nbd: Refactor counting of metadata contexts

Rather than open-code the count of negotiated contexts at several
sites, embed it directly into the struct.  This will make it easier
for upcoming commits to support even more simultaneous contexts.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20201027050556.269064-7-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

1 files changed, 15 insertions, 11 deletions

diff --git a/nbd/server.c b/nbd/server.c
index 77fdecd..42d494b 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -104,8 +104,7 @@ static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
  * NBD_OPT_LIST_META_CONTEXT. */
 typedef struct NBDExportMetaContexts {
     NBDExport *exp;
-    bool valid; /* means that negotiation of the option finished without
-                   errors */
+    size_t count; /* number of negotiated contexts */
     bool base_allocation; /* export base:allocation context (block status) */
     bool bitmap; /* export qemu:dirty-bitmap:<export bitmap name> */
 } NBDExportMetaContexts;
@@ -445,7 +444,9 @@ static int nbd_negotiate_handle_list(NBDClient *client, Error **errp)
 
 static void nbd_check_meta_export(NBDClient *client)
 {
-    client->export_meta.valid &= client->exp == client->export_meta.exp;
+    if (client->exp != client->export_meta.exp) {
+        client->export_meta.count = 0;
+    }
 }
 
 /* Send a reply to NBD_OPT_EXPORT_NAME.
@@ -945,6 +946,7 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
     NBDExportMetaContexts local_meta;
     uint32_t nb_queries;
     int i;
+    size_t count = 0;
 
     if (!client->structured_reply) {
         return nbd_opt_invalid(client, errp,
@@ -1001,6 +1003,7 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
         if (ret < 0) {
             return ret;
         }
+        count++;
     }
 
     if (meta->bitmap) {
@@ -1014,11 +1017,12 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
         if (ret < 0) {
             return ret;
         }
+        count++;
     }
 
     ret = nbd_negotiate_send_rep(client, NBD_REP_ACK, errp);
     if (ret == 0) {
-        meta->valid = true;
+        meta->count = count;
     }
 
     return ret;
@@ -2337,18 +2341,16 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
             return nbd_send_generic_reply(client, request->handle, -EINVAL,
                                           "need non-zero length", errp);
         }
-        if (client->export_meta.valid &&
-            (client->export_meta.base_allocation ||
-             client->export_meta.bitmap))
-        {
+        if (client->export_meta.count) {
             bool dont_fragment = request->flags & NBD_CMD_FLAG_REQ_ONE;
+            int contexts_remaining = client->export_meta.count;
 
             if (client->export_meta.base_allocation) {
                 ret = nbd_co_send_block_status(client, request->handle,
                                                blk_bs(exp->common.blk),
                                                request->from,
                                                request->len, dont_fragment,
-                                               !client->export_meta.bitmap,
+                                               !--contexts_remaining,
                                                NBD_META_ID_BASE_ALLOCATION,
                                                errp);
                 if (ret < 0) {
@@ -2360,13 +2362,15 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
                 ret = nbd_co_send_bitmap(client, request->handle,
                                          client->exp->export_bitmap,
                                          request->from, request->len,
-                                         dont_fragment,
-                                         true, NBD_META_ID_DIRTY_BITMAP, errp);
+                                         dont_fragment, !--contexts_remaining,
+                                         NBD_META_ID_DIRTY_BITMAP, errp);
                 if (ret < 0) {
                     return ret;
                 }
             }
 
+            assert(!contexts_remaining);
+
             return 0;
         } else {
             return nbd_send_generic_reply(client, request->handle, -EINVAL,