util/uuid: add a hash function
Add hash function to uuid module using the djb2 hash algorithm. Add a couple simple unit tests for the hash function, checking collisions for similar UUIDs. Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Signed-off-by: Albert Esteve <aesteve@redhat.com> Message-Id: <20231002065706.94707-2-aesteve@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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@ -96,4 +96,6 @@ int qemu_uuid_parse(const char *str, QemuUUID *uuid);
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QemuUUID qemu_uuid_bswap(QemuUUID uuid);
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uint32_t qemu_uuid_hash(const void *uuid);
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#endif
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@ -171,6 +171,32 @@ static void test_uuid_unparse_strdup(void)
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}
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}
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static void test_uuid_hash(void)
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{
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QemuUUID uuid;
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int i;
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for (i = 0; i < 100; i++) {
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qemu_uuid_generate(&uuid);
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/* Obtain the UUID hash */
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uint32_t hash_a = qemu_uuid_hash(&uuid);
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int data_idx = g_random_int_range(0, 15);
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/* Change a single random byte of the UUID */
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if (uuid.data[data_idx] < 0xFF) {
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uuid.data[data_idx]++;
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} else {
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uuid.data[data_idx]--;
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}
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/* Obtain the UUID hash again */
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uint32_t hash_b = qemu_uuid_hash(&uuid);
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/*
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* Both hashes shall be different (avoid collision)
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* for any change in the UUID fields
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*/
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g_assert_cmpint(hash_a, !=, hash_b);
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}
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}
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int main(int argc, char **argv)
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{
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g_test_init(&argc, &argv, NULL);
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@ -179,6 +205,7 @@ int main(int argc, char **argv)
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g_test_add_func("/uuid/parse", test_uuid_parse);
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g_test_add_func("/uuid/unparse", test_uuid_unparse);
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g_test_add_func("/uuid/unparse_strdup", test_uuid_unparse_strdup);
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g_test_add_func("/uuid/hash", test_uuid_hash);
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return g_test_run();
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}
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14
util/uuid.c
14
util/uuid.c
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@ -116,3 +116,17 @@ QemuUUID qemu_uuid_bswap(QemuUUID uuid)
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bswap16s(&uuid.fields.time_high_and_version);
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return uuid;
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}
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/* djb2 hash algorithm */
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uint32_t qemu_uuid_hash(const void *uuid)
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{
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QemuUUID *qid = (QemuUUID *) uuid;
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uint32_t h = 5381;
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int i;
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for (i = 0; i < ARRAY_SIZE(qid->data); i++) {
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h = (h << 5) + h + qid->data[i];
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}
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return h;
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}
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