qcow2: Batch discards

This optimises the discard operation for freed clusters by batching
discard requests (both snapshot deletion and bdrv_discard end up
updating the refcounts cluster by cluster).

Note that we don't discard asynchronously, but keep s->lock held. This
is to avoid that a freed cluster is reallocated and written to while the
discard is still in flight.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/block/qcow2.h b/block/qcow2.h
index 6f91b9a016..3b2d5cda71 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -147,6 +147,13 @@ typedef struct Qcow2Feature {
     char    name[46];
 } QEMU_PACKED Qcow2Feature;
 
+typedef struct Qcow2DiscardRegion {
+    BlockDriverState *bs;
+    uint64_t offset;
+    uint64_t bytes;
+    QTAILQ_ENTRY(Qcow2DiscardRegion) next;
+} Qcow2DiscardRegion;
+
 typedef struct BDRVQcowState {
     int cluster_bits;
     int cluster_size;
@@ -199,6 +206,8 @@ typedef struct BDRVQcowState {
     size_t unknown_header_fields_size;
     void* unknown_header_fields;
     QLIST_HEAD(, Qcow2UnknownHeaderExtension) unknown_header_ext;
+    QTAILQ_HEAD (, Qcow2DiscardRegion) discards;
+    bool cache_discards;
 } BDRVQcowState;
 
 /* XXX: use std qcow open function ? */
@@ -374,6 +383,8 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
 int qcow2_check_refcounts(BlockDriverState *bs, BdrvCheckResult *res,
                           BdrvCheckMode fix);
 
+void qcow2_process_discards(BlockDriverState *bs, int ret);
+
 /* qcow2-cluster.c functions */
 int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
                         bool exact_size);