Re: log-buf-len dynamic

[Andrea Arcangeli <andrea@suse.de>]

On Tue, Sep 23, 2003 at 12:40:06PM -0500, Tom Zanussi wrote:
> It may be a little over the top for 2.4, but I posted a patch for a 
> dynamically resizable printk a while back:
> 
> http://marc.theaimsgroup.com/?l=linux-kernel&m=105828314919697&w=2
> 
> I depends on relayfs, which I also posted at the same time.

I don't think we can merge this in 2.4 but it looks good for 2.6.
However note you can't close the overflow issue, you must still have an
high limit, but you can make lots more reliable that way, it's similar
to netlink anyways, that uses dynamic skb to avoid wasting ram. But it's too
invasive for 2.4, just to make a comparison look what my patch looks
like (it will get a bit more complicated because of the request not to
waste the 64k, you know we throw some hundred megs in the per-cpu
freelists so nobody could notice the 64k lost in the 16-way..):

diff -urNp --exclude CVS --exclude BitKeeper x-ref/kernel/printk.c x/kernel/printk.c
--- x-ref/kernel/printk.c	2003-08-26 00:13:17.000000000 +0200
+++ x/kernel/printk.c	2003-09-01 21:38:16.000000000 +0200
@@ -30,13 +30,13 @@
 #include <asm/uaccess.h>
 
 #if defined(CONFIG_MULTIQUAD) || defined(CONFIG_IA64)
-#define LOG_BUF_LEN	(65536)
+#define __LOG_BUF_LEN	(65536)
 #elif defined(CONFIG_ARCH_S390)
-#define LOG_BUF_LEN	(131072)
+#define __LOG_BUF_LEN	(131072)
 #elif defined(CONFIG_SMP)
-#define LOG_BUF_LEN	(32768)
+#define __LOG_BUF_LEN	(32768)
 #else	
-#define LOG_BUF_LEN	(16384)			/* This must be a power of two */
+#define __LOG_BUF_LEN	(16384)			/* This must be a power of two */
 #endif
 
 #define LOG_BUF_MASK	(LOG_BUF_LEN-1)
@@ -78,7 +78,9 @@ struct console *console_drivers;
  */
 static spinlock_t logbuf_lock = SPIN_LOCK_UNLOCKED;
 
-static char log_buf[LOG_BUF_LEN];
+static char __log_buf[__LOG_BUF_LEN];
+static char * log_buf = __log_buf;
+static int LOG_BUF_LEN = __LOG_BUF_LEN;
 #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
 
 /*
@@ -151,6 +153,39 @@ static int __init console_setup(char *st
 
 __setup("console=", console_setup);
 
+static int __init log_buf_len_setup(char *str)
+{
+	unsigned long size = simple_strtoul(str, &str, 0);
+
+	if (size & (size-1))
+		printk("log_buf_len: invalid size - needs a power of two\n");
+
+	spin_lock_irq(&logbuf_lock);
+	if (size > LOG_BUF_LEN) {
+		unsigned long start, end, dest_idx, offset;
+
+		LOG_BUF_LEN = size;
+		log_buf = alloc_exact(LOG_BUF_LEN);
+
+		offset = start = min(con_start, log_start);
+		end = log_end;
+		dest_idx = 0;
+		while (start != end) {
+			log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
+			start++;
+			dest_idx++;
+		}
+		log_start -= offset;
+		con_start -= offset;
+		log_end -= offset;
+	}
+	spin_unlock_irq(&logbuf_lock);
+
+	return 1;
+}
+
+__setup("log_buf_len=", log_buf_len_setup);
+
 /*
  * Commands to do_syslog:
  *

Andrea - If you prefer relying on open source software, check these links:
	    rsync.kernel.org::pub/scm/linux/kernel/bkcvs/linux-2.[45]/
	    http://www.cobite.com/cvsps/
	    svn://svn.kernel.org/linux-2.[46]/trunk