[PATCH] commands: dmesg: clear logbuffer fully if not requested otherwise

[Jonas Rebmann <jre@pengutronix.de>]

Previously, `dmesg -c` would clear the logbuffer except for the last 10
lines. This comes with a fair amount of surprise given linux `dmesg -c`
clears the whole logbuffer.

Clear the complete logbuffer given `dmesg -c` but with an optional
argument `dmesg -c [<num>]` to keep <num> lines.

While at it, move the deleteion of log lines to the log_print function
to prevent a corner case of lost log message if they arrive between the
log_print() and log_clean() in dmesg.

If loglevels are selected using -l or -p in addition to cleaning being
selected using -c, only clean those messages shown by the loglevel
selection.

Signed-off-by: Jonas Rebmann <jre@pengutronix.de>
---
 commands/dmesg.c        | 17 ++++++++++-------
 common/console_common.c | 20 +++++++++++++++++---
 include/linux/printk.h  |  2 +-
 3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/commands/dmesg.c b/commands/dmesg.c
index a93ad5b359..6853f3afc9 100644
--- a/commands/dmesg.c
+++ b/commands/dmesg.c
@@ -77,14 +77,20 @@ static unsigned dmesg_get_levels(const char *__args)
 static int do_dmesg(int argc, char *argv[])
 {
 	int opt, ret, i;
-	int delete_buf = 0, emit = 0;
+	int delete_buf = -1, emit = 0;
 	unsigned flags = 0, levels = 0;
 	char *set = NULL;
 
-	while ((opt = getopt(argc, argv, "ctderl:p:n:")) > 0) {
+	while ((opt = getopt(argc, argv, "c::tderl:p:n:")) > 0) {
 		switch (opt) {
 		case 'c':
-			delete_buf = 1;
+			if (optarg) {
+				ret = kstrtoint(optarg, 10, &delete_buf);
+				if (ret || delete_buf < 0)
+					return COMMAND_ERROR_USAGE;
+			} else {
+				delete_buf = 0;
+			}
 			break;
 		case 't':
 			flags |= BAREBOX_LOG_PRINT_TIME;
@@ -155,13 +161,10 @@ static int do_dmesg(int argc, char *argv[])
 		return 0;
 	}
 
-	ret = log_print(flags, levels);
+	ret = log_print(flags, levels, delete_buf);
 	if (ret)
 		return 1;
 
-	if (delete_buf)
-		log_clean(10);
-
 	return 0;
 }
 
diff --git a/common/console_common.c b/common/console_common.c
index 5b7a64c99c..23646d8f81 100644
--- a/common/console_common.c
+++ b/common/console_common.c
@@ -210,12 +210,23 @@ int log_writefile(const char *filepath)
 	return ret < 0 ? ret : nbytes;
 }
 
-int log_print(unsigned flags, unsigned levels)
+/**
+ * log_print - print and optionally clear the log buffer
+ *
+ * @flags:	Flags selecting output formatting
+ * @levels:	bitmask of loglevels to print, 0 for all
+ * @delete_buf:	Number of printed lines to keep in the buffer,
+ *		-1 to keep all.
+ *
+ * This function deletes all messages in the logbuf exceeding
+ * the limit.
+ */
+int log_print(unsigned flags, unsigned levels, int delete_buf)
 {
-	struct log_entry *log;
+	struct log_entry *log, *tmp;
 	unsigned long last = 0;
 
-	list_for_each_entry(log, &barebox_logbuf, list) {
+	list_for_each_entry_safe(log, tmp, &barebox_logbuf, list) {
 		uint64_t time_ns = log->timestamp;
 		unsigned long time;
 
@@ -250,6 +261,9 @@ int log_print(unsigned flags, unsigned levels)
 			printf("] ");
 
 		printf("%s", log->msg);
+
+		if (delete_buf >= 0 && barebox_logbuf_num_messages > delete_buf)
+			log_del(log);
 	}
 
 	return 0;
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 0d7180f0eb..78ab3e6d16 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -192,7 +192,7 @@ extern void log_clean(unsigned int limit);
 #define BAREBOX_LOG_PRINT_TIME		BIT(0)
 
 int log_writefile(const char *filepath);
-int log_print(unsigned flags, unsigned levels);
+int log_print(unsigned flags, unsigned levels, int delete_buf);
 
 struct va_format {
 	const char *fmt;

---
base-commit: 8defba1d0ab1aef9dd5d57710e18d0d02e2c48e2
change-id: 20251017-dmesg-05b9e462e8a1

Best regards,
--  
Jonas Rebmann <jre@pengutronix.de>