linux-kernel - Re: [PATCH 45/60] block: bio: introduce bio_for_each_segment_all

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Date:   Tue, 1 Nov 2016 06:46:15 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     "Theodore Ts'o" <tytso@....edu>, Ming Lei <tom.leiming@...il.com>,
        Jens Axboe <axboe@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Christie <mchristi@...hat.com>,
        Hannes Reinecke <hare@...e.com>,
        Keith Busch <keith.busch@...el.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Bart Van Assche <bart.vanassche@...disk.com>
Subject: Re: [PATCH 45/60] block: bio: introduce bio_for_each_segment_all_rd()
 and its write pair

On Mon, Oct 31, 2016 at 9:59 PM, Theodore Ts'o <tytso@....edu> wrote:
> On Sat, Oct 29, 2016 at 04:08:44PM +0800, Ming Lei wrote:
>> This patches introduce bio_for_each_segment_all_rd() and
>> bio_for_each_segment_all_wt().
>>
>> bio_for_each_segment_all_rd() is for replacing
>> bio_for_each_segment_all() in case the bvec from bio->bi_io_vec
>> is accessed as readonly.
>>
>> bio_for_each_segment_all_wt() is for replacing
>> bio_for_each_segment_all() in case the bvec from bio->bi_io_vec
>> need to be updated.
>
> What is _rd and _wt supposed to stand for?  And speaking more

As Christoph replied, _rd means read, which said the bvec pointed by
the iterator variable(bvec pointer) is read-only, and the bvec table
can't be written into via this usage any more. Maybe
bio_for_each_segment_all_ro is better?

On the other hand, _wr meands write, which said the bvec pointed by
the iterator variable(bvec pointer) can be written to. Maybe we can use
original bio_for_each_segment_all() for it?

> generally, could you write up some more detailed notes about all of
> the various new functions they have been added, when they should be
> used, and some kind of roadmap about how things are supposed to work
> beyond the very high-level description in the introduction in your
> patch series?  Ideally it would go into the Documentation directory,
> so that after this patch set gets applied, people will be able to
> refer to it to understand how things are supposed to work.

In the next post, I will add comment on the two helpers, thanks for
your review.

Thanks,
Ming

>
> Thanks!!
>
>                                                 - Ted



-- 
Ming Lei