On Tue, Jun 28, 2022 at 12:26:10AM -0400, Kent Overstreet wrote: > On Mon, Jun 27, 2022 at 03:36:22PM +0800, Ming Lei wrote: > > Not mention bio_iter, bvec_iter has been 32 bytes, which is too big to > > hold in per-io data structure. With this patch, 8bytes is enough > > to rewind one bio if the end sector is fixed. > > And with rewind, you're making an assumption about the state the iterator is > going to be in when the IO has completed. > > What if the iterator was never advanced? bio_rewind() works as expected if the iterator doesn't advance, since bytes between the recorded position and the end position isn't changed, same with the end position. > > So say you check for that by saving some other part of the iterator - but that > may have legitimately changed too, if the bio was redirected (bi_sector changes) > or trimmed (bi_size changes) > > I still think this is an inherently buggy interface, the way it's being proposed > to be used. The patch did mention that the interface should be for situation in which end sector of bio won't change. Thanks, Ming
