[PATCH v4 1/2] kexec: Add helper to report an active kexec reboot

[Shradha Gupta <shradhagupta@linux.microsoft.com>]

A shutdown callback in a loadable module may need to distinguish a
kexec reboot from a normal restart, halt, or poweroff. The Hyper-V
VMBus driver needs this distinction when moving its kexec cleanup into
a common syscore shutdown callback.

Add kexec_is_in_progress() and export it to GPL modules so the callback
can remain guarded when VMBus is built as a module. Provide a false
inline implementation when CONFIG_KEXEC_CORE is disabled.

The helper reports only the normal kexec reboot path. Crash kexec and
preserve-context kexec do not set this state.

Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Reviewed-by: Naman Jain <namjain@linux.microsoft.com>
---
 include/linux/kexec.h | 2 ++
 kernel/kexec_core.c   | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 8a22bc9b8c6c..827a5311d97a 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -468,6 +468,7 @@ bool kexec_load_permitted(int kexec_image_type);
 
 /* flag to track if kexec reboot is in progress */
 extern bool kexec_in_progress;
+bool kexec_is_in_progress(void);
 
 #ifndef page_to_boot_pfn
 static inline unsigned long page_to_boot_pfn(struct page *page)
@@ -544,6 +545,7 @@ static inline void *kimage_map_segment(struct kimage *image, int idx)
 { return NULL; }
 static inline void kimage_unmap_segment(void *buffer) { }
 #define kexec_in_progress false
+static inline bool kexec_is_in_progress(void) { return false; }
 #endif /* CONFIG_KEXEC_CORE */
 
 #ifdef CONFIG_KEXEC_SIG
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index dc770b9a6d05..282c7b3c6c35 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -23,6 +23,7 @@
 #include <linux/hardirq.h>
 #include <linux/elf.h>
 #include <linux/elfcore.h>
+#include <linux/export.h>
 #include <linux/utsname.h>
 #include <linux/numa.h>
 #include <linux/suspend.h>
@@ -54,6 +55,12 @@ atomic_t __kexec_lock = ATOMIC_INIT(0);
 /* Flag to indicate we are going to kexec a new kernel */
 bool kexec_in_progress = false;
 
+bool kexec_is_in_progress(void)
+{
+	return kexec_in_progress;
+}
+EXPORT_SYMBOL_GPL(kexec_is_in_progress);
+
 bool kexec_file_dbg_print;
 
 /*
-- 
2.43.0