On Sat, May 20, 2023 at 9:36 AM Marc-André Lureau <
marcandre.lur...@gmail.com> wrote:
> Hi
>
> On Thu, May 18, 2023 at 4:03 PM Albert Esteve <aest...@redhat.com> wrote:
>
>> Add hash and an equal function to uuid module.
>>
>> Add a couple simple unit tests for new functions,
>> checking collisions for similar UUIDs in the case
>> of the hash function, and comparing generated UUIDs
>> for the equal function.
>>
>> Signed-off-by: Albert Esteve <aest...@redhat.com>
>> ---
>> include/qemu/uuid.h | 4 ++++
>> tests/unit/test-uuid.c | 46 ++++++++++++++++++++++++++++++++++++++++++
>> util/uuid.c | 38 ++++++++++++++++++++++++++++++++++
>> 3 files changed, 88 insertions(+)
>>
>> diff --git a/include/qemu/uuid.h b/include/qemu/uuid.h
>> index dc40ee1fc9..136df682c9 100644
>> --- a/include/qemu/uuid.h
>> +++ b/include/qemu/uuid.h
>> @@ -96,4 +96,8 @@ int qemu_uuid_parse(const char *str, QemuUUID *uuid);
>>
>> QemuUUID qemu_uuid_bswap(QemuUUID uuid);
>>
>> +uint32_t qemu_uuid_hash(const void *uuid);
>> +
>> +int qemu_uuid_equal(const void *lhv, const void *rhv);
>>
>
> There is already qemu_uuid_is_equal()
>
>
Agh, true. I'll remove it. Not sure why my brain ignored it as I was
reading the code...
> +
>> #endif
>> diff --git a/tests/unit/test-uuid.c b/tests/unit/test-uuid.c
>> index c111de5fc1..8c865869d5 100644
>> --- a/tests/unit/test-uuid.c
>> +++ b/tests/unit/test-uuid.c
>> @@ -171,6 +171,50 @@ static void test_uuid_unparse_strdup(void)
>> }
>> }
>>
>> +static void test_uuid_hash(void)
>> +{
>> + QemuUUID uuid;
>> + int i;
>> +
>> + for (i = 0; i < 100; i++) {
>> + qemu_uuid_generate(&uuid);
>> + /* Obtain the UUID hash */
>> + uint32_t hash_a = qemu_uuid_hash(&uuid);
>> + int data_idx = g_random_int_range(0, 15);
>> + /* Change a single random byte of the UUID */
>> + if (uuid.data[data_idx] < 0xFF) {
>> + uuid.data[data_idx]++;
>> + } else {
>> + uuid.data[data_idx]--;
>> + }
>> + /* Obtain the UUID hash again */
>> + uint32_t hash_b = qemu_uuid_hash(&uuid);
>> + /*
>> + * Both hashes shall be different (avoid collision)
>> + * for any change in the UUID fields
>> + */
>> + g_assert_cmpint(hash_a, !=, hash_b);
>> + }
>> +}
>> +
>> +static void test_uuid_equal(void)
>> +{
>> + QemuUUID uuid_a, uuid_b, uuid_c;
>> + int i;
>> +
>> + for (i = 0; i < 100; i++) {
>> + qemu_uuid_generate(&uuid_a);
>> + qemu_uuid_generate(&uuid_b);
>> + memcpy(&uuid_c, &uuid_a, sizeof(uuid_a));
>> +
>> + g_assert(qemu_uuid_equal(&uuid_a, &uuid_a));
>> + g_assert(qemu_uuid_equal(&uuid_b, &uuid_b));
>> + g_assert(qemu_uuid_equal(&uuid_a, &uuid_c));
>> + g_assert_false(qemu_uuid_equal(&uuid_a, &uuid_b));
>> + g_assert_false(qemu_uuid_equal(NULL, NULL));
>> + }
>> +}
>> +
>> int main(int argc, char **argv)
>> {
>> g_test_init(&argc, &argv, NULL);
>> @@ -179,6 +223,8 @@ int main(int argc, char **argv)
>> g_test_add_func("/uuid/parse", test_uuid_parse);
>> g_test_add_func("/uuid/unparse", test_uuid_unparse);
>> g_test_add_func("/uuid/unparse_strdup", test_uuid_unparse_strdup);
>> + g_test_add_func("/uuid/hash", test_uuid_hash);
>> + g_test_add_func("/uuid/equal", test_uuid_equal);
>>
>> return g_test_run();
>> }
>> diff --git a/util/uuid.c b/util/uuid.c
>> index b1108dde78..efa9b0a0e4 100644
>> --- a/util/uuid.c
>> +++ b/util/uuid.c
>> @@ -16,6 +16,7 @@
>> #include "qemu/osdep.h"
>> #include "qemu/uuid.h"
>> #include "qemu/bswap.h"
>> +#include "qemu/xxhash.h"
>>
>> void qemu_uuid_generate(QemuUUID *uuid)
>> {
>> @@ -116,3 +117,40 @@ QemuUUID qemu_uuid_bswap(QemuUUID uuid)
>> bswap16s(&uuid.fields.time_high_and_version);
>> return uuid;
>> }
>> +
>> +uint32_t qemu_uuid_hash(const void *uuid)
>> +{
>> + QemuUUID *id = (QemuUUID *) uuid;
>> + uint64_t ab = (id->fields.time_low) |
>> + (((uint64_t) id->fields.time_mid) << 32) |
>> + (((uint64_t) id->fields.time_high_and_version) << 48);
>> + uint64_t cd = (id->fields.clock_seq_and_reserved) |
>> + (id->fields.clock_seq_low << 8);
>> + int i = 0, shift = 8;
>> +
>> + for (; i < 6; i++) {
>> + shift += 8;
>> + cd |= ((uint64_t) id->fields.node[i]) << shift;
>> + }
>> +
>> + return qemu_xxhash4(ab, cd);
>> +
>>
>
> That looks quite complex, and I have no idea if this is a good hash or not.
>
> Instead I would implement the traditional "djb" hash over the char[16]
> data (see g_str_hash implementation for \0-terminated implementation)
>
ok, I'll try to do something like that. Thanks for the suggestion.
I looked for any hash library within qemu code and xxhash was one of the
options that seemed easier to use.
>
>
>> }
>> +
>> +int qemu_uuid_equal(const void *lhv, const void *rhv)
>> +{
>> + int i;
>> + QemuUUID *lid = (QemuUUID *) lhv;
>> + QemuUUID *rid = (QemuUUID *) rhv;
>> + if (lid == NULL || rid == NULL) {
>> + return 0;
>> + }
>> + if (lid == rid) {
>> + return 1;
>> + }
>> + for (i = 0; i < 16; i++) {
>> + if (lid->data[i] != rid->data[i]) {
>> + return 0;
>> + }
>> + }
>> + return 1;
>> +}
>> --
>> 2.40.0
>>
>>
>
> --
> Marc-André Lureau
>
