[PATCH] Add a sysfs file to determine if a kexec kernel is loaded

Create two files in /sys/kernel, kexec_loaded and kexec_crash_loaded.  Each
file contains a simple boolean value indicating whether the relevant kernel
has been loaded into memory.  The motivation for this is geared around
support.
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/kexec.h

@@ -106,6 +106,7 @@ extern struct page *kimage_alloc_control_pages(struct kimage *image,
 extern void crash_kexec(struct pt_regs *);
 int kexec_should_crash(struct task_struct *);
 extern struct kimage *kexec_image;
+extern struct kimage *kexec_crash_image;
 
 #define KEXEC_ON_CRASH  0x00000001
 #define KEXEC_ARCH_MASK 0xffff0000

kernel/kexec.c

@@ -902,14 +902,14 @@ static int kimage_load_segment(struct kimage *image,
  * kexec does not sync, or unmount filesystems so if you need
  * that to happen you need to do that yourself.
  */
-struct kimage *kexec_image = NULL;
-static struct kimage *kexec_crash_image = NULL;
+struct kimage *kexec_image;
+struct kimage *kexec_crash_image;
 /*
  * A home grown binary mutex.
  * Nothing can wait so this mutex is safe to use
  * in interrupt context :)
  */
-static int kexec_lock = 0;
+static int kexec_lock;
 
 asmlinkage long sys_kexec_load(unsigned long entry, unsigned long nr_segments,
 				struct kexec_segment __user *segments,

kernel/ksysfs.c

@@ -14,6 +14,7 @@
 #include <linux/sysfs.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <linux/kexec.h>
 
 #define KERNEL_ATTR_RO(_name) \
 static struct subsys_attribute _name##_attr = __ATTR_RO(_name)
@@ -48,6 +49,20 @@ static ssize_t uevent_helper_store(struct subsystem *subsys, const char *page, s
 KERNEL_ATTR_RW(uevent_helper);
 #endif
 
+#ifdef CONFIG_KEXEC
+static ssize_t kexec_loaded_show(struct subsystem *subsys, char *page)
+{
+	return sprintf(page, "%d\n", !!kexec_image);
+}
+KERNEL_ATTR_RO(kexec_loaded);
+
+static ssize_t kexec_crash_loaded_show(struct subsystem *subsys, char *page)
+{
+	return sprintf(page, "%d\n", !!kexec_crash_image);
+}
+KERNEL_ATTR_RO(kexec_crash_loaded);
+#endif /* CONFIG_KEXEC */
+
 decl_subsys(kernel, NULL, NULL);
 EXPORT_SYMBOL_GPL(kernel_subsys);
 
@@ -55,6 +70,10 @@ static struct attribute * kernel_attrs[] = {
 #if defined(CONFIG_HOTPLUG) && defined(CONFIG_NET)
 	&uevent_seqnum_attr.attr,
 	&uevent_helper_attr.attr,
+#endif
+#ifdef CONFIG_KEXEC
+	&kexec_loaded_attr.attr,
+	&kexec_crash_loaded_attr.attr,
 #endif
 	NULL
 };