[PATCH]: add dmesg log symbols to /proc/vmcoreinfo lists

Vivek Goyal vgoyal at redhat.com
Tue Jan 20 10:22:56 EST 2009

On Tue, Jan 20, 2009 at 10:09:58AM -0500, Neil Horman wrote:
> On Tue, Jan 20, 2009 at 09:15:51AM -0500, Vivek Goyal wrote:
> > On Mon, Jan 19, 2009 at 04:21:27PM -0500, Neil Horman wrote:
> > > Hey all-
> > > 	It would be nice to be able to extract the dmesg log from a vmcore file
> > > without needing to keep the debug symbols for the running kernel handy all the
> > > time.  We have a facility to do this in /proc/vmcore.  This patch adds the
> > > log_buf and log_end symbols to the vmcoreinfo area so that tools (like
> > > makedumpfile) can easily extract the dmesg logs from a vmcore image.
> > > 
> > 
> > It would be nice to get dmesg log if debug symbols are not around. Can't
> > we use System.map for getting symbol addresses? vmcoreinfo had started
> > small and seems to be growing now. I am thinking down the line will making
> > use of System.map for such cases make sense?
> > 
> System.map only include exported and public symbols.  log_buf and log_end are
> static, and not reported in the System.map.  Its a nice idea, but not
> comprehensive for everything in the kernel.
> ><snip>
> > 
> > Will it be an issue if we make log_buf and log_end non static and directly
> > access these in kexec.c?
> > 
> I had considered that, but was a bit hesitant to do so, since it exposes the
> internal implementation of the dmesg buffer.  In the event someone disables
> CONFIG_PRINTK, thats just more code we need to ifdef.  With this implementation
> we just stub out the log_buf_setup function, and let that be that.  It seems
> more consice to me this way.

Makes sense to me.

Acked-by: Vivek Goyal <vgoyal at redhat.com>


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