On Sun, Jan 25, 2015 at 9:43 PM, Christoph Hellwig <hch@xxxxxx> wrote:
> On Fri, Jan 23, 2015 at 10:08:01PM +0800, Ming Lei wrote:
>> >
>> > for_each_sg(sgl, sg, sgl_nents, i) {
>> > - iov[i].iov_len = sg->length;
>> > - iov[i].iov_base = kmap(sg_page(sg)) + sg->offset;
>> > - }
>> > + bvec[i].bv_page = sg_page(sg);
>> > + bvec[i].bv_len = sg->length;
>> > + bvec[i].bv_offset = sg->offset;
>>
>> Sorry, I have one question: I understand one bvec should only cover
>> one page, but
>> one sg may cover lots of pages, so could ITER_BVEC handle that correctly?
>
> Each scatterlist entry only contains a single page, which is returned
I mean scatterlist does not guarantee that, and one sg entry often
contains lots of pages, which DMA/bus address is continuous.
> by sg_page(sg). The existing code already relies on it because it
> kmaps that page.
If the existing target code path can guarantee that one sg entry
only contains one page, it should be better to use bio_vec explicitly
instead of scatterlist.
Thanks,
Ming Lei
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
