linux-kernel - Re: [PATCH V7 4/9] fs/xfs: Make DAX mount option a tri-state

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Date:   Mon, 13 Apr 2020 08:46:19 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Jeff Moyer <jmoyer@...hat.com>, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V7 4/9] fs/xfs: Make DAX mount option a tri-state

On Sun, Apr 12, 2020 at 10:40:41PM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> As agreed upon[1].  We make the dax mount option a tri-state.  '-o dax'
> continues to operate the same.  We add 'always', 'never', and 'inode'
> (default).
> 
> [1] https://lore.kernel.org/lkml/20200405061945.GA94792@iweiny-DESK2.sc.intel.com/
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> Changes from v6:
> 	Use 2 flag bits rather than a field.
> 	change iflag to inode
> 
> Changes from v5:
> 	New Patch
> ---
>  fs/xfs/xfs_mount.h |  3 ++-
>  fs/xfs/xfs_super.c | 44 ++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 42 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> index 88ab09ed29e7..d581b990e59a 100644
> --- a/fs/xfs/xfs_mount.h
> +++ b/fs/xfs/xfs_mount.h
> @@ -233,7 +233,8 @@ typedef struct xfs_mount {
>  						   allocator */
>  #define XFS_MOUNT_NOATTR2	(1ULL << 25)	/* disable use of attr2 format */
>  
> -#define XFS_MOUNT_DAX		(1ULL << 62)	/* TEST ONLY! */
> +#define XFS_MOUNT_DAX		(1ULL << 62)
> +#define XFS_MOUNT_NODAX		(1ULL << 63)
>  
>  /*
>   * Max and min values for mount-option defined I/O
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 2094386af8ac..d7bd8f5e00c9 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -47,6 +47,32 @@ static struct kset *xfs_kset;		/* top-level xfs sysfs dir */
>  static struct xfs_kobj xfs_dbg_kobj;	/* global debug sysfs attrs */
>  #endif
>  
> +enum {
> +	XFS_DAX_INODE = 0,
> +	XFS_DAX_ALWAYS = 1,
> +	XFS_DAX_NEVER = 2,
> +};
> +
> +static void xfs_mount_set_dax_mode(struct xfs_mount *mp, u32 val)
> +{
> +	if (val == XFS_DAX_INODE) {
> +		mp->m_flags &= ~(XFS_MOUNT_DAX | XFS_MOUNT_NODAX);
> +	} else if (val == XFS_DAX_ALWAYS) {
> +		mp->m_flags &= ~XFS_MOUNT_NODAX;
> +		mp->m_flags |= XFS_MOUNT_DAX;
> +	} else if (val == XFS_DAX_NEVER) {
> +		mp->m_flags &= ~XFS_MOUNT_DAX;
> +		mp->m_flags |= XFS_MOUNT_NODAX;
> +	}
> +}
> +
> +static const struct constant_table dax_param_enums[] = {
> +	{"inode",	XFS_DAX_INODE },
> +	{"always",	XFS_DAX_ALWAYS },
> +	{"never",	XFS_DAX_NEVER },
> +	{}

I think that the dax_param_enums table (and the unnamed enum defining
XFS_DAX_*) probably ought to be part of the VFS so that you don't have
to duplicate these two pieces whenever it's time to bring ext4 in line
with XFS.

That probably doesn't need to be done right away, though...

Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>

--D


> +};
> +
>  /*
>   * Table driven mount option parser.
>   */
> @@ -59,7 +85,7 @@ enum {
>  	Opt_filestreams, Opt_quota, Opt_noquota, Opt_usrquota, Opt_grpquota,
>  	Opt_prjquota, Opt_uquota, Opt_gquota, Opt_pquota,
>  	Opt_uqnoenforce, Opt_gqnoenforce, Opt_pqnoenforce, Opt_qnoenforce,
> -	Opt_discard, Opt_nodiscard, Opt_dax,
> +	Opt_discard, Opt_nodiscard, Opt_dax, Opt_dax_enum,
>  };
>  
>  static const struct fs_parameter_spec xfs_fs_parameters[] = {
> @@ -103,6 +129,7 @@ static const struct fs_parameter_spec xfs_fs_parameters[] = {
>  	fsparam_flag("discard",		Opt_discard),
>  	fsparam_flag("nodiscard",	Opt_nodiscard),
>  	fsparam_flag("dax",		Opt_dax),
> +	fsparam_enum("dax",		Opt_dax_enum, dax_param_enums),
>  	{}
>  };
>  
> @@ -129,7 +156,6 @@ xfs_fs_show_options(
>  		{ XFS_MOUNT_GRPID,		",grpid" },
>  		{ XFS_MOUNT_DISCARD,		",discard" },
>  		{ XFS_MOUNT_LARGEIO,		",largeio" },
> -		{ XFS_MOUNT_DAX,		",dax" },
>  		{ 0, NULL }
>  	};
>  	struct xfs_mount	*mp = XFS_M(root->d_sb);
> @@ -185,6 +211,13 @@ xfs_fs_show_options(
>  	if (!(mp->m_qflags & XFS_ALL_QUOTA_ACCT))
>  		seq_puts(m, ",noquota");
>  
> +	if (mp->m_flags & XFS_MOUNT_DAX)
> +		seq_puts(m, ",dax=always");
> +	else if (mp->m_flags & XFS_MOUNT_NODAX)
> +		seq_puts(m, ",dax=never");
> +	else
> +		seq_puts(m, ",dax=inode");
> +
>  	return 0;
>  }
>  
> @@ -1244,7 +1277,10 @@ xfs_fc_parse_param(
>  		return 0;
>  #ifdef CONFIG_FS_DAX
>  	case Opt_dax:
> -		mp->m_flags |= XFS_MOUNT_DAX;
> +		xfs_mount_set_dax_mode(mp, XFS_DAX_ALWAYS);
> +		return 0;
> +	case Opt_dax_enum:
> +		xfs_mount_set_dax_mode(mp, result.uint_32);
>  		return 0;
>  #endif
>  	default:
> @@ -1451,7 +1487,7 @@ xfs_fc_fill_super(
>  		if (!rtdev_is_dax && !datadev_is_dax) {
>  			xfs_alert(mp,
>  			"DAX unsupported by block device. Turning off DAX.");
> -			mp->m_flags &= ~XFS_MOUNT_DAX;
> +			xfs_mount_set_dax_mode(mp, XFS_DAX_NEVER);
>  		}
>  		if (xfs_sb_version_hasreflink(&mp->m_sb)) {
>  			xfs_alert(mp,
> -- 
> 2.25.1
>