Add a cnputs() function to write a string to the console with

a lock to prevent interspersed strings written from different CPUs
at the same time.

To avoid putting a buffer on the stack or having to malloc one,
space is incorporated in the per-cpu structure. The buffer
size if 128 bytes; chosen because it's the next power of 2 size
up from 80 characters.

String writes to the console are buffered up the end of the line
or until the buffer fills. Then the buffer is flushed to all
console devices.

Existing low level console output via cnputc() is unaffected by
this change. ithread calls to log() are also unaffected to avoid
blocking those threads.

A minor change to the behaviour in a panic situation is that
console output will still be buffered, but won't be written to
a tty as before. This should prevent interspersed panic output
as a number of CPUs panic before we end up single threaded
running ddb.

Reviewed by:	scottl, jhb
MFC after:	2 weeks

1 files changed, 72 insertions, 17 deletions

diff --git a/sys/kern/subr_prf.c b/sys/kern/subr_prf.c
index bef5566..b6ffc91 100644
--- a/sys/kern/subr_prf.c
+++ b/sys/kern/subr_prf.c
@@ -78,6 +78,10 @@ struct putchar_arg {
 	int	flags;
 	int	pri;
 	struct	tty *tty;
+	char	*p_bufr;
+	size_t	n_bufr;
+	char	*p_next;
+	size_t	remain;
 };
 
 struct snprintf_arg {
@@ -92,7 +96,6 @@ static void  putchar(int ch, void *arg);
 static char *ksprintn(char *nbuf, uintmax_t num, int base, int *len, int upper);
 static void  snprintf_func(int ch, void *arg);
 
-static int consintr = 1;		/* Ok to handle console interrupts? */
 static int msgbufmapped;		/* Set when safe to use msgbuf */
 int msgbuftrigger;
 
@@ -234,6 +237,7 @@ log(int level, const char *fmt, ...)
 	pca.tty = NULL;
 	pca.pri = level;
 	pca.flags = log_open ? TOLOG : TOCONS;
+	pca.p_bufr = NULL;
 
 	va_start(ap, fmt);
 	kvprintf(fmt, putchar, &pca, 10, ap);
@@ -284,43 +288,96 @@ int
 printf(const char *fmt, ...)
 {
 	va_list ap;
-	int savintr;
 	struct putchar_arg pca;
 	int retval;
 
-	savintr = consintr;		/* disable interrupts */
-	consintr = 0;
+	critical_enter();
+
 	va_start(ap, fmt);
 	pca.tty = NULL;
 	pca.flags = TOCONS | TOLOG;
 	pca.pri = -1;
+	pca.p_bufr = (char *) PCPU_PTR(cons_bufr);
+	pca.p_next = pca.p_bufr;
+	pca.n_bufr = PCPU_CONS_BUFR;
+	pca.remain = PCPU_CONS_BUFR;
+	*pca.p_next = '\0';
+
 	retval = kvprintf(fmt, putchar, &pca, 10, ap);
 	va_end(ap);
+
+	/* Write any buffered console output: */
+	if (*pca.p_bufr != '\0')
+		cnputs(pca.p_bufr);
+
 	if (!panicstr)
 		msgbuftrigger = 1;
-	consintr = savintr;		/* reenable interrupts */
+
+	critical_exit();
+
 	return (retval);
 }
 
 int
 vprintf(const char *fmt, va_list ap)
 {
-	int savintr;
 	struct putchar_arg pca;
 	int retval;
 
-	savintr = consintr;		/* disable interrupts */
-	consintr = 0;
+	critical_enter();
+
 	pca.tty = NULL;
 	pca.flags = TOCONS | TOLOG;
 	pca.pri = -1;
+	pca.p_bufr = (char *) PCPU_PTR(cons_bufr);
+	pca.p_next = pca.p_bufr;
+	pca.n_bufr = PCPU_CONS_BUFR;
+	pca.remain = PCPU_CONS_BUFR;
+	*pca.p_next = '\0';
+
 	retval = kvprintf(fmt, putchar, &pca, 10, ap);
+
+	/* Write any buffered console output: */
+	if (*pca.p_bufr != '\0')
+		cnputs(pca.p_bufr);
+
 	if (!panicstr)
 		msgbuftrigger = 1;
-	consintr = savintr;		/* reenable interrupts */
+
+	critical_exit();
+
 	return (retval);
 }
 
+static void
+putcons(int c, struct putchar_arg *ap)
+{
+	/* Check if no console output buffer was provided. */
+	if (ap->p_bufr == NULL)
+		/* Output direct to the console. */
+		cnputc(c);
+	else {
+		/* Buffer the character: */
+		if (c == '\n') {
+			*ap->p_next++ = '\r';
+			ap->remain--;
+		}
+		*ap->p_next++ = c;
+		ap->remain--;
+
+		/* Always leave the buffer zero terminated. */
+		*ap->p_next = '\0';
+
+		/* Check if the buffer needs to be flushed. */
+		if (ap->remain < 3 || c == '\n') {
+			cnputs(ap->p_bufr);
+			ap->p_next = ap->p_bufr;
+			ap->remain = ap->n_bufr;
+			*ap->p_next = '\0';
+		}
+	}
+}
+
 /*
  * Print a character on console or users terminal.  If destination is
  * the console then the last bunch of characters are saved in msgbuf for
@@ -331,17 +388,15 @@ putchar(int c, void *arg)
 {
 	struct putchar_arg *ap = (struct putchar_arg*) arg;
 	struct tty *tp = ap->tty;
-	int consdirect, flags = ap->flags;
+	int flags = ap->flags;
 
-	consdirect = ((flags & TOCONS) && constty == NULL);
 	/* Don't use the tty code after a panic or while in ddb. */
-	if (panicstr)
-		consdirect = 1;
-	if (kdb_active)
-		consdirect = 1;
-	if (consdirect) {
+	if (kdb_active) {
 		if (c != '\0')
 			cnputc(c);
+	} else if (panicstr || ((flags & TOCONS) && constty == NULL)) {
+		if (c != '\0')
+			putcons(c, ap);
 	} else {
 		if ((flags & TOTTY) && tp != NULL)
 			tputchar(c, tp);
@@ -349,7 +404,7 @@ putchar(int c, void *arg)
 			if (constty != NULL)
 				msgbuf_addchar(&consmsgbuf, c);
 			if (always_console_output && c != '\0')
-				cnputc(c);
+				putcons(c, ap);
 		}
 	}
 	if ((flags & TOLOG))