Re: [Qemu-devel] [PATCH V9 6/8] qcow2: rollback on fail in qcow2_snapshot_create()

[Wenchao Xia]

于 2014/1/12 7:50, Max Reitz 写道:

On 05.01.2014 20:43, Wenchao Xia wrote:

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 <xiaw...@linux.vnet.ibm.com>
---
  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 5cac714..29ba534 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,
+                    "In rollback failed to restore refcount in
snapshot");

"Failed to restore the snapshot's refcount during rollback"? Or maybe
you could just leave the "snapshot" out, like "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,
+                     "In rollback failed to free L1 table: %s\n",

"Failed to free the L1 table in/during rollback"?

+                     strerror(-ret));
+    }
+
  fail:
      g_free(sn->id_str);
      g_free(sn->name);

Aside from these:

Reviewed-by: Max Reitz <mre...@redhat.com>

  I'll rework the commit and error message, thanks for review. :)