On 01/12/2015 20:39, Bart Van Assche wrote:
On 12/01/2015 10:35 AM, Sagi Grimberg wrote:
After dma_map_sg() has been called the return value of that function
must be used as the number of elements in the scatterlist instead of
scsi_sg_count().
Umm, but ib_map_mr_sg iterates on the sg list. Say you have sg_nents=3
and after mapping you got dma_nents=2 (2 entries are contig) and you
pass that, ib_sg_to_pages will only iterate on 2 elements won't it? am
I missing something?
Hello Sagi,
From https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt:
<quote>
With scatterlists, you map a region gathered from several regions by:
int i, count = dma_map_sg(dev, sglist, nents, direction);
struct scatterlist *sg;
for_each_sg(sglist, sg, count, i) {
hw_address[i] = sg_dma_address(sg);
hw_len[i] = sg_dma_len(sg);
}
where nents is the number of entries in the sglist.
</quote>
From Documentation/DMA_API.txt
<quote>
int
dma_map_sg(struct device *dev, struct scatterlist *sg,
int nents, enum dma_data_direction direction)
Returns: the number of DMA address segments mapped (this may be shorter
than <nents> passed in if some elements of the scatter/gather list are
physically or virtually adjacent and an IOMMU maps them with a single
entry).
</quote>
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