On Wed, Apr 06, 2016 at 09:34:34AM +0800, Ming Lei wrote: > On Wed, Apr 6, 2016 at 8:18 AM, Kent Overstreet > <kent.overstreet@xxxxxxxxx> wrote: > > On Tue, Apr 05, 2016 at 07:56:46PM +0800, Ming Lei wrote: > >> Some drivers access bio->bi_vcnt and bio->bi_io_vec directly, > >> firstly it isn't a good practice, secondly it may cause trouble > >> for converting to multipage bvecs. > > > > "not good practice" is OO bullshit snake oil without more justification. We > > don't plaster accessors everywhere without an actual reason. > > > > How would it cause trouble with multipage bvecs? > > Simply speaking, the current drivers may depend on .bi_vcnt for > computing how many page there are in one bio. After multipage bvecs, > it is not true any more. Isn't it a actual reason? But it's completely valid to use bi_vcnt for segments, which is what it's always _really_ meant anyways. Sometimes you have cases where the meaning of a member changes significantly enough that you really don't want code using it accidentally anymore - like with Jens' patches that changed how bi_remaining and bi_cnt work, but after those patches it really wasn't correct to use those members directly anymore so he renamed them to prevent that. I don't buy that that's the case for multipage bvecs - the meaning of bi_vcnt itself isn't changing (it's just the number of entries in the array!) and it'll still be possible for code to correctly use it directly. Same with bio->bi_io_vec, it's still an array of biovecs, that's not changing. Your helpers are at the wrong level of abstraction. Also, there isn't a huge number of bi_vcnt references in the kernel anyways - the immutable biovec work required removing most of them. Instead of adding these low level accessors, it'd be better to convert code to higher level helpers (especially bio_add_page()) where applicable. -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
