linux-kernel - Re: [PATCH 4.19 01/16] block: introduce multi-page bvec helpers

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Date:   Thu, 11 Nov 2021 17:47:54 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Christoph Hellwig <hch@....de>, Omar Sandoval <osandov@...com>,
        Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Zubin Mithra <zsm@...omium.org>
Subject: Re: [PATCH 4.19 01/16] block: introduce multi-page bvec helpers

Hi!

> From: Ming Lei <ming.lei@...hat.com>
> 
> commit 3d75ca0adef4280650c6690a0c4702a74a6f3c95 upstream.
> 
> This patch introduces helpers of 'mp_bvec_iter_*' for multi-page bvec
> support.
> 
> The introduced helpers treate one bvec as real multi-page segment,
> which may include more than one pages.
> 
> The existed helpers of bvec_iter_* are interfaces for supporting current
> bvec iterator which is thought as single-page by drivers, fs, dm and
> etc. These introduced helpers will build single-page bvec in flight, so
> this way won't break current bio/bvec users, which needn't any
> change.

I don't understand why we have this in 4.19-stable. I don't see
followup patches needing it, and it does not claim to fix a bug.

> +#define mp_bvec_iter_bvec(bvec, iter)				\
> +((struct bio_vec) {						\
> +	.bv_page	= mp_bvec_iter_page((bvec), (iter)),	\
> +	.bv_len		= mp_bvec_iter_len((bvec), (iter)),	\
> +	.bv_offset	= mp_bvec_iter_offset((bvec), (iter)),	\
> +})
> +
> +/* For building single-page bvec in flight */
> + #define bvec_iter_offset(bvec, iter)				\
> +	(mp_bvec_iter_offset((bvec), (iter)) % PAGE_SIZE)
> +

Plus this one is strange. IIRC preprocessor directives have to put #
in column zero?

Best regards,
								Pavel
-- 
http://www.livejournal.com/~pavelmachek

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