dmesg: fix console-level off-by-one

  commit f06ec64f dmesg; support level names (e.g. --console-level=alert)

introduced an off-by-one error.  The kernel will print messages with
a *higher* level than the console-level. The bug made it impossible to
set the level for debugging, like it is documented in e.g
Documentation/networking/netconsole.txt :

 nemi:/tmp# dmesg -n 8
 dmesg: unknown level '8'

And attempting to set the "emerg" level would result in an invalid 0 value:

 nemi:/tmp# dmesg -n emerg
 dmesg: klogctl failed: Invalid argument

Restoring the old behaviour for numeric levels, and mapping the level
names so that "dmesg -n debug" behaves as expected: logging everything
at level "debug" and higher.

[kzak@redhat.com: - add comment to parse_level()]

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 17 insertions, 5 deletions

diff --git a/sys-utils/dmesg.c b/sys-utils/dmesg.c
index 0ee03eeba..4c85f9fce 100644
--- a/sys-utils/dmesg.c
+++ b/sys-utils/dmesg.c
@@ -227,24 +227,36 @@ static void __attribute__((__noreturn__)) usage(FILE *out)
 
 /*
  * LEVEL     ::= <number> | <name>
- *  <number> ::= number in range <0..N>, where N < ARRAY_SIZE(level_names)
+ *  <number> ::= @len is set:  number in range <0..N>, where N < ARRAY_SIZE(level_names)
+ *           ::= @len not set: number in range <1..N>, where N <= ARRAY_SIZE(level_names)
  *  <name>   ::= case-insensitive text
+ *
+ *  Note that @len argument is not set when parsing "-n <level>" command line
+ *  option. The console_level is intepreted as "log level less than the value".
+ *
+ *  For example "dmesg -n 8" or "dmesg -n debug" enables debug console log
+ *  level by klogctl(SYSLOG_ACTION_CONSOLE_LEVEL, NULL, 8). The @str argument
+ *  has to be parsed to number in range <1..8>.
  */
 static int parse_level(const char *str, size_t len)
 {
+	int offset = 0;
+
 	if (!str)
 		return -1;
-	if (!len)
+	if (!len) {
 		len = strlen(str);
+		offset = 1;
+	}
 	errno = 0;
 
 	if (isdigit(*str)) {
 		char *end = NULL;
-		long x = strtol(str, &end, 10);
+		long x = strtol(str, &end, 10) - offset;
 
 		if (!errno && end && end > str && (size_t) (end - str) == len &&
 		    x >= 0 && (size_t) x < ARRAY_SIZE(level_names))
-			return x;
+			return x + offset;
 	} else {
 		size_t i;
 
@@ -252,7 +264,7 @@ static int parse_level(const char *str, size_t len)
 			const char *n = level_names[i].name;
 
 			if (strncasecmp(str, n, len) == 0 && *(n + len) == '\0')
-				return i;
+				return i + offset;
 		}
 	}