[Qemu-devel] [PATCH V10 6/8] qcow2: rollback on fail in qcow2_snapshot_create()

[Wenchao Xia]

A new variable *err_rollback is added to detect sub function's
rollback failure. If one step in rollback procedure fails, following
steps will be skipped, and the error message will be appended
to errp.

Signed-off-by: Wenchao Xia <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
---
 block/qcow2-snapshot.c |   37 ++++++++++++++++++++++++++++++++-----
 1 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index ee8f990..12938a0 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -423,6 +423,7 @@ void qcow2_snapshot_create(BlockDriverState *bs,
     int i, ret;
     uint64_t *l1_table = NULL;
     int64_t l1_table_offset;
+    Error *err_rollback = NULL;
 
     memset(sn, 0, sizeof(*sn));
 
@@ -471,7 +472,7 @@ void qcow2_snapshot_create(BlockDriverState *bs,
                          PRIu64 " with size %" PRIu64,
                          sn->l1_table_offset,
                          (uint64_t)(s->l1_size * sizeof(uint64_t)));
-        goto fail;
+        goto dealloc_l1_table;
     }
 
     ret = bdrv_pwrite(bs->file, sn->l1_table_offset, l1_table,
@@ -482,7 +483,7 @@ void qcow2_snapshot_create(BlockDriverState *bs,
                          PRIu64 " with size %" PRIu64,
                          sn->l1_table_offset,
                          (uint64_t)(s->l1_size * sizeof(uint64_t)));
-        goto fail;
+        goto dealloc_l1_table;
     }
 
     g_free(l1_table);
@@ -499,7 +500,7 @@ void qcow2_snapshot_create(BlockDriverState *bs,
                          "Failed in update of refcount for snapshot at %"
                          PRIu64 " with size %d",
                          s->l1_table_offset, s->l1_size);
-        goto fail;
+        goto dealloc_l1_table;
     }
 
     /* Append the new snapshot to the snapshot list */
@@ -512,12 +513,18 @@ void qcow2_snapshot_create(BlockDriverState *bs,
     s->snapshots = new_snapshot_list;
     s->snapshots[s->nb_snapshots++] = *sn;
 
-    ret = qcow2_write_snapshots(bs, errp, NULL);
+    ret = qcow2_write_snapshots(bs, errp, &err_rollback);
     if (ret < 0) {
         g_free(s->snapshots);
         s->snapshots = old_snapshot_list;
         s->nb_snapshots--;
-        goto fail;
+        if (error_is_set(&err_rollback)) {
+            error_append(errp, "%s", error_get_pretty(err_rollback));
+            error_free(err_rollback);
+            goto fail;
+        } else {
+            goto restore_refcount;
+        }
     }
 
     g_free(old_snapshot_list);
@@ -537,6 +544,26 @@ void qcow2_snapshot_create(BlockDriverState *bs,
 #endif
     return;
 
+restore_refcount:
+    if (qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size, -1)
+        < 0) {
+        /* Nothing can be done now, need image check later, skip following
+           rollback action. */
+        error_append(errp,
+                    "Failed to restore refcounts during rollback");
+        goto fail;
+    }
+
+dealloc_l1_table:
+    ret = qcow2_free_clusters(bs, sn->l1_table_offset,
+                              sn->l1_size * sizeof(uint64_t),
+                              QCOW2_DISCARD_ALWAYS);
+    if (ret < 0) {
+        error_append(errp,
+                     "Failed to free the L1 table during rollback: %s",
+                     strerror(-ret));
+    }
+
 fail:
     g_free(sn->id_str);
     g_free(sn->name);
-- 
1.7.1