[Qemu-devel] [PATCH v2 1/1] quorum: Change vote rules for 64 bits hash

[Changlong Xie]

If quorum has two children(A, B). A do flush sucessfully, but B flush failed.
We MUST choice A as winner rather than just pick anyone of them. Otherwise
the filesystem of guest will become read-only with following errors:

end_request: I/O error, dev vda, sector 11159960
Aborting journal on device vda3-8
EXT4-fs error (device vda3): ext4_journal_start_sb:327: Detected abort journal
EXT4-fs (vda3): Remounting filesystem read-only

Signed-off-by: Wen Congyang <address@hidden>
Signed-off-by: Changlong Xie <address@hidden>
---
 block/quorum.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/block/quorum.c b/block/quorum.c
index 11cc60b..f094208 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -447,7 +447,8 @@ static int quorum_compute_hash(QuorumAIOCB *acb, int i, 
QuorumVoteValue *hash)
     return 0;
 }
 
-static QuorumVoteVersion *quorum_get_vote_winner(QuorumVotes *votes)
+static QuorumVoteVersion *quorum_get_vote_winner(QuorumVotes *votes,
+                                                 bool vote_error)
 {
     int max = 0;
     QuorumVoteVersion *candidate, *winner = NULL;
@@ -456,6 +457,12 @@ static QuorumVoteVersion 
*quorum_get_vote_winner(QuorumVotes *votes)
         if (candidate->vote_count > max) {
             max = candidate->vote_count;
             winner = candidate;
+            continue;
+        }
+        /* For 64 bit hash */
+        if (vote_error && candidate->vote_count == max
+            && candidate->value.l == 0) {
+            winner = candidate;
         }
     }
 
@@ -545,7 +552,7 @@ static int quorum_vote_error(QuorumAIOCB *acb)
     }
 
     if (error) {
-        winner = quorum_get_vote_winner(&error_votes);
+        winner = quorum_get_vote_winner(&error_votes, false);
         ret = winner->value.l;
     }
 
@@ -610,7 +617,7 @@ static bool quorum_vote(QuorumAIOCB *acb)
     }
 
     /* vote to select the most represented version */
-    winner = quorum_get_vote_winner(&acb->votes);
+    winner = quorum_get_vote_winner(&acb->votes, false);
 
     /* if the winner count is smaller than threshold the read fails */
     if (winner->vote_count < s->threshold) {
@@ -770,7 +777,7 @@ static coroutine_fn int quorum_co_flush(BlockDriverState 
*bs)
         quorum_count_vote(&error_votes, &result_value, i);
     }
 
-    winner = quorum_get_vote_winner(&error_votes);
+    winner = quorum_get_vote_winner(&error_votes, true);
     result = winner->value.l;
 
     quorum_free_vote_list(&error_votes);
-- 
1.9.3