block/backup: split shareable copying part from backup_do_cow

Split copying logic which will be shared with backup-top filter.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190920142056.12778-4-vsementsov@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/backup.c

@@ -248,26 +248,18 @@ static int64_t backup_bitmap_reset_unallocated(BackupBlockJob *s,
     return ret;
 }
 
-static int coroutine_fn backup_do_cow(BackupBlockJob *job,
-                                      int64_t offset, uint64_t bytes,
-                                      bool *error_is_read,
-                                      bool is_write_notifier)
+static int coroutine_fn backup_do_copy(BackupBlockJob *job,
+                                       int64_t start, uint64_t bytes,
+                                       bool *error_is_read,
+                                       bool is_write_notifier)
 {
-    CowRequest cow_request;
     int ret = 0;
-    int64_t start, end; /* bytes */
+    int64_t end = bytes + start; /* bytes */
     void *bounce_buffer = NULL;
     int64_t status_bytes;
 
-    qemu_co_rwlock_rdlock(&job->flush_rwlock);
-
-    start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
-    end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
-
-    trace_backup_do_cow_enter(job, start, offset, bytes);
-
-    wait_for_overlapping_requests(job, start, end);
-    cow_request_begin(&cow_request, job, start, end);
+    assert(QEMU_IS_ALIGNED(start, job->cluster_size));
+    assert(QEMU_IS_ALIGNED(end, job->cluster_size));
 
     while (start < end) {
         int64_t dirty_end;
@@ -326,6 +318,31 @@ static int coroutine_fn backup_do_cow(BackupBlockJob *job,
         qemu_vfree(bounce_buffer);
     }
 
+    return ret;
+}
+
+static int coroutine_fn backup_do_cow(BackupBlockJob *job,
+                                      int64_t offset, uint64_t bytes,
+                                      bool *error_is_read,
+                                      bool is_write_notifier)
+{
+    CowRequest cow_request;
+    int ret = 0;
+    int64_t start, end; /* bytes */
+
+    qemu_co_rwlock_rdlock(&job->flush_rwlock);
+
+    start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
+    end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
+
+    trace_backup_do_cow_enter(job, start, offset, bytes);
+
+    wait_for_overlapping_requests(job, start, end);
+    cow_request_begin(&cow_request, job, start, end);
+
+    ret = backup_do_copy(job, start, end - start, error_is_read,
+                         is_write_notifier);
+
     cow_request_end(&cow_request);
 
     trace_backup_do_cow_return(job, offset, bytes, ret);