linux-kernel - [PATCH 2/2] Save current timestamp part of dmesg while writing oops message to pstore

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Date:   Mon, 22 May 2017 15:50:37 +0530
From:   Ankit Kumar <ankit@...ux.vnet.ibm.com>
To:     keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com
Cc:     linux-kernel@...r.kernel.org, mahesh@...ux.vnet.ibm.com,
        hbathini@...ux.vnet.ibm.com, hegdevasant@...ux.vnet.ibm.com,
        ankit@...ux.vnet.ibm.com
Subject: [PATCH 2/2] Save current timestamp part of dmesg while writing oops message to pstore

Currently on panic or Oops, kernel saves the last few bytes from dmesg
buffer to nvram. Usually kdump does capture kernel memory and provide
dmesg logs as well. But in some cases where kdump fails to capture
vmcore, the dmesg buffer stored in nvram/pstore turns out to be very
helpful in analyzing root cause.

Present code creates pstore dump file(/sys/fs/pstore/dmesg-***) based on
timestamp(retrieved from header). Current pstore code creates dump file
(/sys/fs/pstore/dmesg-***) with that timestamp. Dump file can be analyzed
based on file creation time and we can make out whether dump file has latest
data or not.

But when we transfer pstore dump file(/sys/fs/pstore/dmesg-***) to other
machine or collect file using some utilities(sosreport/supportconfig) then file
timestamp gets changed and hence by looking at device file (dmesg-***) we won't
be able to identify whether dump has latest data or not.

Above issue can be fixed if we also have timestamp(dump creation time) as
initial few bytes while capturing dmesg buffer to pstore dump file
(/sys/fs/pstore/dmesg-***).

This patch enhances pstore write code to also write timestamp as part of data.

Here is sample log of dump file:(/sys/fs/pstore/dmesg-***)
Oops#1 Part1 [timestamp:1494939359.590463]

Above timestamp can be converted to current zone using date command.
 #date -d @1494939359.590463
 # Tue May 16 18:25:59 IST 2017

Signed-off-by: Ankit Kumar <ankit@...ux.vnet.ibm.com>
---
 fs/pstore/platform.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 4fedf83..f65000e 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -501,6 +501,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 	unsigned long	flags = 0;
 	int		is_locked;
 	int		ret;
+	struct timespec timestamp;

 	why = get_reason_str(reason);

@@ -540,9 +541,11 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 			dst_size = psinfo->bufsize;
 		}

+		pstore_get_timestamp(&timestamp);
 		/* Write dump header. */
-		header_size = snprintf(dst, dst_size, "%s#%d Part%u\n", why,
-				 oopscount, part);
+		header_size = snprintf(dst, dst_size, "%s#%d Part%u [timestamp:%lu.%lu]\n",
+				why, oopscount, part, (long)timestamp.tv_sec,
+				(long)(timestamp.tv_nsec / 1000));
 		dst_size -= header_size;

 		/* Write dump contents. */
-- 
2.7.4