linux-kernel - Re: [PATCH 01/27] block: bio: introduce 4 helpers for cleanup

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Message-ID: <CACVXFVN78cA3Lk4H6xgEVQCguqdn3HPpOAtsPHMqXpD9KDHCCQ@mail.gmail.com>
Date:	Wed, 6 Apr 2016 09:34:34 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Kent Overstreet <kent.overstreet@...il.com>
Cc:	Jens Axboe <axboe@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
	Boaz Harrosh <boaz@...xistor.com>, Jan Kara <jack@...e.cz>,
	Keith Busch <keith.busch@...el.com>, Tejun Heo <tj@...nel.org>,
	Mike Snitzer <snitzer@...hat.com>
Subject: Re: [PATCH 01/27] block: bio: introduce 4 helpers for cleanup

On Wed, Apr 6, 2016 at 8:18 AM, Kent Overstreet
<kent.overstreet@...il.com> 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?


Thanks,
Ming Lei