Re: [Qemu-devel] [PATCH] qemu-ga-win: Document 'guest-set-time' limitation

[Eric Blake <eblake@redhat.com>]

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On 01/20/2015 01:30 AM, Michal Privoznik wrote:
> The command implementation for Windows guest has this limitation. If
> no time to set has been provided the documentation for the command
> states that time should be read from RTC. However, on Windows bare
> GetSystemTime() is used, which does not read anything from RTC rather
> than return system time. Yeah, that system time which is wrong (after
> stop & cont) and which we want to set.
> 
> However, there's no simple way to read RTC on windows yet [1], so
> until the time somebody comes with bright implementation, we should at
> least document the command implementation limitation.

I think it would be wiser to update the Windows guest-agent code to
explicitly fail instead of calling a useless GetSystemTime(), if we
can't meet the documented semantics of calling the function without a
timestamp.

> 
> 1: http://msdn.microsoft.com/en-us/library/aa908981.aspx
> 
> Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
> ---
>  qga/qapi-schema.json | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
> index 376e79f..91821ef 100644
> --- a/qga/qapi-schema.json
> +++ b/qga/qapi-schema.json
> @@ -121,7 +121,10 @@
>  # given value, then sets the Hardware Clock (RTC) to the
>  # current System Time. This will make it easier for a guest
>  # to resynchronize without waiting for NTP. If no @time is
> -# specified, then the time to set is read from RTC.
> +# specified, then the time to set is read from RTC. On Windows
> +# guests there's implementation limitation that does not read the
> +# time from RTC if no time has been provided. Users are advised
> +# to allways pass a value for Windows guests.

Grammar is awkward, and there's a typo in 'allways'.  If we are okay
with just a doc change (although I argued above that we really should
have a code change), then I'd go with something more like:

In the current implementation, Windows guests are unable to read time
from the RTC, so users are advised to always pass a value.

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


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