qcow2: Make qcow2_update_options() suitable for transactions

Before we can allow updating options at runtime with bdrv_reopen(), we
need to split the function into prepare/commit/abort parts.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>

block/qcow2.c

@@ -589,18 +589,25 @@ static void read_cache_sizes(BlockDriverState *bs, QemuOpts *opts,
     }
 }
 
-static int qcow2_update_options(BlockDriverState *bs, QDict *options,
-                                int flags, Error **errp)
+typedef struct Qcow2ReopenState {
+    Qcow2Cache *l2_table_cache;
+    Qcow2Cache *refcount_block_cache;
+    bool use_lazy_refcounts;
+    int overlap_check;
+    bool discard_passthrough[QCOW2_DISCARD_MAX];
+    uint64_t cache_clean_interval;
+} Qcow2ReopenState;
+
+static int qcow2_update_options_prepare(BlockDriverState *bs,
+                                        Qcow2ReopenState *r,
+                                        QDict *options, int flags,
+                                        Error **errp)
 {
     BDRVQcow2State *s = bs->opaque;
     QemuOpts *opts = NULL;
     const char *opt_overlap_check, *opt_overlap_check_template;
     int overlap_check_template = 0;
     uint64_t l2_cache_size, refcount_cache_size;
-    Qcow2Cache *l2_table_cache = NULL;
-    Qcow2Cache *refcount_block_cache = NULL;
-    uint64_t cache_clean_interval;
-    bool use_lazy_refcounts;
     int i;
     Error *local_err = NULL;
     int ret;
@@ -643,27 +650,27 @@ static int qcow2_update_options(BlockDriverState *bs, QDict *options,
     }
 
     /* alloc L2 table/refcount block cache */
-    l2_table_cache = qcow2_cache_create(bs, l2_cache_size);
-    refcount_block_cache = qcow2_cache_create(bs, refcount_cache_size);
-    if (l2_table_cache == NULL || refcount_block_cache == NULL) {
+    r->l2_table_cache = qcow2_cache_create(bs, l2_cache_size);
+    r->refcount_block_cache = qcow2_cache_create(bs, refcount_cache_size);
+    if (r->l2_table_cache == NULL || r->refcount_block_cache == NULL) {
         error_setg(errp, "Could not allocate metadata caches");
         ret = -ENOMEM;
         goto fail;
     }
 
     /* New interval for cache cleanup timer */
-    cache_clean_interval =
+    r->cache_clean_interval =
         qemu_opt_get_number(opts, QCOW2_OPT_CACHE_CLEAN_INTERVAL, 0);
-    if (cache_clean_interval > UINT_MAX) {
+    if (r->cache_clean_interval > UINT_MAX) {
         error_setg(errp, "Cache clean interval too big");
         ret = -EINVAL;
         goto fail;
     }
 
     /* Enable lazy_refcounts according to image and command line options */
-    use_lazy_refcounts = qemu_opt_get_bool(opts, QCOW2_OPT_LAZY_REFCOUNTS,
+    r->use_lazy_refcounts = qemu_opt_get_bool(opts, QCOW2_OPT_LAZY_REFCOUNTS,
         (s->compatible_features & QCOW2_COMPAT_LAZY_REFCOUNTS));
-    if (use_lazy_refcounts && s->qcow_version < 3) {
+    if (r->use_lazy_refcounts && s->qcow_version < 3) {
         error_setg(errp, "Lazy refcounts require a qcow2 image with at least "
                    "qemu 1.1 compatibility level");
         ret = -EINVAL;
@@ -702,49 +709,75 @@ static int qcow2_update_options(BlockDriverState *bs, QDict *options,
         goto fail;
     }
 
-    /*
-     * Start updating fields in BDRVQcow2State.
-     * After this point no failure is allowed any more.
-     */
-    s->overlap_check = 0;
+    r->overlap_check = 0;
     for (i = 0; i < QCOW2_OL_MAX_BITNR; i++) {
         /* overlap-check defines a template bitmask, but every flag may be
          * overwritten through the associated boolean option */
-        s->overlap_check |=
+        r->overlap_check |=
             qemu_opt_get_bool(opts, overlap_bool_option_names[i],
                               overlap_check_template & (1 << i)) << i;
     }
 
-    s->l2_table_cache = l2_table_cache;
-    s->refcount_block_cache = refcount_block_cache;
-
-    s->use_lazy_refcounts = use_lazy_refcounts;
-
-    s->discard_passthrough[QCOW2_DISCARD_NEVER] = false;
-    s->discard_passthrough[QCOW2_DISCARD_ALWAYS] = true;
-    s->discard_passthrough[QCOW2_DISCARD_REQUEST] =
+    r->discard_passthrough[QCOW2_DISCARD_NEVER] = false;
+    r->discard_passthrough[QCOW2_DISCARD_ALWAYS] = true;
+    r->discard_passthrough[QCOW2_DISCARD_REQUEST] =
         qemu_opt_get_bool(opts, QCOW2_OPT_DISCARD_REQUEST,
                           flags & BDRV_O_UNMAP);
-    s->discard_passthrough[QCOW2_DISCARD_SNAPSHOT] =
+    r->discard_passthrough[QCOW2_DISCARD_SNAPSHOT] =
         qemu_opt_get_bool(opts, QCOW2_OPT_DISCARD_SNAPSHOT, true);
-    s->discard_passthrough[QCOW2_DISCARD_OTHER] =
+    r->discard_passthrough[QCOW2_DISCARD_OTHER] =
         qemu_opt_get_bool(opts, QCOW2_OPT_DISCARD_OTHER, false);
 
-    s->cache_clean_interval = cache_clean_interval;
-    cache_clean_timer_init(bs, bdrv_get_aio_context(bs));
-
     ret = 0;
 fail:
-    if (ret < 0) {
-        if (l2_table_cache) {
-            qcow2_cache_destroy(bs, l2_table_cache);
+    qemu_opts_del(opts);
+    opts = NULL;
+    return ret;
+}
+
+static void qcow2_update_options_commit(BlockDriverState *bs,
+                                        Qcow2ReopenState *r)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int i;
+
+    s->l2_table_cache = r->l2_table_cache;
+    s->refcount_block_cache = r->refcount_block_cache;
+
+    s->overlap_check = r->overlap_check;
+    s->use_lazy_refcounts = r->use_lazy_refcounts;
+
+    for (i = 0; i < QCOW2_DISCARD_MAX; i++) {
+        s->discard_passthrough[i] = r->discard_passthrough[i];
     }
-        if (refcount_block_cache) {
-            qcow2_cache_destroy(bs, refcount_block_cache);
+
+    s->cache_clean_interval = r->cache_clean_interval;
+    cache_clean_timer_init(bs, bdrv_get_aio_context(bs));
+}
+
+static void qcow2_update_options_abort(BlockDriverState *bs,
+                                       Qcow2ReopenState *r)
+{
+    if (r->l2_table_cache) {
+        qcow2_cache_destroy(bs, r->l2_table_cache);
     }
+    if (r->refcount_block_cache) {
+        qcow2_cache_destroy(bs, r->refcount_block_cache);
+    }
+}
+
+static int qcow2_update_options(BlockDriverState *bs, QDict *options,
+                                int flags, Error **errp)
+{
+    Qcow2ReopenState r = {};
+    int ret;
+
+    ret = qcow2_update_options_prepare(bs, &r, options, flags, errp);
+    if (ret >= 0) {
+        qcow2_update_options_commit(bs, &r);
+    } else {
+        qcow2_update_options_abort(bs, &r);
     }
-    qemu_opts_del(opts);
-    opts = NULL;
 
     return ret;
 }