Add /sys/kernel/notes

This patch adds the /sys/kernel/notes magic file.  Reading this delivers the
contents of the kernel's .notes section.  This lets userland easily glean any
detailed information about the running kernel's build that was stored there at
compile time.

Signed-off-by: Roland McGrath <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/ksysfs.c

@@ -62,6 +62,28 @@ static ssize_t kexec_crash_loaded_show(struct kset *kset, char *page)
 KERNEL_ATTR_RO(kexec_crash_loaded);
 #endif /* CONFIG_KEXEC */
 
+/*
+ * Make /sys/kernel/notes give the raw contents of our kernel .notes section.
+ */
+extern const char __start_notes __attribute__((weak));
+extern const char __stop_notes __attribute__((weak));
+#define	notes_size (&__stop_notes - &__start_notes)
+
+static ssize_t notes_read(struct kobject *kobj, struct bin_attribute *bin_attr,
+			  char *buf, loff_t off, size_t count)
+{
+	memcpy(buf, &__start_notes + off, count);
+	return count;
+}
+
+static struct bin_attribute notes_attr = {
+	.attr = {
+		.name = "notes",
+		.mode = S_IRUGO,
+	},
+	.read = &notes_read,
+};
+
 decl_subsys(kernel, NULL, NULL);
 EXPORT_SYMBOL_GPL(kernel_subsys);
 
@@ -88,6 +110,12 @@ static int __init ksysfs_init(void)
 		error = sysfs_create_group(&kernel_subsys.kobj,
 					   &kernel_attr_group);
 
+	if (!error && notes_size > 0) {
+		notes_attr.size = notes_size;
+		error = sysfs_create_bin_file(&kernel_subsys.kobj,
+					      &notes_attr);
+	}
+
 	return error;
 }