[PATCH printk v2 2/6] console: Introduce unsafe flush policy flags

[John Ogness]

Prepare for per-console atomic flushing policies by introducing a
new nbcon-specific console field @unsafe_flush_flags to store the
unsafe flush policies for a console. The policies are represented
by bits, specified by enum nbcon_unsafe_flush_flags.

Currently it is expected that any @unsafe_flush_flags bits are set
prior to console registration and do not change while registered.

No functional change.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
---
 include/linux/console.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/linux/console.h b/include/linux/console.h
index 06d01f1743512..beb1ee04535b7 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -194,6 +194,29 @@ enum cons_flags {
 	CON_NBCON_ATOMIC_UNSAFE	= BIT(9),
 };
 
+/**
+ * enum nbcon_unsafe_flush_flags - Unsafe atomic flush policy flags
+ * @NBCON_PANIC_FLUSH:		In panic, unsafe flush before kexec or reboot.
+ * @NBCON_PANIC_PRINTK:		In panic, unsafe flush on each printk().
+ * @NBCON_NORMAL_NOTHREAD:	During normal operation, when printing
+ *				kthreads are unreliable or have been shutdown,
+ *				unsafe flush on each printk() or on explicit
+ *				flushing.
+ * @NBCON_KDB:			Unsafe flush kdb output.
+ *
+ * NBCON unsafe atomic flushing always occurs at the end of panic() before
+ * the kernel enters an infinite loop. Users may choose to perform unsafe
+ * flushing in additional scenarios where the current kernel is ending in
+ * order to increase the chances of seeing console messages, even if it is
+ * not safe to do so.
+ */
+enum nbcon_unsafe_flush_flags {
+	NBCON_PANIC_FLUSH	= BIT(0),
+	NBCON_PANIC_PRINTK	= BIT(1),
+	NBCON_NORMAL_NOTHREAD	= BIT(2),
+	NBCON_KDB		= BIT(3),
+};
+
 /**
  * struct nbcon_state - console state for nbcon consoles
  * @atom:	Compound of the state fields for atomic operations
@@ -326,6 +349,7 @@ struct nbcon_write_context {
  * @data:		Driver private data
  * @node:		hlist node for the console list
  *
+ * @unsafe_flush_flags:	Unsafe atomic flush policy. See enum nbcon_unsafe_flush_flags
  * @nbcon_state:	State for nbcon consoles
  * @nbcon_seq:		Sequence number of the next record for nbcon to print
  * @nbcon_device_ctxt:	Context available for non-printing operations
@@ -461,6 +485,8 @@ struct console {
 	 */
 	void (*device_unlock)(struct console *con, unsigned long flags);
 
+	unsigned int		unsafe_flush_flags;
+
 	atomic_t		__private nbcon_state;
 	atomic_long_t		__private nbcon_seq;
 	struct nbcon_context	__private nbcon_device_ctxt;
-- 
2.47.3