litmus core: add dump-trace-buffer magic sysrq

Pump stuff from the TRACE() buffer to printk() on demand.

3 files changed, 49 insertions, 3 deletions

diff --git a/include/litmus/sched_trace.h b/include/litmus/sched_trace.h
index 28feee82dc..afd0391d12 100644
--- a/include/litmus/sched_trace.h
+++ b/include/litmus/sched_trace.h
@@ -179,7 +179,7 @@ feather_callback void do_sched_trace_sys_release(unsigned long id,
 
 #ifdef CONFIG_SCHED_DEBUG_TRACE
 void sched_trace_log_message(const char* fmt, ...);
-
+void dump_trace_buffer(int max);
 #else
 
 #define sched_trace_log_message(fmt, ...)
diff --git a/kernel/printk.c b/kernel/printk.c
index 9eb2dc5e27..4423a5542e 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -59,6 +59,7 @@ int console_printk[4] = {
  */
 #include <litmus/litmus.h>
 int trace_override = 0;
+int trace_recurse  = 0;
 
 /*
  * Low level drivers may need that to know if they can schedule in
@@ -658,7 +659,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 
         /* Emit the output into the temporary buffer */
         printed_len = vscnprintf(printk_buf, sizeof(printk_buf), fmt, args);
-        if (trace_override)
+        if (trace_override && !trace_recurse)
                 TRACE("%s", printk_buf);
 
         /*
diff --git a/litmus/sched_trace.c b/litmus/sched_trace.c
index 527a58b696..9ee6f02a61 100644
--- a/litmus/sched_trace.c
+++ b/litmus/sched_trace.c
@@ -9,6 +9,7 @@
 #include <asm/semaphore.h>
 #include <asm/uaccess.h>
 #include <linux/module.h>
+#include <linux/sysrq.h>
 
 #include <litmus/sched_trace.h>
 #include <litmus/litmus.h>
@@ -300,7 +301,10 @@ static ssize_t log_read(struct file *filp, char __user *to, size_t len,
 
 
 
+/* in kernel/printk.c */
 extern int trace_override;
+extern int trace_recurse;
+
 
 /* log_open - open the global log message ring buffer.
  */
@@ -328,7 +332,8 @@ static int log_open(struct inode *in, struct file *filp)
         error = 0;
         filp->private_data = buf;
         printk(KERN_DEBUG "sched_trace buf: from 0x%p to 0x%p  length: %x\n",
-               buf->buf.buf, buf->buf.end, buf->buf.end - buf->buf.buf);
+               buf->buf.buf, buf->buf.end,
+               (unsigned int) (buf->buf.end - buf->buf.buf));
         trace_override++;
  out_unlock:
         up(&buf->reader_mutex);
@@ -415,11 +420,35 @@ static int __init register_buffer_dev(const char* name,
 
 }
 
+#ifdef CONFIG_MAGIC_SYSRQ
+
+static void sysrq_dump_trace_buffer(int key, struct tty_struct *tty)
+{
+        dump_trace_buffer(100);
+}
+
+static struct sysrq_key_op sysrq_dump_trace_buffer_op = {
+        .handler        = sysrq_dump_trace_buffer,
+        .help_msg       = "dump-trace-buffer(Y)",
+        .action_msg     = "writing content of TRACE() buffer",
+};
+
+#endif
+
 static int __init init_sched_trace(void)
 {
         printk("Initializing TRACE() device\n");
         init_log_buffer();
 
+#ifdef CONFIG_MAGIC_SYSRQ
+        /* offer some debugging help */
+        if (!register_sysrq_key('y', &sysrq_dump_trace_buffer_op))
+                printk("Registered dump-trace-buffer(Y) magic sysrq.\n");
+        else
+                printk("Could not register dump-trace-buffer(Y) magic sysrq.\n");
+#endif
+
+
         return register_buffer_dev("litmus_log", &log_fops,
                                    LOG_MAJOR, 1);
 }
@@ -460,3 +489,19 @@ void sched_trace_log_message(const char* fmt, ...)
         local_irq_restore(flags);
         va_end(args);
 }
+
+void dump_trace_buffer(int max)
+{
+        char line[80];
+        int len;
+        int count = 0;
+
+        /* potential but very unlikely race... */
+        trace_recurse = 1;
+        while ((max == 0 || count++ < max) &&
+               (len = rb_get(&log_buffer.buf, line, sizeof(line) - 1)) > 0) {
+                line[len] = '\0';
+                printk("%s", line);
+        }
+        trace_recurse = 0;
+}