block-copy: move detecting fleecing scheme to block-copy

We want to simplify initialization interface of copy-before-write
filter as we are going to make it public. So, let's detect fleecing
scheme exactly in block-copy code, to not pass this information through
extra levels.

Why not just set BDRV_REQ_SERIALISING unconditionally: because we are
going to implement new more efficient fleecing scheme which will not
rely on backing feature.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20210824083856.17408-7-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

block/backup.c

@@ -407,7 +407,6 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     int64_t len, target_len;
     BackupBlockJob *job = NULL;
     int64_t cluster_size;
-    BdrvRequestFlags write_flags;
     BlockDriverState *cbw = NULL;
     BlockCopyState *bcs = NULL;
 
@@ -504,26 +503,8 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         goto error;
     }
 
-    /*
-     * If source is in backing chain of target assume that target is going to be
-     * used for "image fleecing", i.e. it should represent a kind of snapshot of
-     * source at backup-start point in time. And target is going to be read by
-     * somebody (for example, used as NBD export) during backup job.
-     *
-     * In this case, we need to add BDRV_REQ_SERIALISING write flag to avoid
-     * intersection of backup writes and third party reads from target,
-     * otherwise reading from target we may occasionally read already updated by
-     * guest data.
-     *
-     * For more information see commit f8d59dfb40bb and test
-     * tests/qemu-iotests/222
-     */
-    write_flags = (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
-                  (compress ? BDRV_REQ_WRITE_COMPRESSED : 0),
-
     cbw = bdrv_cbw_append(bs, target, filter_node_name,
-                                        cluster_size, perf,
+                          cluster_size, perf, compress, &bcs, errp);
-                                        write_flags, &bcs, errp);
     if (!cbw) {
         goto error;
     }

block/block-copy.c

@@ -317,10 +317,11 @@ static uint32_t block_copy_max_transfer(BdrvChild *source, BdrvChild *target)
 
 BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
                                      int64_t cluster_size, bool use_copy_range,
-                                     BdrvRequestFlags write_flags, Error **errp)
+                                     bool compress, Error **errp)
 {
     BlockCopyState *s;
     BdrvDirtyBitmap *copy_bitmap;
+    bool is_fleecing;
 
     copy_bitmap = bdrv_create_dirty_bitmap(source->bs, cluster_size, NULL,
                                            errp);
@@ -329,6 +330,22 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
     }
     bdrv_disable_dirty_bitmap(copy_bitmap);
 
+    /*
+     * If source is in backing chain of target assume that target is going to be
+     * used for "image fleecing", i.e. it should represent a kind of snapshot of
+     * source at backup-start point in time. And target is going to be read by
+     * somebody (for example, used as NBD export) during backup job.
+     *
+     * In this case, we need to add BDRV_REQ_SERIALISING write flag to avoid
+     * intersection of backup writes and third party reads from target,
+     * otherwise reading from target we may occasionally read already updated by
+     * guest data.
+     *
+     * For more information see commit f8d59dfb40bb and test
+     * tests/qemu-iotests/222
+     */
+    is_fleecing = bdrv_chain_contains(target->bs, source->bs);
+
     s = g_new(BlockCopyState, 1);
     *s = (BlockCopyState) {
         .source = source,
@@ -336,7 +353,8 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
         .copy_bitmap = copy_bitmap,
         .cluster_size = cluster_size,
         .len = bdrv_dirty_bitmap_size(copy_bitmap),
-        .write_flags = write_flags,
+        .write_flags = (is_fleecing ? BDRV_REQ_SERIALISING : 0) |
+            (compress ? BDRV_REQ_WRITE_COMPRESSED : 0),
         .mem = shres_create(BLOCK_COPY_MAX_MEM),
         .max_transfer = QEMU_ALIGN_DOWN(
                                     block_copy_max_transfer(source, target),
@@ -351,7 +369,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
          * behalf).
          */
         s->method = COPY_READ_WRITE_CLUSTER;
-    } else if (write_flags & BDRV_REQ_WRITE_COMPRESSED) {
+    } else if (compress) {
         /* Compression supports only cluster-size writes and no copy-range. */
         s->method = COPY_READ_WRITE_CLUSTER;
     } else {

block/copy-before-write.c

@@ -171,7 +171,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
                                   const char *filter_node_name,
                                   uint64_t cluster_size,
                                   BackupPerf *perf,
-                                  BdrvRequestFlags write_flags,
+                                  bool compress,
                                   BlockCopyState **bcs,
                                   Error **errp)
 {
@@ -218,7 +218,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
     state->cluster_size = cluster_size;
     state->bcs = block_copy_state_new(top->backing, state->target,
                                       cluster_size, perf->use_copy_range,
-                                      write_flags, errp);
+                                      compress, errp);
     if (!state->bcs) {
         error_prepend(errp, "Cannot create block-copy-state: ");
         goto fail;

block/copy-before-write.h

@@ -34,7 +34,7 @@ BlockDriverState *bdrv_cbw_append(BlockDriverState *source,
                                   const char *filter_node_name,
                                   uint64_t cluster_size,
                                   BackupPerf *perf,
-                                  BdrvRequestFlags write_flags,
+                                  bool compress,
                                   BlockCopyState **bcs,
                                   Error **errp);
 void bdrv_cbw_drop(BlockDriverState *bs);

include/block/block-copy.h

@@ -26,8 +26,7 @@ typedef struct BlockCopyCallState BlockCopyCallState;
 
 BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
                                      int64_t cluster_size, bool use_copy_range,
-                                     BdrvRequestFlags write_flags,
+                                     bool compress, Error **errp);
-                                     Error **errp);
 
 void block_copy_set_progress_meter(BlockCopyState *s, ProgressMeter *pm);