syslog() will now automatically redirect output to lowsyslog() if called from an interrupt handler

libc/syslog/lib_lowsyslog.c

@@ -47,6 +47,15 @@
 #include "syslog/syslog.h"
 
 #if defined(CONFIG_ARCH_LOWPUTC) || defined(CONFIG_SYSLOG)
+/* The low-level SYSLOG functions can be used only if we have access to
+ * either the low-level serial interface, up_putc(), and to syslog_putc()
+ */
+
+#if defined(CONFIG_BUILD_FLAT) || defined (__KERNEL__)
+/* The low-level serial interface, up_putc(), and syslog_putc() are only
+ * available in the FLAT build or during the kernel pass of the protected or
+ * kernel two pass builds.
+ */
 
 /****************************************************************************
  * Private Functions
@@ -136,4 +145,5 @@ int lowsyslog(int priority, FAR const IPTR char *fmt, ...)
   return ret;
 }
 
+#endif /* CONFIG_BUILD_FLAT) || __KERNEL__ */
 #endif /* CONFIG_ARCH_LOWPUTC || CONFIG_SYSLOG */

libc/syslog/lib_syslog.c

@@ -43,6 +43,7 @@
 #include <syslog.h>
 
 #include <nuttx/init.h>
+#include <nuttx/arch.h>
 #include <nuttx/clock.h>
 #include <nuttx/streams.h>
 
@@ -162,13 +163,41 @@ int vsyslog(int priority, FAR const IPTR char *fmt, va_list ap)
 {
   int ret = 0;
 
-  /* Check if this priority is enabled */
+#if !defined(CONFIG_SYSLOG) && CONFIG_NFILE_DESCRIPTORS > 0
+  /* Are we are generating output on stdout?  If so, was this function
+   * called from an interrupt handler?  We cannot send data to stdout from
+   * an interrupt handler.
+   */
 
-  if ((g_syslog_mask & LOG_MASK(priority)) != 0)
+  if (up_interrupt_context())
     {
-      /* Yes.. let vsylog_internal do the deed */
+#ifdef CONFIG_ARCH_LOWPUTC
+      /* But the low-level serial interface up_putc() is provided so we may
+       * be able to generate low-level serial output instead.
+       * NOTE: The low-level serial output is not necessarily the same
+       * output destination as stdout!
+       */
 
-      ret = vsyslog_internal(fmt, ap);
+#if defined(CONFIG_BUILD_FLAT) || defined (__KERNEL__)
+      /* lowvsyslog() in only available in the FLAT build or during the
+       * kernel pass of the protected or kernel two pass builds.
+       */
+
+      ret = lowvsyslog(priority, fmt, ap);
+#endif
+#endif
+    }
+  else
+#endif
+    {
+      /* Check if this priority is enabled */
+
+      if ((g_syslog_mask & LOG_MASK(priority)) != 0)
+        {
+          /* Yes.. let vsylog_internal do the deed */
+
+          ret = vsyslog_internal(fmt, ap);
+        }
     }
 
   return ret;