[ovs-dev] [PATCH] dpif: Always generate RFC4122 UUIDs for UFID.

[Joe Stringer]

This patch sacrifices a few bits of hash quality from the 128-bit unique
flow identifiers to make the UFIDs RFC4122-conformant as per the version 4
(random) UUID spec. Given that the 128-bit space is already quite large,
this should not affect the spread of UFIDs in any meaningful way for
hashing.

Signed-off-by: Joe Stringer <joestringer at nicira.com>
---
This is independent of the recent series "odp-util: Reuse UUID
marshalling for UFID.", but may make more sense in the context of the
discussion on that patch.
---
 lib/dpif.c | 2 ++
 lib/uuid.c | 6 ++++++
 lib/uuid.h | 1 +
 3 files changed, 9 insertions(+)

diff --git a/lib/dpif.c b/lib/dpif.c
index b2f973c..783a715 100644
--- a/lib/dpif.c
+++ b/lib/dpif.c
@@ -46,6 +46,7 @@
 #include "tnl-arp-cache.h"
 #include "tnl-ports.h"
 #include "util.h"
+#include "uuid.h"
 #include "valgrind.h"
 #include "openvswitch/vlog.h"
 
@@ -852,6 +853,7 @@ dpif_flow_hash(const struct dpif *dpif OVS_UNUSED,
         ovsthread_once_done(&once);
     }
     hash_bytes128(key, key_len, secret, hash);
+    uuid_set_bits_v4((struct uuid *)hash);
 }
 
 /* Deletes all flows from 'dpif'.  Returns 0 if successful, otherwise a
diff --git a/lib/uuid.c b/lib/uuid.c
index df1206e..0f2a58e 100644
--- a/lib/uuid.c
+++ b/lib/uuid.c
@@ -98,6 +98,12 @@ uuid_generate(struct uuid *uuid)
     /* AES output is exactly 16 bytes, so we encrypt directly into 'uuid'. */
     aes128_encrypt(&key, copy, uuid);
 
+    uuid_set_bits_v4(uuid);
+}
+
+void
+uuid_set_bits_v4(struct uuid *uuid)
+{
     /* Set bits to indicate a random UUID.  See RFC 4122 section 4.4. */
     uuid->parts[2] &= ~0xc0000000;
     uuid->parts[2] |=  0x80000000;
diff --git a/lib/uuid.h b/lib/uuid.h
index 37e01d0..8c6f2f1 100644
--- a/lib/uuid.h
+++ b/lib/uuid.h
@@ -78,5 +78,6 @@ bool uuid_is_zero(const struct uuid *);
 int uuid_compare_3way(const struct uuid *, const struct uuid *);
 bool uuid_from_string(struct uuid *, const char *);
 bool uuid_from_string_prefix(struct uuid *, const char *);
+void uuid_set_bits_v4(struct uuid *);
 
 #endif /* uuid.h */
-- 
2.1.4