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Re: [Qemu-devel] [RFC] Can we convert UTC time to local time in Qemu

From: Eric Blake
Subject: Re: [Qemu-devel] [RFC] Can we convert UTC time to local time in Qemu
Date: Wed, 20 May 2015 08:43:45 -0600
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On 05/20/2015 12:29 AM, Gonglei (Arei) wrote:
> Hi,
> At present, Qemu use g_time_val_to_iso8601() to get the UTC added to 
> error_report()
> (commit 5e2ac5191), TBH this way is very simply, we just need invoke standard 
> glib functions to
> complete the job. 

local time is ambiguous (daylight savings, and even consider what
happens when you physically relocate your machine to a different time
zone).  UTC is better.

> But in the cloud computing and data center scenarios, there are many
> Other open source components, such as kernel, libvirt, openstack which are 
> all using local time
> to record the message logs, only Qemu is using the UTC time. When we want to 
> find a error
> message of Qemu, we should convert the UTC time to local time manually, and 
> unfortunately
> different countries have different local time, what a trouble thing the 
> converting is.
> So, my question is: Can we convert the UTC time to local time in Qemu? 

Actually, libvirt uses UTC on purpose, not only because it is
unambiguous, but because it prints timestamps even in situations where
it must be async-signal safe, and there is no async-signal-safe way to
determine the offset required to convert UTC to local time.

> Any thoughts? Thanks.

I'd rather stick with UTC in logs (but perhaps make it more obvious that
the timestamp is UTC by actually sticking that string as part of the
timestamp - libvirt is not currently doing that).

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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