Re: [PATCH v3] migration: Support gtree migration

[Peter Xu]

On Thu, Oct 10, 2019 at 02:11:46PM +0200, Auger Eric wrote:
> >>> Also, should we avoid using UINT in all cases?  But of course if we
> >>> start to use VMSTATE_UINT32_V then we don't have this issue.
> >> Depending on the clarification of above point, maybe I can rename
> >> VMSTATE_GTREE_DIRECT_KEY_V into VMSTATE_GTREE_DIRECT_UINT_KEY_V
> >>
> >> direct keys seem to be more common for hash tables actually.
> >> https://developer.gnome.org/glib/stable/glib-Hash-Tables.html#g-hash-table-new-full
> >>
> >> There are stand conversion macros to/from int, uint, size
> >> https://developer.gnome.org/glib/stable/glib-Type-Conversion-Macros.html
> > 
> > Yeh it's fine to use direct keys.  Though my question was more about
> > "unsigned int" - here when we put, we cast a pointer into unsigned
> > int, which can be 2/4 bytes, IIUC.  I'm thinking whether at least we
> > should use direct cast (e.g., (uint32_t)ptr) to replace
> > GPOINTER_TO_UINT() to make sure it's 4 bytes.  Futher, maybe we should
> > start with uint64_t here in the migration stream, otherwise we should
> > probably drop the high 32 bits if we migrate a gtree whose key is 64
> > bits long (and since we're working with migration we won't be able to
> > change that in the future for compatibility reasons...).
> > 
> > Summary:
> > 
> > Maybe we can replace:
> > 
> >     qemu_put_be32(f, GPOINTER_TO_UINT(key)); /* direct key */
> > 
> > To:
> > 
> >     qemu_put_be64(f, (uint64_t)key); /* direct key */
> > 
> > And apply similar thing to get() side?
> 
> This was my first idea as well but I got stuck with a mingw compilation
> issues if I remember correctly, trying to cast pointers to a wrong sized
> uint. This got removed by using the GPOINTER_TO_UINT conversion functions.

#define GPOINTER_TO_UINT(p) ((guint) (gulong) (p))

Could "(uint64_t)(uintptr_t)pointer" do the work?

Thanks,

-- 
Peter Xu