Re: [Qemu-devel] [PATCH 1/2] vmstate: Add helper to enable GHashTable migration

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/22/2014 08:57 PM, Alexander Graf wrote:
> 
> On 22.05.14 12:53, Alexey Kardashevskiy wrote:
>> This adds a VMSTATE_HASH_V macro. This implements put/get callbacks for it.
>> This implements a qemu_hash_init() wrapper to save key/value sizes.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>   include/migration/vmstate.h | 10 +++++++++
>>   include/qemu-common.h       | 13 +++++++++++
>>   vmstate.c                   | 54
>> +++++++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 77 insertions(+)
>>
>> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
>> index 7e45048..6af599d 100644
>> --- a/include/migration/vmstate.h
>> +++ b/include/migration/vmstate.h
>> @@ -166,6 +166,7 @@ extern const VMStateInfo vmstate_info_timer;
>>   extern const VMStateInfo vmstate_info_buffer;
>>   extern const VMStateInfo vmstate_info_unused_buffer;
>>   extern const VMStateInfo vmstate_info_bitmap;
>> +static const VMStateInfo vmstate_info_hash;
>>     #define type_check_2darray(t1,t2,n,m) ((t1(*)[n][m])0 - (t2*)0)
>>   #define type_check_array(t1,t2,n) ((t1(*)[n])0 - (t2*)0)
>> @@ -740,6 +741,15 @@ extern const VMStateInfo vmstate_info_bitmap;
>>   #define VMSTATE_BUFFER_UNSAFE(_field, _state, _version, _size)        \
>>       VMSTATE_BUFFER_UNSAFE_INFO(_field, _state, _version,
>> vmstate_info_buffer, _size)
>>   +#define VMSTATE_HASH_V(_field, _state, _version) {                      \
>> +    .name       = (stringify(_field)),                                  \
>> +    .version_id = (_version),                                           \
>> +    .size       = sizeof(qemu_hash),                                    \
>> +    .info       = &vmstate_info_hash,                                   \
>> +    .flags      = VMS_SINGLE,                                           \
>> +    .offset     = vmstate_offset_value(_state, _field, qemu_hash),      \
>> +}
>> +
>>   #define VMSTATE_UNUSED_V(_v, _size)                                   \
>>       VMSTATE_UNUSED_BUFFER(NULL, _v, _size)
>>   diff --git a/include/qemu-common.h b/include/qemu-common.h
>> index 3f3fd60..ee973e7 100644
>> --- a/include/qemu-common.h
>> +++ b/include/qemu-common.h
>> @@ -462,4 +462,17 @@ int parse_debug_env(const char *name, int max, int
>> initial);
>>     const char *qemu_ether_ntoa(const MACAddr *mac);
>>   +typedef struct qemu_hash {
>> +    GHashTable *hash;
>> +    int key_size;
>> +    int value_size;
>> +} qemu_hash;
>> +
>> +static inline void qemu_hash_init(qemu_hash *h, int key_size, int
>> value_size)
>> +{
>> +    h->key_size = key_size;
>> +    h->value_size = value_size;
>> +    h->hash = g_hash_table_new_full(g_int_hash, g_int_equal, g_free,
>> g_free);
>> +}
>> +
>>   #endif
>> diff --git a/vmstate.c b/vmstate.c
>> index b5882fa..2148e73 100644
>> --- a/vmstate.c
>> +++ b/vmstate.c
>> @@ -667,3 +667,57 @@ const VMStateInfo vmstate_info_bitmap = {
>>       .get = get_bitmap,
>>       .put = put_bitmap,
>>   };
>> +
>> +/* Save restore for qemu_hash which is a wrapper over GHashTable */
>> +static int get_hash(QEMUFile *f, void *pv, size_t size)
>> +{
>> +    qemu_hash *h = pv;
>> +    uint32_t num = g_hash_table_size(h->hash);
>> +    gpointer key, value;
>> +
>> +    num = qemu_get_be32(f);
>> +
>> +    for ( ; num; --num) {
>> +        int i;
>> +
>> +        key = g_malloc0(h->key_size);
>> +        for (i = 0; i < h->key_size; ++i) {
>> +            ((uint8_t *)key)[i] = qemu_get_byte(f);
>> +        }
>> +        value = g_malloc0(h->value_size);
>> +        for (i = 0; i < h->value_size; ++i) {
>> +            ((uint8_t *)value)[i] = qemu_get_byte(f);
>> +        }
>> +        g_hash_table_insert(h->hash, key, value);
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +static void put_hash(QEMUFile *f, void *pv, size_t size)
>> +{
>> +    qemu_hash *h = pv;
>> +    uint32_t num = g_hash_table_size(h->hash);
>> +    GHashTableIter iter;
>> +    gpointer key, value;
>> +
>> +    qemu_put_be32(f, num);
>> +
>> +    g_hash_table_iter_init(&iter, h->hash);
>> +    while (g_hash_table_iter_next (&iter, &key, &value)) {
>> +        int i;
>> +
>> +        for (i = 0; i < h->key_size; ++i) {
>> +            qemu_put_byte(f, ((uint8_t *)key)[i]);
>> +        }
>> +        for (i = 0; i < h->value_size; ++i) {
>> +            qemu_put_byte(f, ((uint8_t *)value)[i]);
> 
> I think the only way to do this safely would be to do a recursive
> introspective walk through the hash table's key and value properties. Every
> key and every property can be an object again, right?
>
> We would basically impose a limit onto ourselves that every member of the
> hash table would have to be a GObject again.

This is a bit too much for the task I am trying to solve :)

@key here is uin32_t and there is no point in making it an object...



-- 
Alexey