[v11,25/34] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2()

Commit Message

Alberto Garcia July 10, 2020, 4:13 p.m. UTC

The L2 bitmap needs to be updated after each write to indicate what
new subclusters are now allocated. This needs to happen even if the
cluster was already allocated and the L2 entry was otherwise valid.

In some cases however a write operation doesn't need change the L2
bitmap (because all affected subclusters were already allocated). This
is detected in calculate_l2_meta(), and qcow2_alloc_cluster_link_l2()
is never called in those cases.

Signed-off-by: Alberto Garcia <[e-mail]>
Reviewed-by: Eric Blake <[e-mail]>
Reviewed-by: Max Reitz <[e-mail]>
---
 block/qcow2-cluster.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Patch

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index ea025dc531..5bdbb65e7b 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1062,6 +1062,24 @@  int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
         assert((offset & L2E_OFFSET_MASK) == offset);
 
         set_l2_entry(s, l2_slice, l2_index + i, offset | QCOW_OFLAG_COPIED);
+
+        /* Update bitmap with the subclusters that were just written */
+        if (has_subclusters(s)) {
+            uint64_t l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index + i);
+            unsigned written_from = m->cow_start.offset;
+            unsigned written_to = m->cow_end.offset + m->cow_end.nb_bytes ?:
+                m->nb_clusters << s->cluster_bits;
+            int first_sc, last_sc;
+            /* Narrow written_from and written_to down to the current cluster */
+            written_from = MAX(written_from, i << s->cluster_bits);
+            written_to   = MIN(written_to, (i + 1) << s->cluster_bits);
+            assert(written_from < written_to);
+            first_sc = offset_to_sc_index(s, written_from);
+            last_sc  = offset_to_sc_index(s, written_to - 1);
+            l2_bitmap |= QCOW_OFLAG_SUB_ALLOC_RANGE(first_sc, last_sc + 1);
+            l2_bitmap &= ~QCOW_OFLAG_SUB_ZERO_RANGE(first_sc, last_sc + 1);
+            set_l2_bitmap(s, l2_slice, l2_index + i, l2_bitmap);
+        }
      }