[v7,25/32] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2()

Commit Message

Alberto Garcia May 25, 2020, 6:08 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]>
---
 block/qcow2-cluster.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

Comments

Eric Blake May 27, 2020, 4:52 p.m. UTC | #1

On 5/25/20 1:08 PM, Alberto Garcia wrote:
> 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]>
> ---
>   block/qcow2-cluster.c | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
> 

Reviewed-by: Eric Blake <[e-mail]>

Patch

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index edfc8ea91c..2276cee6d6 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1061,6 +1061,24 @@  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);
+        }
      }