Messages in this thread Patch in this message | | | Subject | Re: [PATCH 2/2] Save current timestamp part of dmesg while writing oops message to pstore | From | Ankit Kumar <> | Date | Tue, 23 May 2017 14:19:47 +0530 |
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Hi Kees,
On Tuesday 23 May 2017 05:21 AM, Kees Cook wrote: > On Mon, May 22, 2017 at 3:20 AM, Ankit Kumar <ankit@linux.vnet.ibm.com> wrote: >> 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] > While I understand your rationale about possibly losing file timestamp > information in userspace, I think this is a solvable problem on the > collection side. If an additional header is needed, perhaps copy the > dmesg files like this: > > for i in dmesg-*; do > (stat --format=%y /sys/fs/pstore/$i; \ > cat /sys/fs/pstore/$i) > $collect_dir/$i > done
Yes. We can handle this in userspace. But we wanted to see if we can add this as part of pstore log itself.
> One of the primary concerns for pstore is the stored dump size,
I understand. How about adding timestamp to file name itself? Something like below
index 792a4e5..0837365 100644 --- a/fs/pstore/inode.c +++ b/fs/pstore/inode.c @@ -349,9 +349,10 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
switch (record->type) { case PSTORE_TYPE_DMESG: - scnprintf(name, sizeof(name), "dmesg-%s-%lld%s", + scnprintf(name, sizeof(name), "dmesg-%s-%lld%s-%lu.%lu", record->psi->name, record->id, - record->compressed ? ".enc.z" : ""); + record->compressed ? ".enc.z" : "", + record->time.tv_sec, record->time.tv_nsec / 1000); break; case PSTORE_TYPE_CONSOLE:
~Ankit
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