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Date:   Fri, 21 Jul 2023 08:24:23 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        "Darrick J. Wong" <djwong@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH 6/6] fs: add CONFIG_BUFFER_HEAD
Message-ID: <20230721062423.GA20845@lst.de>
References: <20230720140452.63817-1-hch@lst.de> <20230720140452.63817-7-hch@lst.de> <ZLlId9+kXl5Tb7wj@casper.infradead.org>
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On Thu, Jul 20, 2023 at 03:45:11PM +0100, Matthew Wilcox wrote:
> On Thu, Jul 20, 2023 at 04:04:52PM +0200, Christoph Hellwig wrote:
> > @@ -400,7 +391,8 @@ static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> >  	iomap->type = IOMAP_MAPPED;
> >  	iomap->addr = iomap->offset;
> >  	iomap->length = isize - iomap->offset;
> > -	iomap->flags |= IOMAP_F_BUFFER_HEAD;
> > +	if (IS_ENABLED(CONFIG_BUFFER_HEAD))
> > +		iomap->flags |= IOMAP_F_BUFFER_HEAD;
> 
> Wouldn't it be simpler to do ...
> 
> +#ifdef CONFIG_BUFFER_HEAD
>  #define IOMAP_F_BUFFER_HEAD     (1U << 4)
> +#else
> +#define IOMAP_F_BUFFER_HEAD	0
> +#endif
> 
> in include/linux/iomap.h ?

> ... because this function then goes away.

I guess we could do that.  It is less intrusive, but I have to say I find
flags that get defined away to 0 fairly confusing for the reader.