Re: [Freeipmi-devel] [bug #38798] timestamps are interpretted as UT rather than localtime, violating IPMI 2.0 section 37

[Liebig, Holger]

> 
> I for one think that's a great idea. Do you happen to know of BMCs which
> actually support the "Get SEL Time UTC Offset" command?
[Liebig, Holger] 
I know at least one BMC base firmware provider which supports these 2 optional 
IPMI cmds in current firmware versions. But (unfortunately) logs by default 
into the SEL with local time timestamps and in addition provides the UTC offset 
of the running embedded O/S with the Get SEL Time UTC cmd - which in my opinion 
is not correct. A BMC should log either in local time or in UTC and provide 
information about the current UTC offset of the SEL in the latter case, but not 
both at the same time.

My understanding is: 
Get SEL Time UTC Offset not supported or returning unspecified (0x7FFF) the SEL 
is operating in local time. Any other value within the valid range of -1440 ... 
1400 is indicating the SEL running in UTC mode. Adding the offset to the SEL 
timestamps results in calendar time, quote from the man page: "When interpreted 
as an absolute time value, it represents the number of seconds elapsed since 
the Epoch, 1970-01-01 00:00:00 +0000 (UTC)". Both localtime_r() and gmtime_r() 
take calendar time as input, which would represents your usage model of 
converting #1 into #2 or #3 below. 
 
> 
> One point of frequent confusion is that there are actually 3 potential
> interpretations of a time-stamp:
> 1. Local time for the managed system/BMC 2. Local time for the management
> console 3. UTC
[Liebig, Holger] 
It can be even more complicated, depending if the BMC has its own RTC/time 
source (better), or is using the systems RTC (bad). If the BMC is using the 
system RTC and depending on the O/S and the configuration of the system, the 
system RTC can reflect local time (Windows default) or UTC (Linux default). 
This can be changed for both of them to match each other, but the default is 
vice versa and dual booting is fun. See also 
http://mikebeach.org/2011/04/10/windows-linux-dual-boot-system-time-issues/ . 
Additional problems arise, when the O/S is operating the system RTC in UTC 
mode, but the BMC is interpreting the RTC as local time without a standard way 
of knowledge of the RTC mode of the running O/S. So we might end up with 
multiple command line options:

--interpret-sel-time-as-localtime: 
If "Get SEL UTC offset" returns unspecified or is not supported pass the 
timestamp unmodified into gmtime_r()
If "Get SEL UTC offset" valid pass the timestamp + offset into localtime_r()

--interpret-sel-time-as-utc
If "Get SEL UTC offset" returns unspecified or is not supported pass the 
timestamp unmodified into localtime_r()
If "Get SEL UTC offset" valid pass the timestamp + offset into gmtime_r()

--ignore-sel-time-utc-offset
Workaround for the case mentioned above when the BMC is logging with local time 
timestamps and is also returning a valid SEL Time UTC offset. --> pass the 
timestamp unmodified into gmtime_r()

And the combinations:
--interpret-sel-time-as-utc --ignore-sel-time-utc-offset
??? use UTC offset from management console?

--interpret-sel-time-as-localtime --ignore-sel-time-utc-offset
pass the timestamp unmodified into gmtime_r()

> 
> The IPMI specification defines time-stamps sent from the management
> controller as format #1. If the management console can get the managed
> system's UTC offset (e.g. using "Get SEL Time UTC Offset"), then it could
> convert the timestamps from format #1 to either #2 or #3 (for display,
> storage or comparison purposes).

[Liebig, Holger] 
As I stated above, my understanding is that this command is for solely for the 
SEL Time UTC offset and **not** a generic "Get BMC Time UTC offset". 


Let me know if you have comments or input regarding this.

Thanks,
Holger

> 
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf Of
> Liebig, Holger
> Sent: Thursday, April 25, 2013 10:51 PM
> To: address@hidden
> Subject: Re: [Freeipmi-devel] [bug #38798] timestamps are interpretted as
> UT rather than localtime, violating IPMI 2.0 section 37
> 
> Al,
> If this gets fixed (and if possible) could you please include handling of
> the optional Get SEL Time UTC offset command introduced in Errata 4? This
> can be used to convert non localtime timestamps back to calendar time and
> come in handy when a BMC is configured to use a NTP server. From calendar
> time you can then convert it to localtime or UTC using the appropriate
> libc functions (localtime_r() and gmtime_r()). And as generic improvement:
> customers with BMC's around the world might appreciate a command line
> option to display SEL timestamps in GMT in addition to localtime in order
> to correlate events to each other.
> 
> Thanks,
> Holger
>