linux-kernel - Re: [PATCH v3 2/3] block: introduce new field bd_flags in block

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Message-ID: <ZV2tuLCH2cPXxQ30@infradead.org>
Date:   Tue, 21 Nov 2023 23:28:56 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     ming.lei@...hat.com, axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yukuai3@...wei.com,
        yi.zhang@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH v3 2/3] block: introduce new field bd_flags in
 block_device

> +	if (partno && bdev_flagged(disk->part0, BD_FLAG_HAS_SUBMIT_BIO))
> +		bdev_set_flag(bdev, BD_FLAG_HAS_SUBMIT_BIO);
>  	else
> +		bdev_clear_flag(bdev, BD_FLAG_HAS_SUBMIT_BIO);

While the block layer has a bit of history of using wrappers for
testing, setting and clearing flags, I have to say I always find them
rather confusing when reading the code.

> +#define BD_FLAG_READ_ONLY	0 /* read-only-policy */

I know this is copied from the existing field, but can you expand
it a bit?

> +#define BD_FLAG_WRITE_HOLDER	1
> +#define BD_FLAG_HAS_SUBMIT_BIO	2
> +#define BD_FLAG_MAKE_IT_FAIL	3

And also write comments for these. 

> +
>  struct block_device {
>  	sector_t		bd_start_sect;
>  	sector_t		bd_nr_sectors;
> @@ -44,10 +49,8 @@ struct block_device {
>  	struct request_queue *	bd_queue;
>  	struct disk_stats __percpu *bd_stats;
>  	unsigned long		bd_stamp;
> -	bool			bd_read_only;	/* read-only policy */
> +	unsigned short		bd_flags;

I suspect you really need an unsigned long and atomic bit ops here.
Even a lock would probably not work on alpha as it could affect
the other fields in the same 32-bit alignment.