Hi Peter, On 10/10/19 1:35 PM, Peter Xu wrote: > On Thu, Oct 10, 2019 at 09:57:01AM +0200, Auger Eric wrote: >>>> +static gboolean put_gtree_elem(gpointer key, gpointer value, gpointer >>>> data) >>>> +{ >>>> + struct put_gtree_data *capsule = (struct put_gtree_data *)data; >>>> + QEMUFile *f = capsule->f; >>>> + int ret; >>>> + >>>> + qemu_put_byte(f, true); >>>> + >>>> + /* put the key */ >>>> + if (!capsule->key_vmsd) { >>>> + qemu_put_be32(f, GPOINTER_TO_UINT(key)); /* direct key */ >>> >>> This is special code path for direct key case. Can we simply define >>> VMSTATE_GTREE_DIRECT_KEY_V() somehow better so that it just uses the >>> VMSTATE_UINT32_V() as the key vmsd? Then iiuc vmstate_save_state() >>> could work well with that too. >> if the key_vmsd is a VMSTATE_UINT32_V then I understand >> vmstate_save_state(f, capsule->key_vmsd, key, capsule->vmdesc) >> expects key to be a pointer to a uint32. But in that case of direct key, >> it is a uint32. I don't figure out how to use vmstate_save_state in your >> proposal. > > Ah I see the point. And indeed I can't think of a better way now > (e.g., maybe I will always try to use GTrees with malloc()ed keys to > be simple when I want to migrate a gtree, but yeah that's not a reason > to refuse this patch :). > > Though we should be very careful on defining vmsds for GTrees in the > future with the help of this patch, and we must have the type (either > direct or not) to match the real usage of the tree otherwise QEMU can > potentially unreference the constant as a pointer. > >> >>> >>> 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. Thanks Eric > > Thanks, >