linux-ext4 - Re: [PATCH V3 7/8] fs/ext4: Introduce DAX inode flag

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Date:   Wed, 20 May 2020 16:11:38 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-ext4@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Eric Biggers <ebiggers@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 7/8] fs/ext4: Introduce DAX inode flag

On Tue 19-05-20 22:57:52, 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 with the
> exception of if VERITY or ENCRYPT is set.
> 
> Disallow setting VERITY or ENCRYPT if DAX is set.
> 
> 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>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

One comment below:

> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 5ba65eb0e2ef..be9713e898eb 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1323,6 +1323,9 @@ static int ext4_set_context(struct inode *inode, const void *ctx, size_t len,
>  	if (WARN_ON_ONCE(IS_DAX(inode) && i_size_read(inode)))
>  		return -EINVAL;

AFAIU this check is here so that fscrypt_inherit_context() is able call us
and we can clear S_DAX flag. So can't we rather move this below the
EXT4_INODE_DAX check and change this to

	IS_DAX(inode) && !(inode->i_flags & I_NEW)

? Because as I'm reading the code now, this should never trigger?

>  
> +	if (ext4_test_inode_flag(inode, EXT4_INODE_DAX))
> +		return -EOPNOTSUPP;
> +

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