[src/trunk]: src/sys/dev cons(9): New function cn_set_tab.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/f2e6d45c5a12
branches:  trunk
changeset: 371715:f2e6d45c5a12
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Oct 03 19:12:29 2022 +0000

description:
cons(9): New function cn_set_tab.

Increment of progress toward eliminating bare access to cn_tab so we
can make more things MP-safe without the kernel lock (and maybe some
day better formalize console detection and switching).

diffstat:

 sys/dev/cons.c |  20 ++++++++++++++++++--
 sys/dev/cons.h |   4 +++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diffs (59 lines):

diff -r 02e77497e6d1 -r f2e6d45c5a12 sys/dev/cons.c
--- a/sys/dev/cons.c    Mon Oct 03 17:42:35 2022 +0000
+++ b/sys/dev/cons.c    Mon Oct 03 19:12:29 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cons.c,v 1.79 2022/08/22 00:20:56 riastradh Exp $      */
+/*     $NetBSD: cons.c,v 1.80 2022/10/03 19:12:29 riastradh Exp $      */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -39,7 +39,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: cons.c,v 1.79 2022/08/22 00:20:56 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: cons.c,v 1.80 2022/10/03 19:12:29 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/proc.h>
@@ -87,6 +87,22 @@
 struct consdev *cn_tab;        /* physical console device info */
 struct vnode *cn_devvp[2];     /* vnode for underlying device. */
 
+void
+cn_set_tab(struct consdev *tab)
+{
+
+       /*
+        * This is a point that we should have KASSERT(cold) or add
+        * synchronization in case this can happen after cold boot.
+        * However, cn_tab initialization is so critical to any
+        * diagnostics or debugging that we need to tread carefully
+        * about introducing new ways to crash.  So let's put the
+        * assertion in only after we've audited most or all of the
+        * cn_tab updates.
+        */
+       cn_tab = tab;
+}
+
 int
 cnopen(dev_t dev, int flag, int mode, struct lwp *l)
 {
diff -r 02e77497e6d1 -r f2e6d45c5a12 sys/dev/cons.h
--- a/sys/dev/cons.h    Mon Oct 03 17:42:35 2022 +0000
+++ b/sys/dev/cons.h    Mon Oct 03 19:12:29 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cons.h,v 1.28 2022/08/28 09:52:43 riastradh Exp $      */
+/*     $NetBSD: cons.h,v 1.29 2022/10/03 19:12:29 riastradh Exp $      */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -76,6 +76,8 @@
 extern struct consdev constab[];
 extern struct consdev *cn_tab;
 
+void   cn_set_tab(struct consdev *);
+
 void   cninit(void);
 int    cngetc(void);
 int    cngetsn(char *, int);