Re: [Qemu-devel] [PATCH 1/2] qga: add windows implementation for guest-get-time

[Lei Li <lilei@linux.vnet.ibm.com>]

On 03/14/2013 04:07 AM, mdroth wrote:
> On Wed, Mar 13, 2013 at 06:10:30PM +0800, lilei@linux.vnet.ibm.com wrote:
>> From: Lei Li <lilei@linux.vnet.ibm.com>
>>
>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>> ---
>>   qga/commands-win32.c |   32 ++++++++++++++++++++++++++++++++
>>   1 files changed, 32 insertions(+), 0 deletions(-)
>>
>> diff --git a/qga/commands-win32.c b/qga/commands-win32.c
>> index 7e8ecb3..0a2bb34 100644
>> --- a/qga/commands-win32.c
>> +++ b/qga/commands-win32.c
>> @@ -22,6 +22,12 @@
>>   #define SHTDN_REASON_FLAG_PLANNED 0x80000000
>>   #endif
>>
>> +/* multiple of 100 nanoseconds elapsed between windows baseline
>> +   (1/1/1601) and Unix Epoch (1/1/1970), accounting for leap years */
>> +#define W32_FT_OFFSET (10000000ULL * 60 * 60 * 24 * \
>> +                       (365 * (1970 - 1601) +       \
>> +                        (1970 - 1601) / 4 - 3))
>> +
>>   static void acquire_privilege(const char *name, Error **err)
>>   {
>>       HANDLE token;
>> @@ -108,6 +114,32 @@ void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
>>       }
>>   }
>>
>> +int64_t qmp_guest_get_time(Error **errp)
>> +{
>> +   SYSTEMTIME *ts = g_malloc0(sizeof(SYSTEMTIME));
> Don't we need to free this at some point?
>
Sorry, my fault here...

>> +   int64_t time_ns;
>> +   union {
>> +       UINT64 ns100;
>> +       FILETIME tf;
>> +   } time;
>> +
>> +   GetSystemTime(ts);
>> +   if (!ts) {
>> +       slog("guest-get-time failed: %d", GetLastError());
> GetSystemTime() does not seem to set an error that can be retrieved by
> GetLastError().

Yes, you are right.

>> +       error_setg_errno(errp, errno, "Failed to get time");
>> +       return -1;
>> +   }
>> +
>> +   if (!SystemTimeToFileTime(ts, &time.tf)) {
>> +       error_setg_errno(errp, errno, "Failed to convert system time");
>> +       return -1;
>> +   }
>> +
>> +   time_ns = (int64_t)((time.ns100 - W32_FT_OFFSET) * 100);
> I'm not sure how safe this union stuff is. The documentation suggests that in
> some circumstances the low/high fields in FILETIME might be padded for
> 64-bit alignment and that doing this type of cast could generate an
> alignment fault:
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/ms724284(v=vs.85).aspx
>
> or it might, perhaps even worse, just silently report the wrong time.
>
> I think we should just do the math explicitly:
>
> (((tf.dwHighDateTime << 32) | tf.dwLowDateTime) - W32_FT_OFFSET) * 100)
>
> (or something along that line)

OK, thanks.

>> +
>> +   return time_ns;
>> +}
>> +
>>   int64_t qmp_guest_file_open(const char *path, bool has_mode, const char *mode, Error **err)
>>   {
>>       error_set(err, QERR_UNSUPPORTED);
>> -- 
>> 1.7.7.6
>>


-- 
Lei