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

[Neil Horman]

On Thu, Feb 05, 2009 at 09:23:22AM +0900, Ken'ichi Ohmichi wrote:
> 
> Hi Neil,
> 
> Thank you for a kernel patch and a makedumpfile patch.
> 
> Neil Horman wrote:
> >> That aside we aren't currently exporting log_buf_len, so I don't
> >> think this code works actually works.
> >>
> >> Neil can you add a comment in kernel/printk.c of the algorithm
> >> necessary for external tools to decode the ring buffer?
> >>
> >> We need the comment because people working on kernel/printk.c
> >> need to know what is happening and without having to review lots
> >> of user space code, and we need the comment to verify that we
> >> are exporting the right things.
> >>
> > 
> > Ok, as per Erics comment, I've written this.  It applies on top of whats already
> > in your tree Andrew.  It adds some comments on the function in question so that
> > anyone working on printk.c will know why we're exporting their symbols.  It also
> > modifies slightly the symbols we are exporting so that we can handle dmesg
> > buffers that are longer than the standard PAGE_SIZE configuration, and lets us
> > detect and handle buffer wraps.
> > 
> > Thanks!
> > 
> > printk.c |   12 +++++++++++-
> > 1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
> > 
> > diff --git a/kernel/printk.c b/kernel/printk.c
> > index dd5cc7b..6a1163b 100644
> > --- a/kernel/printk.c
> > +++ b/kernel/printk.c
> > @@ -138,10 +138,20 @@ static int log_buf_len = __LOG_BUF_LEN;
> >  static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
> >  
> >  #ifdef CONFIG_KEXEC
> > +/*
> > + * This appends the listed symbols to /proc/vmcoreinfo
> > + * /proc/vmcoreinfo is used by various utiilties, like
> > + * crash and makedumpfile to obtain access to symbols that
> > + * are otherwise very difficult to locate.  These symbols 
> > + * are specifically used so that utilities 
> > + * can access and extract the dmesg log from a vmcore file
> > + * after a crash
> > + */
> >  void log_buf_kexec_setup(void)
> >  {
> >  	VMCOREINFO_SYMBOL(log_buf);
> > -	VMCOREINFO_SYMBOL(log_end);
> > +	VMCOREINFO_SYMBOL(log_buf_len);
> > +	VMCOREINFO_SYMBOL(logged_chars)
> >  }
> >  #endif
> 
> Please do not remove VMCOREINFO_SYMBOL(log_end), because makedumpfile
> needs it for knowing the latest log offset in ring buffer of dmesg.
> I updated a makedumpfile patch for handling ring buffer, and it is
> possible to download the latest patch from the following site:
> 
> https://sourceforge.net/tracker2/download.php?group_id=178938&atid=887142&file_id=312113&aid=2521075
> 
Understood, new patch attached.

Add some comments and extra symbols on top of whats there for kernel/printk.c to
satisfy Erics requests, and support Ken'ichi's enhanced version of the
makedumpfile patch

Neil

Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>



 printk.c |   11 +++++++++++
 1 file changed, 11 insertions(+)


diff --git a/kernel/printk.c b/kernel/printk.c
index dd5cc7b..6c25eba 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -138,10 +138,21 @@ static int log_buf_len = __LOG_BUF_LEN;
 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
 
 #ifdef CONFIG_KEXEC
+/*
+ * This appends the listed symbols to /proc/vmcoreinfo
+ * /proc/vmcoreinfo is used by various utiilties, like
+ * crash and makedumpfile to obtain access to symbols that
+ * are otherwise very difficult to locate.  These symbols 
+ * are specifically used so that utilities 
+ * can access and extract the dmesg log from a vmcore file
+ * after a crash
+ */
 void log_buf_kexec_setup(void)
 {
 	VMCOREINFO_SYMBOL(log_buf);
 	VMCOREINFO_SYMBOL(log_end);
+	VMCOREINFO_SYMBOL(log_buf_len);
+	VMCOREINFO_SYMBOL(logged_chars)
 }
 #endif
 
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