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[Qemu-devel] [PATCH V8 6/8] qcow2: rollback on fail in qcow2_snapshot_cr


From: Wenchao Xia
Subject: [Qemu-devel] [PATCH V8 6/8] qcow2: rollback on fail in qcow2_snapshot_create()
Date: Fri, 3 Jan 2014 11:08:50 +0800

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>
---
 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");
+        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",
+                     strerror(-ret));
+    }
+
 fail:
     g_free(sn->id_str);
     g_free(sn->name);
-- 
1.7.1




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