linux-kernel - Re: [PATCH RFC v2 for-6.8/block 15/18] buffer: add a new helper to read sb block

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Message-ID: <20231211172708.qpuk4rkwq4u2zbmj@quack3>
Date:   Mon, 11 Dec 2023 18:27:08 +0100
From:   Jan Kara <jack@...e.cz>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     axboe@...nel.dk, roger.pau@...rix.com, colyli@...e.de,
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Subject: Re: [PATCH RFC v2 for-6.8/block 15/18] buffer: add a new helper to
 read sb block

On Mon 11-12-23 22:07:53, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> Unlike __bread_gfp(), ext4 has special handing while reading sb block:
> 
> 1) __GFP_NOFAIL is not set, and memory allocation can fail;
> 2) If buffer write failed before, set buffer uptodate and don't read
>    block from disk;
> 3) REQ_META is set for all IO, and REQ_PRIO is set for reading xattr;
> 4) If failed, return error ptr instead of NULL;
> 
> This patch add a new helper __bread_gfp2() that will match above 2 and 3(
> 1 will be used, and 4 will still be encapsulated by ext4), and prepare to
> prevent calling mapping_gfp_constraint() directly on bd_inode->i_mapping
> in ext4.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
...
> +/*
> + * This works like __bread_gfp() except:
> + * 1) If buffer write failed before, set buffer uptodate and don't read
> + * block from disk;
> + * 2) Caller can pass in additional op_flags like REQ_META;
> + */
> +struct buffer_head *
> +__bread_gfp2(struct block_device *bdev, sector_t block, unsigned int size,
> +	     blk_opf_t op_flags, gfp_t gfp)
> +{
> +	return bread_gfp(bdev, block, size, op_flags, gfp, true);
> +}
> +EXPORT_SYMBOL(__bread_gfp2);

__bread_gfp2() is not a great name, why not just using bread_gfp()
directly? I'm not a huge fan of boolean arguments but three different flags
arguments would be too much for my taste ;) so I guess I can live with
that.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR