Add --enable-debug-log configure option

Until now the notion of an internal debug logging infrastructure
was conflated with enabling ASSERT()s.  This patch clarifies things
by cleanly breaking the two subsystem apart.  The result of this
is the following behavior.

--enable-debug      - Enable/disable code wrapped in ASSERT()s.
--disable-debug       ASSERT()s are used to check invariants and
                      are never required for correct operation.
                      They are disabled by default because they
                      may impact performance.

--enable-debug-log  - Enable/disable the debug log infrastructure.
--disable-debug-log   This infrastructure allows the spl code and
                      its consumer to log messages to an in-kernel
                      log.  The granularity of the logging can be
                      controlled by a debug mask.  By default the
                      mask disables most debug messages resulting
                      in a negligible performance impact.  Because
                      of this the debug log is enabled by default.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/spl/spl-debug.c

@@ -47,6 +47,9 @@
 
 #define SS_DEBUG_SUBSYS SS_DEBUG
 
+/* Debug log support enabled */
+#ifdef DEBUG_LOG
+
 unsigned long spl_debug_subsys = ~0;
 EXPORT_SYMBOL(spl_debug_subsys);
 module_param(spl_debug_subsys, ulong, 0644);
@@ -1248,3 +1251,5 @@ spl_debug_fini(void)
 {
         trace_fini();
 }
+
+#endif /* DEBUG_LOG */

module/spl/spl-err.c

@@ -34,7 +34,7 @@
 
 #define SS_DEBUG_SUBSYS SS_GENERIC
 
-#ifndef NDEBUG
+#ifdef DEBUG_LOG
 static char ce_prefix[CE_IGNORE][10] = { "", "NOTICE: ", "WARNING: ", "" };
 static char ce_suffix[CE_IGNORE][2] = { "", "\n", "\n", "" };
 #endif

module/spl/spl-kmem.c

@@ -672,7 +672,7 @@ kmem_alloc_debug(size_t size, int flags, const char *func, int line,
 		    "large kmem_alloc(%llu, 0x%x) at %s:%d (%lld/%llu)\n",
 		    (unsigned long long) size, flags, func, line,
 		    kmem_alloc_used_read(), kmem_alloc_max);
-		spl_debug_dumpstack(NULL);
+		dump_stack();
 	}
 
 	/* Use the correct allocator */

module/spl/spl-proc.c

@@ -125,6 +125,7 @@ enum {
 	CTL_HW_SERIAL,			/* Hardware serial number from hostid */
 	CTL_KALLSYMS,			/* Address of kallsyms_lookup_name */
 
+#ifdef DEBUG_LOG
 	CTL_DEBUG_SUBSYS,		/* Debug subsystem */
 	CTL_DEBUG_MASK,			/* Debug mask */
 	CTL_DEBUG_PRINTK,		/* Force all messages to console */
@@ -136,6 +137,7 @@ enum {
 	CTL_DEBUG_DUMP,			/* Dump debug buffer to file */
 	CTL_DEBUG_FORCE_BUG,		/* Hook to force a BUG */
 	CTL_DEBUG_STACK_SIZE,		/* Max observed stack size */
+#endif
 
 	CTL_CONSOLE_RATELIMIT,		/* Ratelimit console messages */
 	CTL_CONSOLE_MAX_DELAY_CS,	/* Max delay which we skip messages */
@@ -221,6 +223,7 @@ proc_copyout_string(char *ubuffer, int ubuffer_size,
         return size;
 }
 
+#ifdef DEBUG_LOG
 SPL_PROC_HANDLER(proc_dobitmasks)
 {
         unsigned long *mask = table->data;
@@ -407,6 +410,7 @@ SPL_PROC_HANDLER(proc_console_backoff)
 
         SRETURN(rc);
 }
+#endif /* DEBUG_LOG */
 
 #ifdef DEBUG_KMEM
 SPL_PROC_HANDLER(proc_domemused)
@@ -716,6 +720,7 @@ static struct file_operations proc_slab_operations = {
 };
 #endif /* DEBUG_KMEM */
 
+#ifdef DEBUG_LOG
 static struct ctl_table spl_debug_table[] = {
         {
                 CTL_NAME    (CTL_DEBUG_SUBSYS)
@@ -829,6 +834,7 @@ static struct ctl_table spl_debug_table[] = {
         },
 	{0},
 };
+#endif /* DEBUG_LOG */
 
 static struct ctl_table spl_vm_table[] = {
         {
@@ -1056,12 +1062,14 @@ static struct ctl_table spl_table[] = {
                 .proc_handler = &proc_dokallsyms_lookup_name,
         },
 #endif
+#ifdef DEBUG_LOG
 	{
 		CTL_NAME    (CTL_SPL_DEBUG)
 		.procname = "debug",
 		.mode     = 0555,
 		.child    = spl_debug_table,
 	},
+#endif
 	{
 		CTL_NAME    (CTL_SPL_VM)
 		.procname = "vm",