Re: [PATCH-v3 4/9] vhost/scsi: Add ANY_LAYOUT iov -> sgl mapping prerequisites

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Feb 03, 2015 at 06:29:58AM +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@linux-iscsi.org>
> 
> This patch adds ANY_LAYOUT prerequisites logic for accepting a set of
> protection + data payloads via iov_iter.  Also includes helpers for
> calcuating SGLs + invoking vhost_scsi_map_to_sgl() with a known number
> of iovecs.
> 
> Required by ANY_LAYOUT processing when struct iovec may be offset into
> the first outgoing virtio-scsi request header.
> 
> v2 changes:
>   - Clear ->tvc_sgl_count for vhost_scsi_mapal failure
>   - Make vhost_scsi_mapal + vhost_scsi_calc_sgls accept max_niov
>   - Minor cleanups
> 
> v3 changes:
>   - Update vhost_scsi_mapal + friends to use iov_iter
>   - Move iov_iter sanity checks into vhost_scsi_calc_sgls
>   - Convert vhost_scsi_calc_sgls() to iov_iter_npages()

I guess if this goes through your tree, you can drop these
when applying, but it's best not to assume this, and put
changelog after ---.

> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> ---
>  drivers/vhost/scsi.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 93 insertions(+)
> 
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index c3b12b3..7dfff15 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -914,6 +914,99 @@ vhost_scsi_map_iov_to_prot(struct tcm_vhost_cmd *cmd,
>  	return 0;
>  }
>  
> +static int
> +vhost_scsi_calc_sgls(struct iov_iter *iter, size_t bytes, int max_sgls)
> +{
> +	int sgl_count = 0;
> +
> +	if (!iter || !iter->iov) {
> +		pr_err("%s: iter->iov is NULL, but expected bytes: %zu"
> +		       " present\n", __func__, bytes);
> +		return -EINVAL;
> +	}
> +
> +	sgl_count = iov_iter_npages(iter, 0xffff);
> +	if (sgl_count > max_sgls) {
> +		pr_err("%s: requested sgl_count: %d exceeds pre-allocated"
> +		       " max_sgls: %d\n", __func__, sgl_count, max_sgls);
> +		return -EINVAL;
> +	}
> +	return sgl_count;
> +}
> +
> +static int
> +vhost_scsi_iov_to_sgl(struct tcm_vhost_cmd *cmd, bool write,
> +		      struct iov_iter *iter, struct scatterlist *sg,
> +		      int sg_count)
> +{
> +	size_t off = iter->iov_offset;
> +	int i, ret;
> +
> +	for (i = 0; i < iter->nr_segs; i++) {
> +		void __user *base = iter->iov[i].iov_base + off;
> +		size_t len = iter->iov[i].iov_len - off;
> +
> +		ret = vhost_scsi_map_to_sgl(cmd, base, len, sg, write);
> +		if (ret < 0) {
> +			for (i = 0; i < sg_count; i++) {
> +				struct page *page = sg_page(&sg[i]);
> +				if (page)
> +					put_page(page);
> +			}
> +			return ret;
> +		}
> +		sg += ret;
> +		off = 0;
> +	}
> +	return 0;
> +}
> +
> +static int
> +vhost_scsi_mapal(struct tcm_vhost_cmd *cmd,
> +		 size_t prot_bytes, struct iov_iter *prot_iter,
> +		 size_t data_bytes, struct iov_iter *data_iter)
> +{
> +	int sgl_count, ret;
> +	bool write = (cmd->tvc_data_direction == DMA_FROM_DEVICE);
> +
> +	if (prot_bytes) {
> +		sgl_count = vhost_scsi_calc_sgls(prot_iter, prot_bytes,
> +						 TCM_VHOST_PREALLOC_PROT_SGLS);
> +		if (sgl_count < 0)
> +			return sgl_count;
> +
> +		sg_init_table(cmd->tvc_prot_sgl, sgl_count);
> +		cmd->tvc_prot_sgl_count = sgl_count;
> +		pr_debug("%s prot_sg %p prot_sgl_count %u\n", __func__,
> +			 cmd->tvc_prot_sgl, cmd->tvc_prot_sgl_count);
> +
> +		ret = vhost_scsi_iov_to_sgl(cmd, write, prot_iter,
> +					    cmd->tvc_prot_sgl,
> +					    cmd->tvc_prot_sgl_count);
> +		if (ret < 0) {
> +			cmd->tvc_prot_sgl_count = 0;
> +			return ret;
> +		}
> +	}
> +	sgl_count = vhost_scsi_calc_sgls(data_iter, data_bytes,
> +					 TCM_VHOST_PREALLOC_SGLS);
> +	if (sgl_count < 0)
> +		return sgl_count;
> +
> +	sg_init_table(cmd->tvc_sgl, sgl_count);
> +	cmd->tvc_sgl_count = sgl_count;
> +	pr_debug("%s data_sg %p data_sgl_count %u\n", __func__,
> +		  cmd->tvc_sgl, cmd->tvc_sgl_count);
> +
> +	ret = vhost_scsi_iov_to_sgl(cmd, write, data_iter,
> +				    cmd->tvc_sgl, cmd->tvc_sgl_count);
> +	if (ret < 0) {
> +		cmd->tvc_sgl_count = 0;
> +		return ret;
> +	}
> +	return 0;
> +}
> +
>  static void tcm_vhost_submission_work(struct work_struct *work)
>  {
>  	struct tcm_vhost_cmd *cmd =
> -- 
> 1.9.1