utils: Don't lose log level when silencing kmsg

Once we disable kmsg logging to the console, the kernel will set the
console log level to the minimum log level (i.e. only logging kernel
panics). However the unintended side effect is that our own kmsg-reader
will start filtering out all kernel log messages, since we also respect
the kernel's console log level.

This change make it so that we keep using the original console log level
whenever we disable the kernel's output. This lets us keep forwarding
the kernel's kmsg output

diff --git a/src/libply/ply-utils.c b/src/libply/ply-utils.c
index 6fa649755a2d5edfe8daac7192409148d759d071..782fadd87a4aedc91bcee1bcb8856fb0209aaf4a 100644 (file)
--- a/src/libply/ply-utils.c
+++ b/src/libply/ply-utils.c
@@ -89,6 +89,10 @@ static int overridden_device_scale = 0;
 static char kernel_command_line[PLY_MAX_COMMAND_LINE_SIZE];
 static bool kernel_command_line_is_set;
 
+static int cached_current_log_level = 0;
+static int cached_default_log_level = 0;
+static double log_level_update_time = 0.0;
+
 bool
 ply_open_unidirectional_pipe (int *sender_fd,
                               int *receiver_fd)
@@ -673,20 +677,6 @@ ply_create_file_link (const char *source,
         return true;
 }
 
-void
-ply_show_new_kernel_messages (bool should_show)
-{
-        int type;
-
-        if (should_show)
-                type = PLY_ENABLE_CONSOLE_PRINTK;
-        else
-                type = PLY_DISABLE_CONSOLE_PRINTK;
-
-        if (klogctl (type, NULL, 0) < 0)
-                ply_trace ("could not toggle printk visibility: %m");
-}
-
 ply_daemon_handle_t *
 ply_create_daemon (void)
 {
@@ -1118,26 +1108,14 @@ int ply_guess_device_scale (uint32_t width,
         return get_device_scale (width, height, 0, 0, true);
 }
 
-void
-ply_get_kmsg_log_levels (int *current_log_level,
-                         int *default_log_level)
+static void
+ply_get_kmsg_log_levels_uncached (int *current_log_level,
+                                  int *default_log_level)
 {
-        static double last_update_time = 0;
-        static int cached_current_log_level = 0;
-        static int cached_default_log_level = 0;
         char log_levels[4096] = "";
-        double current_time;
         char *field, *fields;
         int fd;
 
-        current_time = ply_get_timestamp ();
-
-        if ((current_time - last_update_time) < 1.0) {
-                *current_log_level = cached_current_log_level;
-                *default_log_level = cached_default_log_level;
-                return;
-        }
-
         ply_trace ("opening /proc/sys/kernel/printk");
         fd = open ("/proc/sys/kernel/printk", O_RDONLY);
 
@@ -1171,11 +1149,48 @@ ply_get_kmsg_log_levels (int *current_log_level,
         }
 
         *default_log_level = atoi (field);
+}
 
-        cached_current_log_level = *current_log_level;
-        cached_default_log_level = *default_log_level;
+void
+ply_get_kmsg_log_levels (int *current_log_level,
+                         int *default_log_level)
+{
+        double current_time;
+        bool no_cache;
+        bool cache_expired;
+
+        no_cache = cached_current_log_level == 0 || cached_default_log_level == 0;
+        current_time = ply_get_timestamp ();
+        cache_expired = log_level_update_time > 0.0 && (current_time - log_level_update_time) >= 1.0;
+
+        if (no_cache || cache_expired) {
+                ply_get_kmsg_log_levels_uncached (&cached_current_log_level, &cached_default_log_level);
+                log_level_update_time = current_time;
+        }
+
+        *current_log_level = cached_current_log_level;
+        *default_log_level = cached_default_log_level;
+}
+
+void
+ply_show_new_kernel_messages (bool should_show)
+{
+        int type;
+
+        if (should_show) {
+                type = PLY_ENABLE_CONSOLE_PRINTK;
+
+                cached_current_log_level = cached_default_log_level = 0;
+                log_level_update_time = 0.0;
+        } else {
+                type = PLY_DISABLE_CONSOLE_PRINTK;
+
+                ply_get_kmsg_log_levels_uncached (&cached_current_log_level, &cached_default_log_level);
+                log_level_update_time = -1.0; /* Disable expiration */
+        }
 
-        last_update_time = current_time;
+        if (klogctl (type, NULL, 0) < 0)
+                ply_trace ("could not toggle printk visibility: %m");
 }
 
 static const char *