Re: [PATCH] report size of printk buffer

[Andries Brouwer <Andries.Brouwer@cwi.nl>]

On Wed, May 05, 2004 at 10:42:10PM +0200, Roman Zippel wrote:

> On Tue, 4 May 2004 Andries.Brouwer@cwi.nl wrote:
> 
> > In the old days the printk log buffer had a constant size,
> > and dmesg asked for the 4096, later 8192, later 16384 bytes in there.
> > These days the printk log buffer has variable size, and it is not
> > easy for dmesg to do the right thing, especially when doing a
> > "read and clear".
> 
> Why don't you simply change it into "read and clear read data"?
> E.g. something like below.
> 
> bye, Roman
> 
> Index: kernel/printk.c
> ===================================================================
> RCS file: /usr/src/cvsroot/linux-2.6/kernel/printk.c,v
> retrieving revision 1.1.1.6
> diff -u -p -r1.1.1.6 printk.c
> --- a/kernel/printk.c	11 Mar 2004 18:34:55 -0000	1.1.1.6
> +++ b/kernel/printk.c	5 May 2004 20:39:05 -0000
> @@ -305,7 +305,7 @@ int do_syslog(int type, char __user * bu
>  		if (count > logged_chars)
>  			count = logged_chars;
>  		if (do_clear)
> -			logged_chars = 0;
> +			logged_chars -= count;
>  		limit = log_end;
>  		/*

No, that is buggy.

If one asks for count bytes, one gets the last count bytes of output,
not the first.

Andries