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Re: [Qemu-devel] [PATCH v6 09/11] qcow2: Clean up after refcount rebuild


From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH v6 09/11] qcow2: Clean up after refcount rebuild
Date: Tue, 21 Oct 2014 12:16:14 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

On 2014-10-21 at 11:59, Kevin Wolf wrote:
Am 20.10.2014 um 16:35 hat Max Reitz geschrieben:
Because the old refcount structure will be leaked after having rebuilt
it, we need to recalculate the refcounts and run a leak-fixing operation
afterwards (if leaks should be fixed at all).

Signed-off-by: Max Reitz <address@hidden>
Reviewed-by: BenoƮt Canet <address@hidden>
---
  block/qcow2-refcount.c | 35 +++++++++++++++++++++++++++++++++++
  1 file changed, 35 insertions(+)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 75e726b..3730be2 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1956,12 +1956,47 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
                        nb_clusters);
if (rebuild && (fix & BDRV_FIX_ERRORS)) {
+        BdrvCheckResult old_res = *res;
+
          fprintf(stderr, "Rebuilding refcount structure\n");
          ret = rebuild_refcount_structure(bs, res, &refcount_table,
                                           &nb_clusters);
          if (ret < 0) {
              goto fail;
          }
+
+        res->corruptions = 0;
+        res->leaks = 0;
+
+        /* Because the old reftable has been exchanged for a new one the
+         * references have to be recalculated */
+        rebuild = false;
+        memset(refcount_table, 0, nb_clusters * sizeof(uint16_t));
+        ret = calculate_refcounts(bs, res, 0, &rebuild, &refcount_table,
+                                  &nb_clusters);
+        if (ret < 0) {
+            goto fail;
+        }
+
+        if (fix & BDRV_FIX_LEAKS) {
+            /* The old refcount structures are now leaked, fix it; the result
+             * can be ignored */
+            pre_compare_res = *res;
I would prefer using another local variable here. At the first sight
it's not quite clear which references to pre_compare_res correspond to
which state.

Why not.

+            compare_refcounts(bs, res, BDRV_FIX_LEAKS, &rebuild,
+                              &highest_cluster, refcount_table, nb_clusters);
+            if (rebuild) {
+                fprintf(stderr, "ERROR rebuilt refcount structure is still "
+                        "broken\n");
+            }
+            *res = pre_compare_res;
+        }
+
+        if (res->corruptions < old_res.corruptions) {
+            res->corruptions_fixed += old_res.corruptions - res->corruptions;
+        }
+        if (res->leaks < old_res.leaks) {
+            res->leaks_fixed += old_res.leaks - res->leaks;
+        }
For these numbers to be accurate, don't we need to run
compare_refcounts() unconditionally and only make BDRV_FIX_LEAKS
conditional?

Actually, there is no difference, because at the point of this patch, you cannot use BDRV_FIX_ERRORS without BDRV_FIX_LEAKS. But it'd be more correct, right.

Thanks,

Max

Now that I've read the rest of the series, comparing res and old_res
actually makes sense, so maybe it's not necessary to introduce a
Qcow2CheckResult.

      } else if (fix) {
          if (rebuild) {
              fprintf(stderr, "ERROR need to rebuild refcount structures\n");
--
2.1.2
Kevin




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