Re: [Qemu-devel] [PATCH V4 2/6] qcow2: add error message in qcow2_write_snapshots()

[Wenchao Xia]

> On 14.10.2013 23:52, Wenchao Xia wrote:

The function still returns int since qcow2_snapshot_delete() will
return the number.

Signed-off-by: Wenchao Xia <xiaw...@linux.vnet.ibm.com>
---
  block/qcow2-snapshot.c |   48 ++++++++++++++++++++++++++++++++++++++++++------
  1 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index b373f9a..4bd494b 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -152,7 +152,7 @@ fail:
  }

  /* add at the end of the file a new list of snapshots */
-static int qcow2_write_snapshots(BlockDriverState *bs)
+static int qcow2_write_snapshots(BlockDriverState *bs, Error **errp)
  {
      BDRVQcowState *s = bs->opaque;
      QCowSnapshot *sn;
@@ -183,10 +183,18 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
      offset = snapshots_offset;
      if (offset < 0) {
          ret = offset;
+        error_setg(errp,
+                   "Failed in allocation of cluster for snapshot list: "
+                   "%d (%s)",
+                   ret, strerror(-ret));

Again, error_setg_errno() is your friend.

          goto fail;
      }
      ret = bdrv_flush(bs);
      if (ret < 0) {
+        error_setg(errp,
+                   "Failed in flush after snapshot list cluster allocation: "
+                   "%d (%s)",
+                   ret, strerror(-ret));
          goto fail;
      }

@@ -194,6 +202,10 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
       * must indeed be completely free */
      ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
      if (ret < 0) {
+        error_setg(errp,
+                   "Failed in overlap check for snapshot list cluster at %"
+                   PRIi64 " with size %d: %d (%s)",
+                   offset, snapshots_size, ret, strerror(-ret));
          goto fail;
      }

@@ -227,24 +239,40 @@ static int qcow2_write_snapshots(BlockDriverState *bs)

          ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
          if (ret < 0) {
+            error_setg(errp,
+                       "Failed in write of snapshot header at %"
+                       PRIi64 " with size %" PRIu64 ": %d (%s)",
+                       offset, sizeof(h), ret, strerror(-ret));

Again, on 32 bit systems, sizeof(size_t) is generally 4 and not 8 (you
may want to cast sizeof(h) to int and just use %d).

  Maybe caset as (int64_t)sizeof(h) to avoid possible incomplete value?

              goto fail;
          }
          offset += sizeof(h);

          ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
          if (ret < 0) {
+            error_setg(errp,
+                       "Failed in write of extra snapshot data at %"
+                       PRIi64 " with size %" PRIu64 ": %d (%s)",
+                       offset, sizeof(extra), ret, strerror(-ret));

Same here.

              goto fail;
          }
          offset += sizeof(extra);

          ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
          if (ret < 0) {
+            error_setg(errp,
+                       "Failed in write of snapshot id string at %"
+                       PRIi64 " with size %d: %d (%s)",
+                       offset, id_str_size, ret, strerror(-ret));
              goto fail;
          }
          offset += id_str_size;

          ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
          if (ret < 0) {
+            error_setg(errp,
+                       "Failed in write of snapshot name string at %"
+                       PRIi64 " with size %d: %d (%s)",
+                       offset, name_size, ret, strerror(-ret));
              goto fail;
          }
          offset += name_size;
@@ -256,6 +284,9 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
       */
      ret = bdrv_flush(bs);
      if (ret < 0) {
+        error_setg(errp,
+                   "Failed in flush after snapshot list update: %d (%s)",
+                   ret, strerror(-ret));
          goto fail;
      }

@@ -268,6 +299,11 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
      ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
                             &header_data, sizeof(header_data));
      if (ret < 0) {
+        error_setg(errp,
+                   "Failed in update of image header at %"
+                   PRIi64 " with size %" PRIu64 ":%d (%s)",
+                   offsetof(QCowHeader, nb_snapshots), sizeof(header_data),
+                   ret, strerror(-ret));

And here (also applies to offsetof(), which returns size_t as well).
Also, you forgot a space after the colon (although you should be using
error_setg_errno() anyway).

  Will use error_setg_errno().

Max

          goto fail;
      }

@@ -283,6 +319,9 @@ fail:
          qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
                              QCOW2_DISCARD_ALWAYS);
      }
+    if (errp) {
+        g_assert(error_is_set(errp));
+    }
      return ret;
  }

@@ -446,10 +485,8 @@ void qcow2_snapshot_create(BlockDriverState *bs,
      s->snapshots = new_snapshot_list;
      s->snapshots[s->nb_snapshots++] = *sn;

-    ret = qcow2_write_snapshots(bs);
+    ret = qcow2_write_snapshots(bs, errp);
      if (ret < 0) {
-        /* Following line will be replaced with more detailed error later */
-        error_setg(errp, "Failed in write of snapshot");
          g_free(s->snapshots);
          s->snapshots = old_snapshot_list;
          s->nb_snapshots--;
@@ -623,9 +660,8 @@ int qcow2_snapshot_delete(BlockDriverState *bs,
              s->snapshots + snapshot_index + 1,
              (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
      s->nb_snapshots--;
-    ret = qcow2_write_snapshots(bs);
+    ret = qcow2_write_snapshots(bs, errp);
      if (ret < 0) {
-        error_setg(errp, "Failed to remove snapshot from snapshot list");
          return ret;
      }