[RFC PATCH 1/2] random: Expose boot ID to other subsystems

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Add get_boot_id() to expose current boot ID to other kernel subsystems.
Note that since this is only meaningful if user can access it via sysctl,
it returns NULL if CONFIG_SYSCTL=n.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 drivers/char/random.c  |   27 +++++++++++++++++++++------
 include/linux/random.h |    9 +++++++++
 2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index b4da1fb976c1..96a5a165627a 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1615,6 +1615,25 @@ static int sysctl_random_write_wakeup_bits = POOL_READY_BITS;
 static int sysctl_poolsize = POOL_BITS;
 static u8 sysctl_bootid[UUID_SIZE];
 
+/**
+ * get_boot_id - return the boot ID UUID
+ *
+ * This function returns a pointer to the boot ID UUID, which is generated on
+ * demand the first time this function is called. The boot ID is a UUID that
+ * is unique to each boot of the system.
+ */
+const u8 *get_boot_id(void)
+{
+	static DEFINE_SPINLOCK(bootid_spinlock);
+
+	spin_lock(&bootid_spinlock);
+	if (!sysctl_bootid[8])
+		generate_random_uuid(sysctl_bootid);
+	spin_unlock(&bootid_spinlock);
+
+	return sysctl_bootid;
+}
+
 /*
  * This function is used to return both the bootid UUID, and random
  * UUID. The difference is in whether table->data is NULL; if it is,
@@ -1638,12 +1657,8 @@ static int proc_do_uuid(const struct ctl_table *table, int write, void *buf,
 		uuid = tmp_uuid;
 		generate_random_uuid(uuid);
 	} else {
-		static DEFINE_SPINLOCK(bootid_spinlock);
-
-		spin_lock(&bootid_spinlock);
-		if (!uuid[8])
-			generate_random_uuid(uuid);
-		spin_unlock(&bootid_spinlock);
+		/* Ensure that the boot ID is initialized. */
+		get_boot_id();
 	}
 
 	snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
diff --git a/include/linux/random.h b/include/linux/random.h
index 8a8064dc3970..aaf630f14931 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -130,6 +130,15 @@ static inline int get_random_bytes_wait(void *buf, size_t nbytes)
 	return ret;
 }
 
+#ifdef CONFIG_SYSCTL
+const u8 *get_boot_id(void);
+#else
+static inline const u8 *get_boot_id(void)
+{
+	return NULL;
+}
+#endif
+
 #ifdef CONFIG_SMP
 int random_prepare_cpu(unsigned int cpu);
 int random_online_cpu(unsigned int cpu);