linux-kernel - Re: [External] Re: [PATCH] misc: pvpanic: add crash loaded event

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Date:   Thu, 12 Dec 2019 14:35:39 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     zhenwei pi <pizhenwei@...edance.com>
Cc:     arnd@...db.de, peng.hao2@....com.cn, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] misc: pvpanic: add crash loaded event

On Thu, Dec 12, 2019 at 09:26:22PM +0800, zhenwei pi wrote:
> On 12/12/19 9:01 PM, Greg KH wrote:
> 
> > On Thu, Dec 12, 2019 at 08:32:26PM +0800, zhenwei pi wrote:
> > > Some users prefer kdump tools to generate guest kernel dumpfile,
> > > at the same time, need a out-of-band kernel panic event.
> > > 
> > > Currently if booting guest kernel with 'crash_kexec_post_notifiers',
> > > QEMU will recieve PVPANIC_PANICKED event and stop VM. If booting
> > > guest kernel without 'crash_kexec_post_notifiers', guest will not
> > > call notifier chain.
> > > 
> > > Add PVPANIC_CRASH_LOADED bit for pvpanic event, it means that guest
> > > actually hit a kernel panic, but kernel wants to handle by itself.
> > > 
> > > Signed-off-by: zhenwei pi <pizhenwei@...edance.com>
> > > ---
> > >   drivers/misc/pvpanic.c | 10 +++++++++-
> > >   1 file changed, 9 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/misc/pvpanic.c b/drivers/misc/pvpanic.c
> > > index 95ff7c5a1dfb..a8cc96c90550 100644
> > > --- a/drivers/misc/pvpanic.c
> > > +++ b/drivers/misc/pvpanic.c
> > > @@ -10,6 +10,7 @@
> > >   #include <linux/acpi.h>
> > >   #include <linux/kernel.h>
> > > +#include <linux/kexec.h>
> > >   #include <linux/module.h>
> > >   #include <linux/of.h>
> > >   #include <linux/of_address.h>
> > > @@ -19,6 +20,7 @@
> > >   static void __iomem *base;
> > >   #define PVPANIC_PANICKED        (1 << 0)
> > > +#define PVPANIC_CRASH_LOADED    (1 << 1)
> > BIT(1)?
> 
> zhenwei: yes, define PVPANIC_CRASH_LOADED as BIT(1)?
> 
> > 
> > >   MODULE_AUTHOR("Hu Tao <hutao@...fujitsu.com>");
> > >   MODULE_DESCRIPTION("pvpanic device driver");
> > > @@ -34,7 +36,13 @@ static int
> > >   pvpanic_panic_notify(struct notifier_block *nb, unsigned long code,
> > >   		     void *unused)
> > >   {
> > > -	pvpanic_send_event(PVPANIC_PANICKED);
> > > +	unsigned int event = PVPANIC_PANICKED;
> > > +
> > > +	if (kexec_crash_loaded())
> > > +		event = PVPANIC_CRASH_LOADED;
> > > +
> > > +	pvpanic_send_event(event);
> > Who gets this event to know that the above new bit is set or not?
> 
> Hypervisor will catch this event. A typical case maybe like this: guest os triggers
> pvpanic PVPANIC_CRASH_LOADED event, QEMU gets this event by handling vm-exit reason,
> then QEMU posts event to libvirt. Monotor agent gets domain lifecycle event from
> libvirt. Bingo, we can know that the guest has crashed but it handle error by
> kexec crash loaded image.

But as you have burried this user api value in a random .c file, how
does anything outside of the kernel know what the value really is for?

Shouldn't the #define be in a uapi file?

thanks,

greg k-h-