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[PATCH 1/2] Add a kexec_crash_loaded() function

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  [PATCH 1/2] Add a kexec_crash_loaded() function Petr Tesarik <ptesarik@suse.com> - 2016-07-13 14:30 +0200
    Re: [PATCH 1/2] Add a kexec_crash_loaded() function Josh Triplett <josh@joshtriplett.org> - 2016-07-13 15:00 +0200
      Re: [PATCH 1/2] Add a kexec_crash_loaded() function Petr Tesarik <ptesarik@suse.com> - 2016-07-13 15:10 +0200

#1442394 — [PATCH 1/2] Add a kexec_crash_loaded() function

Provide a wrapper function to be used by kernel code to check whether
a crash kernel is loaded. It returns the same value that can be seen
in /sys/kernel/kexec_crash_loaded by userspace programs.

I'm exporting the function, because it will be used by Xen, and it is
possible to compile Xen modules separately to enable the use of PV
drivers with unmodified bare-metal kernels.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 include/linux/kexec.h |    2 ++
 kernel/kexec_core.c   |    6 ++++++
 kernel/ksysfs.c       |    2 +-
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index e8acb2b..d461d02 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -228,6 +228,7 @@ extern void *kexec_purgatory_get_symbol_addr(struct kimage *image,
 extern void __crash_kexec(struct pt_regs *);
 extern void crash_kexec(struct pt_regs *);
 int kexec_should_crash(struct task_struct *);
+int kexec_crash_loaded(void);
 void crash_save_cpu(struct pt_regs *regs, int cpu);
 void crash_save_vmcoreinfo(void);
 void arch_crash_save_vmcoreinfo(void);
@@ -324,6 +325,7 @@ struct task_struct;
 static inline void __crash_kexec(struct pt_regs *regs) { }
 static inline void crash_kexec(struct pt_regs *regs) { }
 static inline int kexec_should_crash(struct task_struct *p) { return 0; }
+static inline int kexec_crash_loaded(void) { return 0; }
 #define kexec_in_progress false
 #endif /* CONFIG_KEXEC_CORE */
 
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 56b3ed0..a303dce 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -95,6 +95,12 @@ int kexec_should_crash(struct task_struct *p)
 	return 0;
 }
 
+int kexec_crash_loaded(void)
+{
+	return !!kexec_crash_image;
+}
+EXPORT_SYMBOL_GPL(kexec_crash_loaded);
+
 /*
  * When kexec transitions to the new kernel there is a one-to-one
  * mapping between physical and virtual addresses.  On processors
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 152da4a..bf9fc9d 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -101,7 +101,7 @@ KERNEL_ATTR_RO(kexec_loaded);
 static ssize_t kexec_crash_loaded_show(struct kobject *kobj,
 				       struct kobj_attribute *attr, char *buf)
 {
-	return sprintf(buf, "%d\n", !!kexec_crash_image);
+	return sprintf(buf, "%d\n", kexec_crash_loaded());
 }
 KERNEL_ATTR_RO(kexec_crash_loaded);
 

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#1442423

On Wed, Jul 13, 2016 at 02:19:55PM +0200, Petr Tesarik wrote:
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -95,6 +95,12 @@ int kexec_should_crash(struct task_struct *p)
>  	return 0;
>  }
>  
> +int kexec_crash_loaded(void)
> +{
> +	return !!kexec_crash_image;
> +}

Nit: this function should return bool rather than int, since it
effectively returns true/false.

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#1442435

On Wed, 13 Jul 2016 05:52:33 -0700
Josh Triplett <josh@joshtriplett.org> wrote:

> On Wed, Jul 13, 2016 at 02:19:55PM +0200, Petr Tesarik wrote:
> > --- a/kernel/kexec_core.c
> > +++ b/kernel/kexec_core.c
> > @@ -95,6 +95,12 @@ int kexec_should_crash(struct task_struct *p)
> >  	return 0;
> >  }
> >  
> > +int kexec_crash_loaded(void)
> > +{
> > +	return !!kexec_crash_image;
> > +}
> 
> Nit: this function should return bool rather than int, since it
> effectively returns true/false.

I thought about this for a moment. Since the return value should also
be used for the corresponding sysctl, which is an integer, I wasn't
sure if bool is the correct type, especially since other boolean
functions in kexec.h also return int... But that could be legacy.

I've got no problem changing the type to 'bool' if that's what it takes.

Petr T

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