[PATCH v2 04/10] qcow2-refcount: introduce fix_l2_entry_by_zero()

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Split fix_l2_entry_by_zero() out of check_refcounts_l2() to be
reused in further patch.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 block/qcow2-refcount.c | 87 +++++++++++++++++++++++++++++-------------
 1 file changed, 60 insertions(+), 27 deletions(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 66cbb94ef9..184b96ad63 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1587,6 +1587,54 @@ enum {
     CHECK_FRAG_INFO = 0x2,      /* update BlockFragInfo counters */
 };
 
+/*
+ * Fix L2 entry by making it QCOW2_CLUSTER_ZERO_PLAIN.
+ *
+ * This function decrements res->corruptions on success, so the caller is
+ * responsible to increment res->corruptions prior to the call.
+ *
+ * On failure in-memory @l2_table may be modified.
+ */
+static int fix_l2_entry_by_zero(BlockDriverState *bs, BdrvCheckResult *res,
+                                uint64_t l2_offset,
+                                uint64_t *l2_table, int l2_index, bool active,
+                                bool *metadata_overlap)
+{
+    BDRVQcow2State *s = bs->opaque;
+    int ret;
+    int idx = l2_index * (l2_entry_size(s) / sizeof(uint64_t));
+    uint64_t l2e_offset = l2_offset + (uint64_t)l2_index * l2_entry_size(s);
+    int ign = active ? QCOW2_OL_ACTIVE_L2 : QCOW2_OL_INACTIVE_L2;
+    uint64_t l2_entry = has_subclusters(s) ? 0 : QCOW_OFLAG_ZERO;
+
+    set_l2_entry(s, l2_table, l2_index, l2_entry);
+    ret = qcow2_pre_write_overlap_check(bs, ign, l2e_offset, l2_entry_size(s),
+                                        false);
+    if (metadata_overlap) {
+        *metadata_overlap = ret < 0;
+    }
+    if (ret < 0) {
+        fprintf(stderr, "ERROR: Overlap check failed\n");
+        goto fail;
+    }
+
+    ret = bdrv_pwrite_sync(bs->file, l2e_offset, &l2_table[idx],
+                           l2_entry_size(s));
+    if (ret < 0) {
+        fprintf(stderr, "ERROR: Failed to overwrite L2 "
+                "table entry: %s\n", strerror(-ret));
+        goto fail;
+    }
+
+    res->corruptions--;
+    res->corruptions_fixed++;
+    return 0;
+
+fail:
+    res->check_errors++;
+    return ret;
+}
+
 /*
  * Increases the refcount in the given refcount table for the all clusters
  * referenced in the L2 table. While doing so, performs some checks on L2
@@ -1606,6 +1654,7 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
     int i, ret;
     size_t l2_size_bytes = s->l2_size * l2_entry_size(s);
     g_autofree uint64_t *l2_table = g_malloc(l2_size_bytes);
+    bool metadata_overlap;
 
     /* Read L2 table from disk */
     ret = bdrv_pread(bs->file, l2_offset, l2_table, l2_size_bytes);
@@ -1685,19 +1734,10 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
                             fix & BDRV_FIX_ERRORS ? "Repairing" : "ERROR",
                             offset);
                     if (fix & BDRV_FIX_ERRORS) {
-                        int idx = i * (l2_entry_size(s) / sizeof(uint64_t));
-                        uint64_t l2e_offset =
-                            l2_offset + (uint64_t)i * l2_entry_size(s);
-                        int ign = active ? QCOW2_OL_ACTIVE_L2 :
-                                           QCOW2_OL_INACTIVE_L2;
-
-                        l2_entry = has_subclusters(s) ? 0 : QCOW_OFLAG_ZERO;
-                        set_l2_entry(s, l2_table, i, l2_entry);
-                        ret = qcow2_pre_write_overlap_check(bs, ign,
-                                l2e_offset, l2_entry_size(s), false);
-                        if (ret < 0) {
-                            fprintf(stderr, "ERROR: Overlap check failed\n");
-                            res->check_errors++;
+                        ret = fix_l2_entry_by_zero(bs, res, l2_offset,
+                                                   l2_table, i, active,
+                                                   &metadata_overlap);
+                        if (metadata_overlap) {
                             /*
                              * Something is seriously wrong, so abort checking
                              * this L2 table.
@@ -1705,26 +1745,19 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
                             return ret;
                         }
 
-                        ret = bdrv_pwrite_sync(bs->file, l2e_offset,
-                                               &l2_table[idx],
-                                               l2_entry_size(s));
-                        if (ret < 0) {
-                            fprintf(stderr, "ERROR: Failed to overwrite L2 "
-                                    "table entry: %s\n", strerror(-ret));
-                            res->check_errors++;
-                            /*
-                             * Do not abort, continue checking the rest of this
-                             * L2 table's entries.
-                             */
-                        } else {
-                            res->corruptions--;
-                            res->corruptions_fixed++;
+                        if (ret == 0) {
                             /*
                              * Skip marking the cluster as used
                              * (it is unused now).
                              */
                             continue;
                         }
+
+                        /*
+                         * Failed to fix.
+                         * Do not abort, continue checking the rest of this
+                         * L2 table's entries.
+                         */
                     }
                 } else {
                     fprintf(stderr, "ERROR offset=%" PRIx64 ": Data cluster is "
-- 
2.29.2