linux-kernel - Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg

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Date:   Tue, 27 Apr 2021 16:31:57 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma()

On Thu, Apr 08, 2021 at 11:01:12AM -0600, Logan Gunthorpe wrote:
> +/*
> + * dma_maps_sg_attrs returns 0 on error and > 0 on success.
> + * It should never return a value < 0.
> + */

Also it is weird a function that can't return 0 is returning an int type

> +int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
> +		enum dma_data_direction dir, unsigned long attrs)
> +{
> +	int ents;
> +
> +	ents = __dma_map_sg_attrs(dev, sg, nents, dir, attrs);
>  	BUG_ON(ents < 0);

if (WARN_ON(ents < 0))
     return 0;

instead of bug on?

Also, I see only 8 users of this function. How about just fix them all
to support negative returns and use this as the p2p API instead of
adding new API?

Add the opposite logic flag, 'DMA_ATTRS_NO_ERROR' and pass it through
the other api entry callers that can't handle it?

Jason