Re: [PATCH RFC 0/4] use scatter lists for all block pc requests and simplify hw handlers

Christoph Hellwig
2005-06-07T12:10:20Z

On Sat, Jun 04, 2005 at 11:07:14AM -0500, James Bottomley wrote:
> + if (bufflen)
> + req = blk_rq_map_kern(sreq->sr_device->request_queue,
> + sreq->sr_data_direction == DMA_TO_DEVICE,
> + buffer, bufflen, __GFP_WAIT);
> + else
> + req = blk_get_request(sreq->sr_device->request_queue, READ,
> + __GFP_WAIT);

shouldn't blk_rq_map_kern handle a 0 buffer and do nothing more than
blk_get_request? It's not exactly a criticial fastpath and that would make life
easier for the callers.

> + if (req->rq_disk) {
> + drv = *(struct scsi_driver **)req->rq_disk->private_data;
> + if (unlikely(!drv->init_command(cmd))) {
> + scsi_release_buffers(cmd);
> + scsi_put_command(cmd);
> + return BLKPREP_KILL;
> + }
> + } else {
> + memcpy(cmd->cmnd, req->cmd, sizeof(cmd->cmnd));
> + if (rq_data_dir(req) == WRITE)
> + cmd->sc_data_direction = DMA_TO_DEVICE;
> + else if (req->data_len)
> + cmd->sc_data_direction = DMA_FROM_DEVICE;
> + else
> + cmd->sc_data_direction = DMA_NONE;
> +
> + cmd->transfersize = req->data_len;
> + cmd->allowed = 3;
> + cmd->timeout_per_command = req->timeout;

most of this could probably be done in the midlayer always instead of the
upper drivers.