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

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Message-ID: <ZV2xlDgkLpPeUhHN@fedora>
Date:   Wed, 22 Nov 2023 15:45:24 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Yu Kuai <yukuai1@...weicloud.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

On Tue, Nov 21, 2023 at 11:28:56PM -0800, Christoph Hellwig wrote:
> > +	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.
 
All the existed 'bool' flags are not atomic RW, so I think it isn't
necessary to define 'bd_flags' as 'unsigned long' for replacing them.

Thanks, 
Ming