linux-ext4 - Re: [PATCH RFC 4/8] fs/ext4: Introduce DAX inode flag

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Date:   Wed, 15 Apr 2020 14:08:46 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 4/8] fs/ext4: Introduce DAX inode flag

On Mon 13-04-20 21:00:26, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Add a flag to preserve FS_XFLAG_DAX in the ext4 inode.
> 
> Set the flag to be user visible and changeable.  Set the flag to be
> inherited.  Allow applications to change the flag at any time.
> 
> Finally, on regular files, flag the inode to not be cached to facilitate
> changing S_DAX on the next creation of the inode.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  fs/ext4/ext4.h  | 13 +++++++++----
>  fs/ext4/ioctl.c | 21 ++++++++++++++++++++-
>  2 files changed, 29 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 61b37a052052..434021fcec88 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -415,13 +415,16 @@ struct flex_groups {
>  #define EXT4_VERITY_FL			0x00100000 /* Verity protected inode */
>  #define EXT4_EA_INODE_FL	        0x00200000 /* Inode used for large EA */
>  #define EXT4_EOFBLOCKS_FL		0x00400000 /* Blocks allocated beyond EOF */
> +
> +#define EXT4_DAX_FL			0x00800000 /* Inode is DAX */
> +

You seem to be using somewhat older kernel... EXT4_EOFBLOCKS_FL doesn't
exist anymore (but still it's good to leave it reserved for some time so
the value you've chosen is OK).

> @@ -813,6 +818,17 @@ static int ext4_ioctl_get_es_cache(struct file *filp, unsigned long arg)
>  	return error;
>  }
>  
> +static void ext4_dax_dontcache(struct inode *inode, unsigned int flags)
> +{
> +	struct ext4_inode_info *ei = EXT4_I(inode);
> +
> +	if (S_ISDIR(inode->i_mode))
> +		return;
> +
> +	if ((ei->i_flags ^ flags) == EXT4_DAX_FL)
> +		inode->i_state |= I_DONTCACHE;
> +}
> +

You probably want to use the function you've introduced in the XFS series
here...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR