundation.org> > > wrote: > > > > > > On Fri, 13 Nov 2020 02:38:18 +0100 Matteo Croce > > > <mcr...@linux.microsoft.com> wrote: > > > > > > > At this point, since 'pci' enables BOOT_CF9_FORCE type and > > > > BOOT_CF9_SAFE is not user selectable, should I simply leave only > > > > 'pci'? > > > > > > > > This way, we'll have the same set of options for both sysfs and kernel > > > > cmdline. > > > > > > Well, you're the reboot expert ;) > > > > > > > So honored! :) > > > > > But my $0.02 is yes, let's keep the command-line and sysfs interfaces > > > in sync and cover it all in documentation. It would of course be > > > problematic to change the existing reboot= interface. > > > > > > I assume that means doing this? > > > > > > - #define BOOT_CF9_FORCE_STR "cf9_force" > > > + #define BOOT_CF9_FORCE_STR "pci" > > > - #define BOOT_CF9_SAFE_STR "cf9_safe" > > > > Either BOOT_PCI_STR or BOOT_CF9_FORCE_STR, I have no strong preference. > > > > The syntax is 'pci' while the enum BOOT_CF9_FORCE, so we can't please both. > > The question is whether we should modify/allow to set these values at > all. > > Anyway, we must prevent them on non-x86 architectures because > the reboot behavior would be undefined there. They could probably > make a mess even on many x86-architectures. >
That's right, but the same can be obtained by passing 'reboot=pci' on non x86 machines: the cmdline parsing is generic and will set reboot_type on all arches. > I have to admit it has become much more complicated than I thought. > It brings back Andrew's original question whether this interface is > really needed. Are you going to use in the real life? > Yes, there are some cases. Not to mention complex use cases like let persist some memory regions, or change the page size, if a network driver fails to rmmod with the infamous "unregistered_netdevice: waiting for wlan0 to become free", enabling force on the fly allows to reboot the machine. > The interface might do more harm then good when it allows to set > reboot_type that is not normally accessible or disable it when > it is strictly needed. > I looked at the reboot_type usage, there isn't any reference outside arch/x86. In fact, the parameter is just ignored: # uname -m aarch64 # cat /proc/cmdline console=ttyS0,115200n8 reboot=pci # reboot -ff Rebooting. [ 43.893833] reboot: Restarting system The same applies for reboot_force, the only flags available on different architectures are reboot_mode and reboot_cpu. We could hide some handlers for some architectures. We save some space, and avoid letting the user set flags which do nothing. > Anyway, we should get input from some x86-experts about the BOOT_CF9 > values. > Sure, x...@kernel.org ? Regards, -- per aspera ad upstream