linux-kernel - [PATCH] tty: Reserve ldisc 29 for development purposes

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Message-Id: <20220211141036.6403-1-max@enpas.org>
Date:   Fri, 11 Feb 2022 15:10:36 +0100
From:   Max Staudt <max@...as.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Max Staudt <max@...as.org>
Subject: [PATCH] tty: Reserve ldisc 29 for development purposes

It's handy to have an ldisc number free for out-of-tree testing. This
way, a new ldisc can be developed on any running system, without having
to recompile the kernel just to define a new number.

This is the highest number (and also the last one) available under the
old numbering scheme, so let's reserve it before it's too late.

>From now on, every new ldisc upstreamed will have to increment NR_LDISCS
in lockstep with its addition to the table in tty.h.

Signed-off-by: Max Staudt <max@...as.org>
---
 include/uapi/linux/tty.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/tty.h b/include/uapi/linux/tty.h
index a58deb3061eb..9d0f06bfbac3 100644
--- a/include/uapi/linux/tty.h
+++ b/include/uapi/linux/tty.h
@@ -6,8 +6,6 @@
  * 'tty.h' defines some structures used by tty_io.c and some defines.
  */
 
-#define NR_LDISCS		30
-
 /* line disciplines */
 #define N_TTY		0
 #define N_SLIP		1
@@ -39,5 +37,9 @@
 #define N_SPEAKUP	26	/* Speakup communication with synths */
 #define N_NULL		27	/* Null ldisc used for error handling */
 #define N_MCTP		28	/* MCTP-over-serial */
+#define N_DEVELOPMENT	29	/* Manual out-of-tree testing */
+
+/* Always the newest line discipline + 1 */
+#define NR_LDISCS	30
 
 #endif /* _UAPI_LINUX_TTY_H */
-- 
2.30.2