[PATCH] kernel/printk.c lockless access

Linas Vepstas
2005-01-06T20:03:24Z

[-- Attachment #1: Type: text/plain, Size: 722 bytes --]

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>

[-- Attachment #2: printk.patch --]
[-- Type: text/plain, Size: 940 bytes --]

===== 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
*/