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

[mdroth]

On Wed, Mar 13, 2013 at 03:07:52PM -0500, mdroth wrote:
> On Wed, Mar 13, 2013 at 06:10:30PM +0800, address@hidden wrote:
> > From: Lei Li <address@hidden>
> > 
> > Signed-off-by: Lei Li <address@hidden>
> > ---
> >  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?

Actually, do we even need malloc? Can't be just allocate SYSTEMTIME
struct on the stack and pass a pointer to GetSystemTime?

> 
> > +   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().
> 
> > +       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)
> 
> > +
> > +   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
> >