static int coroutine_fn backup_do_cow(BlockDriverState *bs, int64_t sector_num, int nb_sectors, bool *error_is_read, bool is_write_notifier) { BackupBlockJob *job = (BackupBlockJob *)bs->job; CowRequest cow_request; struct iovec iov; QEMUIOVector bounce_qiov; void *bounce_buffer = NULL; int ret = 0; int64_t sectors_per_cluster = cluster_size_sectors(job); int64_t start, end; int n; qemu_co_rwlock_rdlock(&job->flush_rwlock); start = sector_num / sectors_per_cluster; end = DIV_ROUND_UP(sector_num + nb_sectors, sectors_per_cluster); trace_backup_do_cow_enter(job, start, sector_num, nb_sectors); wait_for_overlapping_requests(job, start, end); cow_request_begin(&cow_request, job, start, end); for (; start < end; start++) { if (hbitmap_get(job->bitmap, start)) { trace_backup_do_cow_skip(job, start); continue; /* already copied */ } trace_backup_do_cow_process(job, start); n = MIN(sectors_per_cluster, job->common.len / BDRV_SECTOR_SIZE - start * sectors_per_cluster); if (!bounce_buffer) { bounce_buffer = qemu_blockalign(bs, job->cluster_size); } iov.iov_base = bounce_buffer; iov.iov_len = n * BDRV_SECTOR_SIZE; qemu_iovec_init_external(&bounce_qiov, &iov, 1); if (is_write_notifier) { ret = bdrv_co_readv_no_serialising(bs, start * sectors_per_cluster, n, &bounce_qiov); } else { ret = bdrv_co_readv(bs, start * sectors_per_cluster, n, &bounce_qiov); } if (ret < 0) { trace_backup_do_cow_read_fail(job, start, ret); if (error_is_read) { *error_is_read = true; } goto out; } if (buffer_is_zero(iov.iov_base, iov.iov_len)) { ret = bdrv_co_write_zeroes(job->target, start * sectors_per_cluster, n, BDRV_REQ_MAY_UNMAP); } else { ret = bdrv_co_writev(job->target, start * sectors_per_cluster, n, &bounce_qiov); } if (ret < 0) { trace_backup_do_cow_write_fail(job, start, ret); if (error_is_read) { *error_is_read = false; } goto out; } hbitmap_set(job->bitmap, start, 1); /* Publish progress, guest I/O counts as progress too. Note that the * offset field is an opaque progress value, it is not a disk offset. */ job->sectors_read += n; job->common.offset += n * BDRV_SECTOR_SIZE; } out: if (bounce_buffer) { qemu_vfree(bounce_buffer); } cow_request_end(&cow_request); trace_backup_do_cow_return(job, sector_num, nb_sectors, ret); qemu_co_rwlock_unlock(&job->flush_rwlock); return ret; }