linux-kernel - Re: [PATCH] char: Prefer pr

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Date:	Mon, 06 Jun 2016 08:23:29 -0700
From:	Joe Perches <joe@...ches.com>
To:	Greg KH <gregkh@...uxfoundation.org>,
	Jyoti Singh <jssengar92@...il.com>
Cc:	arnd@...db.de, linux-kernel@...r.kernel.org,
	Jyoti Singh <jssengar@...il.com>
Subject: Re: [PATCH] char: Prefer pr_* instead of printk

On Sat, 2016-06-04 at 09:36 -0700, Greg KH wrote:
> On Sat, Jun 04, 2016 at 08:15:11PM +0530, Jyoti Singh wrote:
> > 
> > This patch replaces all the printk[KERN_INFO] with pr_* in the file
> > "ttyprintk.c" addressing the following warning:
> > 
> > WARNING:Prefer [subsystem eg: netdev]_info([subsystem]dev, ...
> > then dev_info(dev,... then pr_info(...  to printk(KERN_INFO ...
> > Found with checkpatch
> Sometimes checkpatch tells you to do things that are incorrect :)
> 
> Are you _sure_ the code works the same before and after this?  The
> ttyprintk driver is a bit "special".

when pr_fmt is not defined (and ttyprint doesn't use pr_fmt),
pr_<level> uses are printks.

#define pr_info(fmt, ...) \
	printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)

The only one that is not a printk is pr_debug.

It'd be simpler code if all the printks in this file were
consolidated into something like a single tpk_flush function
and the tpk_tag removed.

Something like (completely untested, just typed and compiled
with a couple typos fixed)
---
 drivers/char/ttyprintk.c | 69 ++++++++++++++++++++++--------------------------
 1 file changed, 31 insertions(+), 38 deletions(-)

diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
index b098d2d..67549ce 100644
--- a/drivers/char/ttyprintk.c
+++ b/drivers/char/ttyprintk.c
@@ -31,60 +31,53 @@ static struct ttyprintk_port tpk_port;
  * printk messages (also suitable for logging service):
  * - any cr is replaced by nl
  * - adds a ttyprintk source tag in front of each line
- * - too long message is fragmeted, with '\'nl between fragments
- * - TPK_STR_SIZE isn't really the write_room limiting factor, bcause
+ * - too long message is fragmented, with '\'nl between fragments
+ * - TPK_STR_SIZE isn't really the write_room limiting factor, because
  *   it is emptied on the fly during preformatting.
  */
 #define TPK_STR_SIZE 508 /* should be bigger then max expected line length */
 #define TPK_MAX_ROOM 4096 /* we could assume 4K for instance */
-static const char *tpk_tag = "[U] "; /* U for User */
 static int tpk_curr;
 
+static char tpk_buffer[TPK_STR_SIZE + 4];
+
+static void tpk_flush(void)
+{
+	if (tpk_curr > 0) {
+		tpk_buffer[tpk_curr] = '\0';
+		pr_info("[U] %s\n", tpk_buffer);
+		tpk_curr = 0;
+	}
+}
+
 static int tpk_printk(const unsigned char *buf, int count)
 {
-	static char tmp[TPK_STR_SIZE + 4];
 	int i = tpk_curr;
 
 	if (buf == NULL) {
-		/* flush tmp[] */
-		if (tpk_curr > 0) {
-			/* non nl or cr terminated message - add nl */
-			tmp[tpk_curr + 0] = '\n';
-			tmp[tpk_curr + 1] = '\0';
-			printk(KERN_INFO "%s%s", tpk_tag, tmp);
-			tpk_curr = 0;
-		}
+		tpk_flush();
 		return i;
 	}
 
 	for (i = 0; i < count; i++) {
-		tmp[tpk_curr] = buf[i];
-		if (tpk_curr < TPK_STR_SIZE) {
-			switch (buf[i]) {
-			case '\r':
-				/* replace cr with nl */
-				tmp[tpk_curr + 0] = '\n';
-				tmp[tpk_curr + 1] = '\0';
-				printk(KERN_INFO "%s%s", tpk_tag, tmp);
-				tpk_curr = 0;
-				if ((i + 1) < count && buf[i + 1] == '\n')
-					i++;
-				break;
-			case '\n':
-				tmp[tpk_curr + 1] = '\0';
-				printk(KERN_INFO "%s%s", tpk_tag, tmp);
-				tpk_curr = 0;
-				break;
-			default:
-				tpk_curr++;
-			}
-		} else {
+		if (tpk_curr >= TPK_STR_SIZE) {
 			/* end of tmp buffer reached: cut the message in two */
-			tmp[tpk_curr + 1] = '\\';
-			tmp[tpk_curr + 2] = '\n';
-			tmp[tpk_curr + 3] = '\0';
-			printk(KERN_INFO "%s%s", tpk_tag, tmp);
-			tpk_curr = 0;
+			tpk_buffer[tpk_curr++] = '\\';
+			tpk_flush();
+		}
+
+		switch (buf[i]) {
+		case '\r':
+			tpk_flush();
+			if ((i + 1) < count && buf[i + 1] == '\n')
+				i++;
+			break;
+		case '\n':
+			tpk_flush();
+			break;
+		default:
+			tpk_buffer[tpk_curr++] = buf[i];
+			break;
 		}
 	}