linux-ext4 - Re: [PATCH 06/29] dax: move the partition alignment check into fs_dax_get_by

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Message-ID: <20211123222555.GE266024@magnolia>
Date:   Tue, 23 Nov 2021 14:25:55 -0800
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, dm-devel@...hat.com,
        linux-xfs@...r.kernel.org, nvdimm@...ts.linux.dev,
        linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 06/29] dax: move the partition alignment check into
 fs_dax_get_by_bdev

On Tue, Nov 09, 2021 at 09:32:46AM +0100, Christoph Hellwig wrote:
> fs_dax_get_by_bdev is the primary interface to find a dax device for a
> block device, so move the partition alignment check there instead of
> wiring it up through ->dax_supported.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/dax/super.c | 23 ++++++-----------------
>  1 file changed, 6 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 04fc680542e8d..482fe775324a4 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -93,6 +93,12 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
>  	if (!blk_queue_dax(bdev->bd_disk->queue))
>  		return NULL;
>  
> +	if ((get_start_sect(bdev) * SECTOR_SIZE) % PAGE_SIZE ||
> +	    (bdev_nr_sectors(bdev) * SECTOR_SIZE) % PAGE_SIZE) {

Do we have to be careful about 64-bit division here, or do we not
support DAX on 32-bit?

> +		pr_info("%pg: error: unaligned partition for dax\n", bdev);

I also wonder if this should be ratelimited...?

--D

> +		return NULL;
> +	}
> +
>  	id = dax_read_lock();
>  	dax_dev = xa_load(&dax_hosts, (unsigned long)bdev->bd_disk);
>  	if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
> @@ -107,10 +113,6 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
>  		struct block_device *bdev, int blocksize, sector_t start,
>  		sector_t sectors)
>  {
> -	pgoff_t pgoff, pgoff_end;
> -	sector_t last_page;
> -	int err;
> -
>  	if (blocksize != PAGE_SIZE) {
>  		pr_info("%pg: error: unsupported blocksize for dax\n", bdev);
>  		return false;
> @@ -121,19 +123,6 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
>  		return false;
>  	}
>  
> -	err = bdev_dax_pgoff(bdev, start, PAGE_SIZE, &pgoff);
> -	if (err) {
> -		pr_info("%pg: error: unaligned partition for dax\n", bdev);
> -		return false;
> -	}
> -
> -	last_page = PFN_DOWN((start + sectors - 1) * 512) * PAGE_SIZE / 512;
> -	err = bdev_dax_pgoff(bdev, last_page, PAGE_SIZE, &pgoff_end);
> -	if (err) {
> -		pr_info("%pg: error: unaligned partition for dax\n", bdev);
> -		return false;
> -	}
> -
>  	return true;
>  }
>  EXPORT_SYMBOL_GPL(generic_fsdax_supported);
> -- 
> 2.30.2
>