On Thu, Mar 02, 2017 at 10:34:25AM +0800, Ming Lei wrote: > Hi Shaohua, > > On Wed, Mar 1, 2017 at 7:42 AM, Shaohua Li <s...@kernel.org> wrote: > > On Tue, Feb 28, 2017 at 11:41:39PM +0800, Ming Lei wrote: > >> Use this helper, instead of direct access to .bi_vcnt. > > > > what We really need to do for the behind IO is: > > - allocate memory and copy bio data to the memory > > - let behind bio do IO against the memory > > > > The behind bio doesn't need to have the exactly same bio_vec setting. If we > > just track the new memory, we don't need use the bio_segments_all and access > > bio_vec too. > > But we need to figure out how many vecs(each vec store one page) to be > allocated for the cloned/behind bio, and that is the only value of > bio_segments_all() here. Or you have idea to avoid that?
As I said, the behind bio doesn't need to have the exactly same bio_vec setting. We just allocate memory and copy original bio data to the memory, then do IO against the new memory. The behind bio segments == (bio->bi_iter.bi_size + PAGE_SIZE - 1) >> PAGE_SHIFT Thanks, Shaohua
