[PATCH v3 4/6] nbd: Simplify qemu bitmap context name

[Eric Blake <eblake@redhat.com>]

Each dirty bitmap already knows its name; by reducing the scope of the
places where we construct "qemu:dirty-bitmap:NAME" strings, tracking
the name is more localized, and there are fewer per-export fields to
worry about.  This in turn will make it easier for an upcoming patch
to export more than one bitmap at once.

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 nbd/server.c | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index ea5de0b503cd..6326d6fe3f3a 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -97,7 +97,6 @@ struct NBDExport {

     bool alloc_context;
     BdrvDirtyBitmap *export_bitmap;
-    char *export_bitmap_context;
 };

 static QTAILQ_HEAD(, NBDExport) exports = QTAILQ_HEAD_INITIALIZER(exports);
@@ -882,14 +881,15 @@ static bool nbd_meta_qemu_query(NBDClient *client, NBDExportMetaContexts *meta,
     }

     if (nbd_strshift(&query, "dirty-bitmap:")) {
+        const char *bm_name;
+
         trace_nbd_negotiate_meta_query_parse("dirty-bitmap:");
         if (!meta->exp->export_bitmap) {
             trace_nbd_negotiate_meta_query_skip("no dirty-bitmap exported");
             return true;
         }
-        if (nbd_meta_empty_or_pattern(client,
-                                      meta->exp->export_bitmap_context +
-                                      strlen("qemu:dirty-bitmap:"), query)) {
+        bm_name = bdrv_dirty_bitmap_name(meta->exp->export_bitmap);
+        if (nbd_meta_empty_or_pattern(client, bm_name, query)) {
             meta->bitmap = true;
         }
         return true;
@@ -1025,8 +1025,11 @@ static int nbd_negotiate_meta_queries(NBDClient *client,
     }

     if (meta->bitmap) {
-        ret = nbd_negotiate_send_meta_context(client,
-                                              meta->exp->export_bitmap_context,
+        const char *bm_name = bdrv_dirty_bitmap_name(meta->exp->export_bitmap);
+        g_autofree char *context = g_strdup_printf("qemu:dirty-bitmap:%s",
+                                                   bm_name);
+
+        ret = nbd_negotiate_send_meta_context(client, context,
                                               NBD_META_ID_DIRTY_BITMAP,
                                               errp);
         if (ret < 0) {
@@ -1599,9 +1602,6 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
         bdrv_dirty_bitmap_set_busy(bm, true);
         exp->export_bitmap = bm;
         assert(strlen(bitmap) <= BDRV_BITMAP_MAX_NAME_SIZE);
-        exp->export_bitmap_context = g_strdup_printf("qemu:dirty-bitmap:%s",
-                                                     bitmap);
-        assert(strlen(exp->export_bitmap_context) < NBD_MAX_STRING_SIZE);
     }

     exp->alloc_context = arg->alloc;
@@ -1681,7 +1681,6 @@ static void nbd_export_delete(BlockExport *blk_exp)

     if (exp->export_bitmap) {
         bdrv_dirty_bitmap_set_busy(exp->export_bitmap, false);
-        g_free(exp->export_bitmap_context);
     }
 }

-- 
2.28.0