[PATCH] kernel/printk.c lockless access

[Linas Vepstas <linas@austin.ibm.com>]

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Hi Linus, Andrew,

I was wondering if you could see your way to accepting the attached
patch, which provides access to the syslog buffer pointers.

The basic idea is that if a system has crashed, it can be handy to
be able to view the contents of the syslog buffer.  Unfortunately,
this is currently hard to do.

 --  char __log_buf[] is declared static in printk.c, so it cannot
     be found in the ksyms table.

 -- do_syslog() uses spinlocks to protect the data structure, and
    so will typically deadlock if called.

The 'fix' is to provide a routine that simply returns the pointers
to the log buffer.  

I'd be thrilled to have this patch accepted ... 

--linas

Signed-off-by: Linas Vepstas <linas@linas.org>



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===== kernel/printk.c 1.47 vs edited =====
--- 1.47/kernel/printk.c	2004-11-19 01:03:10 -06:00
+++ edited/kernel/printk.c	2005-01-06 13:44:36 -06:00
@@ -380,6 +380,23 @@ asmlinkage long sys_syslog(int type, cha
 	return do_syslog(type, buf, len);
 }
 
+#ifdef   CONFIG_DEBUG_KERNEL
+/**
+ * Its very handy to be able to view the syslog buffer during debug.
+ * But do_syslog() uses locks and so it will deadlock if called during 
+ * a debugging session. The routine provides the start and end of the 
+ * physical and logical logs, and is equivalent to do_syslog(3).
+ */
+
+void debugger_syslog_data(char *syslog_data[4])
+{
+	syslog_data[0] = log_buf;
+	syslog_data[1] = log_buf + __LOG_BUF_LEN;
+	syslog_data[2] = log_buf + log_end - (logged_chars < __LOG_BUF_LEN ? logged_chars : __LOG_BUF_LEN);
+	syslog_data[3] = log_buf + log_end;
+}
+#endif   /* CONFIG_DEBUG_KERNEL */
+
 /*
  * Call the console drivers on a range of log_buf
  */