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>

3 files changed, 43 insertions, 0 deletions

diff --git a/include/qemu/uuid.h b/include/qemu/uuid.h
index dc40ee1fc9..e24a1099e4 100644
--- a/include/qemu/uuid.h
+++ b/include/qemu/uuid.h
@@ -96,4 +96,6 @@ int qemu_uuid_parse(const char *str, QemuUUID *uuid);
 
 QemuUUID qemu_uuid_bswap(QemuUUID uuid);
 
+uint32_t qemu_uuid_hash(const void *uuid);
+
 #endif
diff --git a/tests/unit/test-uuid.c b/tests/unit/test-uuid.c
index c111de5fc1..aedc125ae9 100644
--- a/tests/unit/test-uuid.c
+++ b/tests/unit/test-uuid.c
@@ -171,6 +171,32 @@ 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);
+    }
+}
+
 int main(int argc, char **argv)
 {
     g_test_init(&argc, &argv, NULL);
@@ -179,6 +205,7 @@ 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);
 
     return g_test_run();
 }
diff --git a/util/uuid.c b/util/uuid.c
index b1108dde78..d71aa79e5e 100644
--- a/util/uuid.c
+++ b/util/uuid.c
@@ -116,3 +116,17 @@ QemuUUID qemu_uuid_bswap(QemuUUID uuid)
     bswap16s(&uuid.fields.time_high_and_version);
     return uuid;
 }
+
+/* djb2 hash algorithm */
+uint32_t qemu_uuid_hash(const void *uuid)
+{
+    QemuUUID *qid = (QemuUUID *) uuid;
+    uint32_t h = 5381;
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(qid->data); i++) {
+        h = (h << 5) + h + qid->data[i];
+    }
+
+    return h;
+}