On 6/28/18 5:16 PM, Kent Overstreet wrote: > On Fri, Jun 29, 2018 at 07:10:47AM +0800, Ming Lei wrote: >> On Thu, Jun 28, 2018 at 11:21 PM, Bart Van Assche >> <bart.vanassche@xxxxxxx> wrote: >>> On 06/27/18 17:30, Ming Lei wrote: >>>> >>>> One core idea of immutable bvec is to use bio->bi_iter and the original >>>> bvec table to iterate over anywhere in the bio. That is why .bi_io_vec >>>> needs to copy, but not see any reason why .bi_vcnt needs to do. >>>> >>>> Do you have use cases on .bi_vcnt for cloned bio? >>> >>> >>> So far this is only a theoretical concern. There are many functions in the >>> block layer that use .bi_vcnt, and it is a lot of work to figure out all the >>> callers of all these functions. > > Back when I implemented immutable biovecs I thoroughly audited all the bi_vcnt > uses and removed all of them that weren't by the code that owns/submits the bio. > > Grepping around I see one or two suspicious uses.. blk-merge.c in particular > >> No, any functions using .bi_vcnt on a cloned-bio may be a bug, and we should >> take a close look. > > not just cloned bios, any code using bi_vcnt on a bio it didn't create is wrong. > > so big nack to this patch (I wasn't ccd on it though and it doesn't seem to have > hit lkml, so I can't find the original patch...) Yeah, you are both right, I was smoking crack. -- Jens Axboe
