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

[Vivek Goyal]

On Tue, Jan 27, 2009 at 12:12:11AM -0800, Andrew Morton wrote:
> On Tue, 20 Jan 2009 10:22:56 -0500 Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> 
> > 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@xxxxxxxxxx>
> > 
> 
> I rewrote the title to
> 
> 	kexec: add dmesg log symbols to /proc/vmcoreinfo lists
> 
> it's nice to identify which subsystem is responsible for a patch.
> 
> I also did all the below.  Please check it.  (Is anyone else reading all
> this stuff??)
> 
> 
> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> 
> - switch didnt-need-to-be-a-macro to inline
> 
> - Remove unneeded ifdefs (we already did that in the header)
> 
> - repair bouncy enter key
> 
> Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
> Cc: Simon Horman <horms@xxxxxxxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
> 
Hi Andrew,

This looks good. I should have altleast caught unnecessary #ifdefs.:-(

Thanks
Vivek
 
>  include/linux/kernel.h |    5 ++++-
>  kernel/kexec.c         |    2 --
>  kernel/printk.c        |    1 -
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff -puN include/linux/kernel.h~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix include/linux/kernel.h
> --- a/include/linux/kernel.h~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix
> +++ a/include/linux/kernel.h
> @@ -254,7 +254,10 @@ static inline int printk_ratelimit(void)
>  static inline bool printk_timed_ratelimit(unsigned long *caller_jiffies, \
>  					  unsigned int interval_msec)	\
>  		{ return false; }
> -#define log_buf_kexec_setup() do {} while(0)
> +
> +static inline void log_buf_kexec_setup(void)
> +{
> +}
>  #endif
>  
>  extern int printk_needs_cpu(int cpu);
> diff -puN kernel/kexec.c~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix kernel/kexec.c
> --- a/kernel/kexec.c~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix
> +++ a/kernel/kexec.c
> @@ -1409,9 +1409,7 @@ static int __init crash_save_vmcoreinfo_
>  	VMCOREINFO_OFFSET(list_head, prev);
>  	VMCOREINFO_OFFSET(vm_struct, addr);
>  	VMCOREINFO_LENGTH(zone.free_area, MAX_ORDER);
> -#ifdef CONFIG_PRINTK
>  	log_buf_kexec_setup();
> -#endif
>  	VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES);
>  	VMCOREINFO_NUMBER(NR_FREE_PAGES);
>  	VMCOREINFO_NUMBER(PG_lru);
> diff -puN kernel/printk.c~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix kernel/printk.c
> --- a/kernel/printk.c~kexec-add-dmesg-log-symbols-to-proc-vmcoreinfo-lists-fix
> +++ a/kernel/printk.c
> @@ -143,7 +143,6 @@ void log_buf_kexec_setup(void)
>  	VMCOREINFO_SYMBOL(log_end);
>  }
>  
> -
>  static int __init log_buf_len_setup(char *str)
>  {
>  	unsigned size = memparse(str, &str);
> _
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