[Crash-utility] [Patch-v2] Fix handling the ring buffer for 'log' command.

[Ken'ichi Ohmichi]

Hi Dave,

Thank you for your comment.

Dave Anderson wrote:
>>>>>> So my initial leaning would be to continue to show what's actually there.
>>>>>> I trust myself as a crash analyzer more than I trust the administrator. 
>>>>>>
>>>>>> But I could be convinced otherwise.
>>>>>>
>>>>>> What do others on the list think about this?
>>>> I would much rather see all of the contents of the log buffer.
>> OK, I attach a new patch for outputing all of the contents of the log
>> buffer. How about this patch ?
> 
> It appears to works OK, although the leftover references to "logged_chars"
> should be removed from your patch, correct?

Yes, you are right. "logged_chars" is not referred by my patch,
and it should be removed. This is a new patch for removing it.


Thanks
Ken'ichi Ohmichi

---
[Patch-v3] Fix handling the ring buffer for 'log' command.

Changelog of v3:
 - Removing the references to "logged_chars".

Changelog of v2:
 - Extending the output range of 'log' command to all the ring buffer.

I found there is a 'log' command problem related to handling the ring
buffer, and this patch fixes it.

The ring buffer can be cleared by klogctl(2) from a user process, but
current crash utility does not consider this case. The following output
of current crash utility is example of this case. You see there are some
messages after the panic message. These messages are the oldest log data,
so they should be output first.

  crash > log
  [snip]
  exception[8291] trap divide error rip:4004c0 rsp:7fffb56cdf60 error:0
  exception[8293] trap divide error rip:4004c0 rsp:7fffbb0628f0 error:0
  SysRq : Trigger a crashdump
   14 15) *0, disabled.
  ACPI: PCI Interrupt Link [LNKF] (IRQs 4 5 6 7 10 14 15) *0, disabled.
  ACPI: PCI Interrupt Link [LNKG] (IRQs 3 4 5 6 7 10 14 15) *0, disabled.
  [snip]
  crash >

This patch fixes this invalid output to the folloing:

  crash > log
   14 15) *0, disabled.
  ACPI: PCI Interrupt Link [LNKF] (IRQs 4 5 6 7 10 14 15) *0, disabled.
  ACPI: PCI Interrupt Link [LNKG] (IRQs 3 4 5 6 7 10 14 15) *0, disabled.
  [snip]
  exception[8291] trap divide error rip:4004c0 rsp:7fffb56cdf60 error:0
  exception[8293] trap divide error rip:4004c0 rsp:7fffbb0628f0 error:0
  SysRq : Trigger a crashdump
  crash>

Signed-off-by: Ken'ichi Ohmichi <oomichi at mxs.nes.nec.co.jp>
---
--- crash-4.0-7.7/kernel.c.orig	2009-02-06 01:13:43.000000000 +0900
+++ crash-4.0-7.7/kernel.c	2009-02-19 08:40:00.000000000 +0900
@@ -3365,7 +3365,7 @@ void 
 dump_log(int msg_level)
 {
 	int i;
-	ulong log_buf, logged_chars;
+	ulong log_buf, log_end;
 	char *buf;
 	char last;
 	ulong index;
@@ -3392,18 +3392,16 @@ dump_log(int msg_level)
 
 	buf = GETBUF(log_buf_len);
 	log_wrap = FALSE;
-	get_symbol_data("logged_chars", sizeof(ulong), &logged_chars);
+	get_symbol_data("log_end", sizeof(ulong), &log_end);
         readmem(log_buf, KVADDR, buf,
         	log_buf_len, "log_buf contents", FAULT_ON_ERROR);
 
-	if (logged_chars < log_buf_len) {
+	if (log_end < log_buf_len)
 		index = 0;
-	} else {
-		get_symbol_data("log_end", sizeof(ulong), &index);
-		index &= log_buf_len-1;
-	} 
+	else
+		index = log_end & (log_buf_len - 1);
 
-	if ((logged_chars < log_buf_len) && (index == 0) && (buf[index] == '<'))
+	if ((log_end < log_buf_len) && (index == 0) && (buf[index] == '<'))
 		loglevel = TRUE;
 	else
 		loglevel = FALSE;