[PATCH 1/8] tty: Define ASYNC_ replacement bits

From: Peter Hurley
Date: Sat Apr 09 2016 - 20:55:47 EST


Prepare for relocating kernel private state bits out of tty_port::flags
field; tty_port::flags field is not atomic and can become corrupted
by concurrent updates. It also suffers from the complication of sharing
in a userspace-visible field which must be masked.

Define new tty_port::iflags field and new, substitute bit definitions
for the former ASYNC_* flags.

Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
include/linux/tty.h | 16 +++++++++++++++-
include/uapi/linux/tty_flags.h | 9 ++++++++-
2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 89f9c91..4e0dbda0 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -228,7 +228,8 @@ struct tty_port {
int count; /* Usage count */
wait_queue_head_t open_wait; /* Open waiters */
wait_queue_head_t delta_msr_wait; /* Modem status change */
- unsigned long flags; /* TTY flags ASY_*/
+ unsigned long flags; /* User TTY flags ASYNC_ */
+ unsigned long iflags; /* Internal flags TTY_PORT_ */
unsigned char console:1, /* port is a console */
low_latency:1; /* optional: tune for latency */
struct mutex mutex; /* Locking */
@@ -242,6 +243,19 @@ struct tty_port {
struct kref kref; /* Ref counter */
};

+/* tty_port::iflags bits -- use atomic bit ops */
+#define TTY_PORT_INITIALIZED 0 /* device is initialized */
+#define TTY_PORT_SUSPENDED 1 /* device is suspended */
+#define TTY_PORT_ACTIVE 2 /* device is open */
+
+/*
+ * uart drivers: use the uart_port::status field and the UPSTAT_* defines
+ * for s/w-based flow control steering and carrier detection status
+ */
+#define TTY_PORT_CTS_FLOW 3 /* h/w flow control enabled */
+#define TTY_PORT_CHECK_CD 4 /* carrier detect enabled */
+
+
/*
* Where all of the state associated with a tty is kept while the tty
* is open. Since the termios state should be kept even if the tty
diff --git a/include/uapi/linux/tty_flags.h b/include/uapi/linux/tty_flags.h
index 072e41e..8e1a436 100644
--- a/include/uapi/linux/tty_flags.h
+++ b/include/uapi/linux/tty_flags.h
@@ -32,7 +32,12 @@
#define ASYNCB_MAGIC_MULTIPLIER 16 /* Use special CLK or divisor */
#define ASYNCB_LAST_USER 16

-/* Internal flags used only by kernel */
+/*
+ * Internal flags used only by kernel (read-only)
+ *
+ * WARNING: These flags are no longer used and have been superceded by the
+ * TTY_PORT_ flags in the iflags field (and not userspace-visible)
+ */
#define ASYNCB_INITIALIZED 31 /* Serial port was initialized */
#define ASYNCB_SUSPENDED 30 /* Serial port is suspended */
#define ASYNCB_NORMAL_ACTIVE 29 /* Normal device is active */
@@ -44,6 +49,7 @@
#define ASYNCB_CONS_FLOW 23 /* flow control for console */
#define ASYNCB_FIRST_KERNEL 22

+/* Masks */
#define ASYNC_HUP_NOTIFY (1U << ASYNCB_HUP_NOTIFY)
#define ASYNC_SUSPENDED (1U << ASYNCB_SUSPENDED)
#define ASYNC_FOURPORT (1U << ASYNCB_FOURPORT)
@@ -72,6 +78,7 @@
#define ASYNC_SPD_WARP (ASYNC_SPD_HI|ASYNC_SPD_SHI)
#define ASYNC_SPD_MASK (ASYNC_SPD_HI|ASYNC_SPD_VHI|ASYNC_SPD_SHI)

+/* These flags are no longer used (and were always masked from userspace) */
#define ASYNC_INITIALIZED (1U << ASYNCB_INITIALIZED)
#define ASYNC_NORMAL_ACTIVE (1U << ASYNCB_NORMAL_ACTIVE)
#define ASYNC_BOOT_AUTOCONF (1U << ASYNCB_BOOT_AUTOCONF)
--
2.8.1