nbd/server: Refactor list of negotiated meta contexts

Peform several minor refactorings of how the list of negotiated meta
contexts is managed, to make upcoming patches easier: Promote the
internal type NBDExportMetaContexts to the public opaque type
NBDMetaContexts, and mark exp const.  Use a shorter member name in
NBDClient.  Hoist calls to nbd_check_meta_context() earlier in their
callers, as the number of negotiated contexts may impact the flags
exposed in regards to an export, which in turn requires a new
parameter.  Drop a redundant parameter to nbd_negotiate_meta_queries.
No semantic change intended on the success path; on the failure path,
dropping context in nbd_check_meta_export even when reporting an error
is safer.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-ID: <20230925192229.3186470-24-eblake@redhat.com>

2 files changed, 31 insertions, 25 deletions

diff --git a/include/block/nbd.h b/include/block/nbd.h
index ba8724f533..2006497f98 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -29,6 +29,7 @@
 typedef struct NBDExport NBDExport;
 typedef struct NBDClient NBDClient;
 typedef struct NBDClientConnection NBDClientConnection;
+typedef struct NBDMetaContexts NBDMetaContexts;
 
 extern const BlockExportDriver blk_exp_nbd;
 
diff --git a/nbd/server.c b/nbd/server.c
index d3eed6535b..2719992db7 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -105,11 +105,13 @@ struct NBDExport {
 
 static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
 
-/* NBDExportMetaContexts represents a list of contexts to be exported,
+/*
+ * NBDMetaContexts represents a list of meta contexts in use,
  * as selected by NBD_OPT_SET_META_CONTEXT. Also used for
- * NBD_OPT_LIST_META_CONTEXT. */
-typedef struct NBDExportMetaContexts {
-    NBDExport *exp;
+ * NBD_OPT_LIST_META_CONTEXT.
+ */
+struct NBDMetaContexts {
+    const NBDExport *exp; /* associated export */
     size_t count; /* number of negotiated contexts */
     bool base_allocation; /* export base:allocation context (block status) */
     bool allocation_depth; /* export qemu:allocation-depth */
@@ -117,7 +119,7 @@ typedef struct NBDExportMetaContexts {
                     * export qemu:dirty-bitmap:<export bitmap name>,
                     * sized by exp->nr_export_bitmaps
                     */
-} NBDExportMetaContexts;
+};
 
 struct NBDClient {
     int refcount;
@@ -144,7 +146,7 @@ struct NBDClient {
     uint32_t check_align; /* If non-zero, check for aligned client requests */
 
     NBDMode mode;
-    NBDExportMetaContexts export_meta;
+    NBDMetaContexts contexts; /* Negotiated meta contexts */
 
     uint32_t opt; /* Current option being negotiated */
     uint32_t optlen; /* remaining length of data in ioc for the option being
@@ -455,10 +457,10 @@ static int nbd_negotiate_handle_list(NBDClient *client, Error **errp)
     return nbd_negotiate_send_rep(client, NBD_REP_ACK, errp);
 }
 
-static void nbd_check_meta_export(NBDClient *client)
+static void nbd_check_meta_export(NBDClient *client, NBDExport *exp)
 {
-    if (client->exp != client->export_meta.exp) {
-        client->export_meta.count = 0;
+    if (exp != client->contexts.exp) {
+        client->contexts.count = 0;
     }
 }
 
@@ -504,6 +506,7 @@ static int nbd_negotiate_handle_export_name(NBDClient *client, bool no_zeroes,
         error_setg(errp, "export not found");
         return -EINVAL;
     }
+    nbd_check_meta_export(client, client->exp);
 
     myflags = client->exp->nbdflags;
     if (client->mode >= NBD_MODE_STRUCTURED) {
@@ -521,7 +524,6 @@ static int nbd_negotiate_handle_export_name(NBDClient *client, bool no_zeroes,
 
     QTAILQ_INSERT_TAIL(&client->exp->clients, client, next);
     blk_exp_ref(&client->exp->common);
-    nbd_check_meta_export(client);
 
     return 0;
 }
@@ -641,6 +643,9 @@ static int nbd_negotiate_handle_info(NBDClient *client, Error **errp)
                                           errp, "export '%s' not present",
                                           sane_name);
     }
+    if (client->opt == NBD_OPT_GO) {
+        nbd_check_meta_export(client, exp);
+    }
 
     /* Don't bother sending NBD_INFO_NAME unless client requested it */
     if (sendname) {
@@ -729,7 +734,6 @@ static int nbd_negotiate_handle_info(NBDClient *client, Error **errp)
         client->check_align = check_align;
         QTAILQ_INSERT_TAIL(&client->exp->clients, client, next);
         blk_exp_ref(&client->exp->common);
-        nbd_check_meta_export(client);
         rc = 1;
     }
     return rc;
@@ -852,7 +856,7 @@ static bool nbd_strshift(const char **str, const char *prefix)
  * Handle queries to 'base' namespace. For now, only the base:allocation
  * context is available.  Return true if @query has been handled.
  */
-static bool nbd_meta_base_query(NBDClient *client, NBDExportMetaContexts *meta,
+static bool nbd_meta_base_query(NBDClient *client, NBDMetaContexts *meta,
                                 const char *query)
 {
     if (!nbd_strshift(&query, "base:")) {
@@ -872,7 +876,7 @@ static bool nbd_meta_base_query(NBDClient *client, NBDExportMetaContexts *meta,
  * and qemu:allocation-depth contexts are available.  Return true if @query
  * has been handled.
  */
-static bool nbd_meta_qemu_query(NBDClient *client, NBDExportMetaContexts *meta,
+static bool nbd_meta_qemu_query(NBDClient *client, NBDMetaContexts *meta,
                                 const char *query)
 {
     size_t i;
@@ -938,7 +942,7 @@ static bool nbd_meta_qemu_query(NBDClient *client, NBDExportMetaContexts *meta,
  * Return -errno on I/O error, 0 if option was completely handled by
  * sending a reply about inconsistent lengths, or 1 on success. */
 static int nbd_negotiate_meta_query(NBDClient *client,
-                                    NBDExportMetaContexts *meta, Error **errp)
+                                    NBDMetaContexts *meta, Error **errp)
 {
     int ret;
     g_autofree char *query = NULL;
@@ -977,14 +981,14 @@ static int nbd_negotiate_meta_query(NBDClient *client,
  * Handle NBD_OPT_LIST_META_CONTEXT and NBD_OPT_SET_META_CONTEXT
  *
  * Return -errno on I/O error, or 0 if option was completely handled. */
-static int nbd_negotiate_meta_queries(NBDClient *client,
-                                      NBDExportMetaContexts *meta, Error **errp)
+static int nbd_negotiate_meta_queries(NBDClient *client, Error **errp)
 {
     int ret;
     g_autofree char *export_name = NULL;
     /* Mark unused to work around https://bugs.llvm.org/show_bug.cgi?id=3888 */
     g_autofree G_GNUC_UNUSED bool *bitmaps = NULL;
-    NBDExportMetaContexts local_meta = {0};
+    NBDMetaContexts local_meta = {0};
+    NBDMetaContexts *meta;
     uint32_t nb_queries;
     size_t i;
     size_t count = 0;
@@ -1000,6 +1004,8 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
     if (client->opt == NBD_OPT_LIST_META_CONTEXT) {
         /* Only change the caller's meta on SET. */
         meta = &local_meta;
+    } else {
+        meta = &client->contexts;
     }
 
     g_free(meta->bitmaps);
@@ -1284,8 +1290,7 @@ static int nbd_negotiate_options(NBDClient *client, Error **errp)
 
             case NBD_OPT_LIST_META_CONTEXT:
             case NBD_OPT_SET_META_CONTEXT:
-                ret = nbd_negotiate_meta_queries(client, &client->export_meta,
-                                                 errp);
+                ret = nbd_negotiate_meta_queries(client, errp);
                 break;
 
             case NBD_OPT_EXTENDED_HEADERS:
@@ -1512,7 +1517,7 @@ void nbd_client_put(NBDClient *client)
             QTAILQ_REMOVE(&client->exp->clients, client, next);
             blk_exp_unref(&client->exp->common);
         }
-        g_free(client->export_meta.bitmaps);
+        g_free(client->contexts.bitmaps);
         g_free(client);
     }
 }
@@ -2749,11 +2754,11 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
         }
         assert(client->mode >= NBD_MODE_EXTENDED ||
                request->len <= UINT32_MAX);
-        if (client->export_meta.count) {
+        if (client->contexts.count) {
             bool dont_fragment = request->flags & NBD_CMD_FLAG_REQ_ONE;
-            int contexts_remaining = client->export_meta.count;
+            int contexts_remaining = client->contexts.count;
 
-            if (client->export_meta.base_allocation) {
+            if (client->contexts.base_allocation) {
                 ret = nbd_co_send_block_status(client, request,
                                                exp->common.blk,
                                                request->from,
@@ -2766,7 +2771,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
                 }
             }
 
-            if (client->export_meta.allocation_depth) {
+            if (client->contexts.allocation_depth) {
                 ret = nbd_co_send_block_status(client, request,
                                                exp->common.blk,
                                                request->from, request->len,
@@ -2780,7 +2785,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
             }
 
             for (i = 0; i < client->exp->nr_export_bitmaps; i++) {
-                if (!client->export_meta.bitmaps[i]) {
+                if (!client->contexts.bitmaps[i]) {
                     continue;
                 }
                 ret = nbd_co_send_bitmap(client, request,