Re: [Drbd-dev] [fix] drbd uses wrong API for struct bio

[Jens Axboe <axboe@suse.de>]

On Tue, Jan 25 2005, Philipp Reisner wrote:
> Am Dienstag, 25. Januar 2005 00:23 schrieb Lars Marowsky-Bree:
> > On 2005-01-23T17:16:33, Lars Marowsky-Bree <lmb@suse.de> wrote:
> >
> > The attached patch fixes drbds useage of bios up some. The proper fix
> > would be to indeed change it over to use bio_alloc(), bio_get/put(),
> > bio_add_page(), bio_clone (instead of __bio_clone) et cetera, but that
> > fix is too complex for the timeframe I have right now.
> >
> > This should keep drbd-0.7.8 from oopsing not only on the SLES9 SP1
> > kernel but also the recent 2.6.10-ac series.
> >
> > (I could possibly _code_ it, but it'd be too invasive and I'm weary of
> > the side-effects it might have and the QA would take too long. There's a
> > number of potential cleanups like further consolidation between
> > drbd_prepare_req_write/_read and others, but I'd propose to do that for
> > the drbd-0.8 branch instead when we can do away with 2.4.)
> >
> > Please comment on the patch, I'd be grateful.
> >
> 
> Hi Lars,
> 
> the patch looks good so far. I am really happy that you have choosen
> to go the less intrusive way for drbd-07.
> 
> Changing it over to alloc_bio() is something for drbd-08.
> 
> [...]
>   ONLY_IN_26(unsigned int ee_size;)
>   ONLY_IN_26(sector_t ee_sector;)
> - // THINK: maybe we rather want bio_alloc(GFP_*,1)
> + // TODO: we rather want bio_alloc(GFP_*,1) all through the code!
>   ONLY_IN_26(struct bio_vec ee_bvec;)
> 
> I am wondering if with a private copy of the bio_vec if we already
> have a copy of the IO operations size and start sector that is 
> still in place after the IO operation completed.
> 
>  -> If this is the case we could drop the ee_size and ee_sector members
>     and take them form e.g. ee_bvec 
> 
> Jens, I guess you can answer that question  easily.

IO completion can change the vector offset and lengths for some cases of
partial io, notable where a device completes less than a complete
vector. So I'd say stay safe and retain your copy of those values.

-- 
Jens Axboe