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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Date:   Tue, 12 Dec 2023 09:32:10 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Jan Kara <jack@...e.cz>, Yu Kuai <yukuai1@...weicloud.com>
Cc:     axboe@...nel.dk, roger.pau@...rix.com, colyli@...e.de,
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        yi.zhang@...wei.com, "yangerkun@...wei.com" <yangerkun@...wei.com>,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC v2 for-6.8/block 15/18] buffer: add a new helper to
 read sb block

Hi,

在 2023/12/12 1:27, Jan Kara 写道:
> 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.

I agree that __bread_gfp2 is not a greate name, if possible, I'll try to
figure out a better name for v3.

Thanks for reviewing this patchset!
Kuai
> 
> 								Honza
>