kernel: syslog: Handle userspace kmsg logging

- Add USER_KMSG option to configure if kernel messages
  should be logged in user contexts

- Add syslog_silence() to silence kernel messages in user
  contexts if USER_KMSG is "yes"

Signed-off-by: Ian Moffett <ian@osmora.org>

5 files changed, 35 insertions, 0 deletions

diff --git a/sys/arch/aarch64/conf/GENERIC b/sys/arch/aarch64/conf/GENERIC
index 3271cb7..a716ac2 100644
--- a/sys/arch/aarch64/conf/GENERIC
+++ b/sys/arch/aarch64/conf/GENERIC
@@ -1,5 +1,6 @@
 // Kernel options
 option SERIAL_DEBUG yes     // Enable kmsg serial logging
+option USER_KMSG    yes     // Show kmsg in user consoles
 
 // Kernel constants
 setval SCHED_NQUEUE 4       // Number of scheduler queues (for MLFQ)
diff --git a/sys/arch/amd64/conf/GENERIC b/sys/arch/amd64/conf/GENERIC
index 8e97d6e..7a28038 100644
--- a/sys/arch/amd64/conf/GENERIC
+++ b/sys/arch/amd64/conf/GENERIC
@@ -7,6 +7,7 @@
 //
 option SPECTRE_IBRS no   // Enable the IBRS CPU feature
 option SERIAL_DEBUG yes  // Enable kmsg serial logging
+option USER_KMSG    no   // Show kmsg in user consoles
 
 // Kernel constants
 setval SCHED_NQUEUE 4    // Number of scheduler queues (for MLFQ)
diff --git a/sys/include/sys/syslog.h b/sys/include/sys/syslog.h
index defb341..b9d34ab 100644
--- a/sys/include/sys/syslog.h
+++ b/sys/include/sys/syslog.h
@@ -31,11 +31,13 @@
 #define _SYS_SYSLOG_H_
 
 #include <stdarg.h>
+#include <stdbool.h>
 
 #if defined(_KERNEL)
 
 #define OMIT_TIMESTAMP "\x01"
 
+void syslog_silence(bool option);
 void kprintf(const char *fmt, ...);
 void serial_init(void);
 void serial_putc(char c);
diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index 76fa6fd..665bade 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -130,6 +130,8 @@ main(void)
     begin_install();
 #endif
 
+    syslog_silence(true);
+
     /* Bootstrap APs and here we go! */
     mp_bootstrap_aps(&g_bsp_ci);
     sched_enter();
diff --git a/sys/kern/kern_syslog.c b/sys/kern/kern_syslog.c
index 656362e..db50a3c 100644
--- a/sys/kern/kern_syslog.c
+++ b/sys/kern/kern_syslog.c
@@ -40,8 +40,15 @@
 #define SERIAL_DEBUG 0
 #endif
 
+#if defined(__USER_KMSG)
+#define USER_KMSG __USER_KMSG
+#else
+#define USER_KMSG 0
+#endif
+
 /* Global logger lock */
 static struct spinlock lock = {0};
+static bool no_cons_log = false;
 
 static void
 syslog_write(const char *s, size_t len)
@@ -58,6 +65,15 @@ syslog_write(const char *s, size_t len)
         }
     }
 
+    /*
+     * If the USER_KMSG option is disabled in kconf,
+     * do not log to the console if everything else
+     * has already started.
+     */
+    if (!USER_KMSG && no_cons_log) {
+        return;
+    }
+
     cons_putstr(&g_root_scr, s, len);
 }
 
@@ -116,3 +132,16 @@ kprintf(const char *fmt, ...)
     va_end(ap);
     spinlock_release(&lock);
 }
+
+/*
+ * Silence kernel messages in if the system
+ * is already operating in a user context.
+ *
+ * XXX: This is ignored if the kconf USER_KMSG
+ *      option is set to "no"
+ */
+void
+syslog_silence(bool option)
+{
+    no_cons_log = option;
+}