[PULL 06/22] block/quorum.c: stable children names

[Max Reitz]

From: Lukas Straub <lukasstraub2@web.de>

If we remove the child with the highest index from the quorum,
decrement s->next_child_index. This way we get stable children
names as long as we only remove the last child.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Fixes: https://bugs.launchpad.net/bugs/1881231
Reviewed-by: Zhang Chen <chen.zhang@intel.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: 
<5d5f930424c1c770754041aa8ad6421dc4e2b58e.1596536719.git.lukasstraub2@web.de>
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/quorum.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/block/quorum.c b/block/quorum.c
index 6df9449fc2..e846a7e892 100644
--- a/block/quorum.c
+++ b/block/quorum.c
@@ -29,6 +29,8 @@
 
 #define HASH_LENGTH 32
 
+#define INDEXSTR_LEN 32
+
 #define QUORUM_OPT_VOTE_THRESHOLD "vote-threshold"
 #define QUORUM_OPT_BLKVERIFY      "blkverify"
 #define QUORUM_OPT_REWRITE        "rewrite-corrupted"
@@ -970,9 +972,9 @@ static int quorum_open(BlockDriverState *bs, QDict 
*options, int flags,
     opened = g_new0(bool, s->num_children);
 
     for (i = 0; i < s->num_children; i++) {
-        char indexstr[32];
-        ret = snprintf(indexstr, 32, "children.%d", i);
-        assert(ret < 32);
+        char indexstr[INDEXSTR_LEN];
+        ret = snprintf(indexstr, INDEXSTR_LEN, "children.%d", i);
+        assert(ret < INDEXSTR_LEN);
 
         s->children[i] = bdrv_open_child(NULL, options, indexstr, bs,
                                          &child_of_bds, BDRV_CHILD_DATA, false,
@@ -1024,7 +1026,7 @@ static void quorum_add_child(BlockDriverState *bs, 
BlockDriverState *child_bs,
 {
     BDRVQuorumState *s = bs->opaque;
     BdrvChild *child;
-    char indexstr[32];
+    char indexstr[INDEXSTR_LEN];
     int ret;
 
     if (s->is_blkverify) {
@@ -1039,8 +1041,8 @@ static void quorum_add_child(BlockDriverState *bs, 
BlockDriverState *child_bs,
         return;
     }
 
-    ret = snprintf(indexstr, 32, "children.%u", s->next_child_index);
-    if (ret < 0 || ret >= 32) {
+    ret = snprintf(indexstr, INDEXSTR_LEN, "children.%u", s->next_child_index);
+    if (ret < 0 || ret >= INDEXSTR_LEN) {
         error_setg(errp, "cannot generate child name");
         return;
     }
@@ -1068,6 +1070,7 @@ static void quorum_del_child(BlockDriverState *bs, 
BdrvChild *child,
                              Error **errp)
 {
     BDRVQuorumState *s = bs->opaque;
+    char indexstr[INDEXSTR_LEN];
     int i;
 
     for (i = 0; i < s->num_children; i++) {
@@ -1089,6 +1092,11 @@ static void quorum_del_child(BlockDriverState *bs, 
BdrvChild *child,
     /* We know now that num_children > threshold, so blkverify must be false */
     assert(!s->is_blkverify);
 
+    snprintf(indexstr, INDEXSTR_LEN, "children.%u", s->next_child_index - 1);
+    if (!strncmp(child->name, indexstr, INDEXSTR_LEN)) {
+        s->next_child_index--;
+    }
+
     bdrv_drained_begin(bs);
 
     /* We can safely remove this child now */
-- 
2.26.2