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Re: [Qemu-devel] [PATCH] qemu-ga-win: Document 'guest-set-time' limitati
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH] qemu-ga-win: Document 'guest-set-time' limitation |
Date: |
Tue, 20 Jan 2015 10:11:32 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
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 <address@hidden>
> ---
> 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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