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Date:   Thu, 1 Feb 2018 14:46:51 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     linux-xfs@...r.kernel.org, ross.zwisler@...ux.intel.com,
        linux-ext4@...r.kernel.org, dan.j.williams@...el.com,
        linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 2 1/2] dax: change bdev_dax_supported() to take a
 block_device as input

On Thu, Feb 01, 2018 at 01:32:59PM -0700, Dave Jiang wrote:
> This is in preparation to support DAX for realtime device on XFS.
> bdev_dax_supported() will be taking a block_device as input instead of
> a superblock. The only place a super_block is used in this function is
> providing the id for debug outputs. Also __bdev_dax_supported()
> will be removed since it just directly calls bdev_dax_supported()
> and is not reference by any other code.
> 
> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> ---
>  drivers/dax/super.c |   33 ++++++++++++++++-----------------
>  fs/ext2/super.c     |    2 +-
>  fs/ext4/super.c     |    2 +-
>  fs/xfs/xfs_ioctl.c  |    2 +-
>  fs/xfs/xfs_super.c  |    2 +-
>  include/linux/dax.h |    8 ++------
>  6 files changed, 22 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 473af694ad1c..3bdf6787b6df 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -70,11 +70,10 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
>  	return fs_dax_get_by_host(bdev->bd_disk->disk_name);
>  }
>  EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
> -#endif
>  
>  /**
> - * __bdev_dax_supported() - Check if the device supports dax for filesystem
> - * @sb: The superblock of the device
> + * bdev_dax_supported() - Check if the device supports dax for filesystem
> + * @sb: The block_device of the device
>   * @blocksize: The block size of the device
>   *
>   * This is a library function for filesystems to check if the block device
> @@ -82,9 +81,8 @@ EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
>   *
>   * Return: negative errno if unsupported, 0 if supported.
>   */
> -int __bdev_dax_supported(struct super_block *sb, int blocksize)
> +int bdev_dax_supported(struct block_device *bdev, int blocksize)

Looking ahead to filesystems that can span multiple dax devices, perhaps
it would be better to be able topass in the bdev that we want to check?

int bdev_dax_supported(sb, bdev, blocksize)
{
	/* same tests we do today... */
}

int sb_dax_supported(sb, blocksize)
{
	return bdev_dax_supported(sb, sb->s_bdev, blocksize);
}

That way a single bdev filesystem (ext4) can retain the same api it uses
today, and two-bdev filesystems (xfs) can specify which bdev to check.

(Continuing review in the next patch...)

--D

>  {
> -	struct block_device *bdev = sb->s_bdev;
>  	struct dax_device *dax_dev;
>  	pgoff_t pgoff;
>  	int err, id;
> @@ -93,22 +91,22 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize)
>  	long len;
>  
>  	if (blocksize != PAGE_SIZE) {
> -		pr_debug("VFS (%s): error: unsupported blocksize for dax\n",
> -				sb->s_id);
> +		pr_debug("bdev (%d:%d): error: unsupported blocksize for dax\n",
> +				MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
>  		return -EINVAL;
>  	}
>  
>  	err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
>  	if (err) {
> -		pr_debug("VFS (%s): error: unaligned partition for dax\n",
> -				sb->s_id);
> +		pr_debug("bdev (%d:%d): error: unaligned partition for dax\n",
> +				MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
>  		return err;
>  	}
>  
>  	dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
>  	if (!dax_dev) {
> -		pr_debug("VFS (%s): error: device does not support dax\n",
> -				sb->s_id);
> +		pr_debug("bdev (%d:%d): error: device does not support dax\n",
> +				MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
>  		return -EOPNOTSUPP;
>  	}
>  
> @@ -119,8 +117,8 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize)
>  	put_dax(dax_dev);
>  
>  	if (len < 1) {
> -		pr_debug("VFS (%s): error: dax access failed (%ld)\n",
> -				sb->s_id, len);
> +		pr_debug("bdev (%d:%d): error: dax access failed (%ld)\n",
> +				MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev), len);
>  		return len < 0 ? len : -EIO;
>  	}
>  
> @@ -128,15 +126,16 @@ int __bdev_dax_supported(struct super_block *sb, int blocksize)
>  			|| pfn_t_devmap(pfn))
>  		/* pass */;
>  	else {
> -		pr_debug("VFS (%s): error: dax support not enabled\n",
> -				sb->s_id);
> +		pr_debug("bdev (%d:%d): error: dax support not enabled\n",
> +				MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
>  		return -EOPNOTSUPP;
>  	}
>  
>  	return 0;
>  }
> -EXPORT_SYMBOL_GPL(__bdev_dax_supported);
> -#endif
> +EXPORT_SYMBOL_GPL(bdev_dax_supported);
> +#endif /* CONFIG_FS_DAX */
> +#endif /* CONFIG_BLOCK */
>  
>  enum dax_device_flags {
>  	/* !alive + rcu grace period == no new operations / mappings */
> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> index 38f9222606ee..a0de090b18d5 100644
> --- a/fs/ext2/super.c
> +++ b/fs/ext2/super.c
> @@ -958,7 +958,7 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
>  	blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
>  
>  	if (sbi->s_mount_opt & EXT2_MOUNT_DAX) {
> -		err = bdev_dax_supported(sb, blocksize);
> +		err = bdev_dax_supported(sb->s_bdev, blocksize);
>  		if (err) {
>  			ext2_msg(sb, KERN_ERR,
>  				"DAX unsupported by block device. Turning off DAX.");
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 18873ea89e08..7ebc8d5cab8c 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3712,7 +3712,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  					" that may contain inline data");
>  			sbi->s_mount_opt &= ~EXT4_MOUNT_DAX;
>  		}
> -		err = bdev_dax_supported(sb, blocksize);
> +		err = bdev_dax_supported(sb->s_bdev, blocksize);
>  		if (err) {
>  			ext4_msg(sb, KERN_ERR,
>  				"DAX unsupported by block device. Turning off DAX.");
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 20dc65fef6a4..5fd4d50eb1c6 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1102,7 +1102,7 @@ xfs_ioctl_setattr_dax_invalidate(
>  	if (fa->fsx_xflags & FS_XFLAG_DAX) {
>  		if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
>  			return -EINVAL;
> -		if (bdev_dax_supported(sb, sb->s_blocksize) < 0)
> +		if (bdev_dax_supported(sb->s_bdev, sb->s_blocksize) < 0)
>  			return -EINVAL;
>  	}
>  
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 1dacccc367f8..e8a687232614 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -1652,7 +1652,7 @@ xfs_fs_fill_super(
>  		xfs_warn(mp,
>  		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
>  
> -		error = bdev_dax_supported(sb, sb->s_blocksize);
> +		error = bdev_dax_supported(sb->s_bdev, sb->s_blocksize);
>  		if (error) {
>  			xfs_alert(mp,
>  			"DAX unsupported by block device. Turning off DAX.");
> diff --git a/include/linux/dax.h b/include/linux/dax.h
> index 5258346c558c..a31a7e3f929b 100644
> --- a/include/linux/dax.h
> +++ b/include/linux/dax.h
> @@ -40,11 +40,7 @@ static inline void put_dax(struct dax_device *dax_dev)
>  
>  int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
>  #if IS_ENABLED(CONFIG_FS_DAX)
> -int __bdev_dax_supported(struct super_block *sb, int blocksize);
> -static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
> -{
> -	return __bdev_dax_supported(sb, blocksize);
> -}
> +int bdev_dax_supported(struct block_device *bdev, int blocksize);
>  
>  static inline struct dax_device *fs_dax_get_by_host(const char *host)
>  {
> @@ -58,7 +54,7 @@ static inline void fs_put_dax(struct dax_device *dax_dev)
>  
>  struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
>  #else
> -static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
> +static inline int bdev_dax_supported(struct block_device *bdev, int blocksize)
>  {
>  	return -EOPNOTSUPP;
>  }
> 
> --
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