linux-kernel - Re: [PATCH V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to

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Date:   Wed, 8 Apr 2020 12:08:27 +1000
From:   Dave Chinner <david@...morbit.com>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.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 V6 6/8] fs/xfs: Combine xfs_diflags_to_linux() and
 xfs_diflags_to_iflags()

On Tue, Apr 07, 2020 at 11:29:56AM -0700, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> The functionality in xfs_diflags_to_linux() and xfs_diflags_to_iflags() are
> nearly identical.  The only difference is that *_to_linux() is called after
> inode setup and disallows changing the DAX flag.
> 
> Combining them can be done with a flag which indicates if this is the initial
> setup to allow the DAX flag to be properly set only at init time.
> 
> So remove xfs_diflags_to_linux() and call the modified xfs_diflags_to_iflags()
> directly.
> 
> While we are here simplify xfs_diflags_to_iflags() to take struct xfs_inode and
> use xfs_ip2xflags() to ensure future diflags are included correctly.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> 
> ---
> Changes from V5:
> 	The functions are no longer identical so we can only combine
> 	them rather than deleting one completely.  This is reflected in
> 	the new init parameter.
> ---
>  fs/xfs/xfs_inode.h |  1 +
>  fs/xfs/xfs_ioctl.c | 33 +--------------------------------
>  fs/xfs/xfs_iops.c  | 42 +++++++++++++++++++++++++++---------------
>  3 files changed, 29 insertions(+), 47 deletions(-)
> 
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 492e53992fa9..e76ed9ca17f7 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -466,6 +466,7 @@ int	xfs_break_layouts(struct inode *inode, uint *iolock,
>  /* from xfs_iops.c */
>  extern void xfs_setup_inode(struct xfs_inode *ip);
>  extern void xfs_setup_iops(struct xfs_inode *ip);
> +extern void xfs_diflags_to_iflags(struct xfs_inode *ip, bool init);
>  
>  /*
>   * When setting up a newly allocated inode, we need to call
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index d42de92cb283..c6cd92ef4a05 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1100,37 +1100,6 @@ xfs_flags2diflags2(
>  	return di_flags2;
>  }
>  
> -STATIC void
> -xfs_diflags_to_linux(
> -	struct xfs_inode	*ip)
> -{
> -	struct inode		*inode = VFS_I(ip);
> -	unsigned int		xflags = xfs_ip2xflags(ip);
> -
> -	if (xflags & FS_XFLAG_IMMUTABLE)
> -		inode->i_flags |= S_IMMUTABLE;
> -	else
> -		inode->i_flags &= ~S_IMMUTABLE;
> -	if (xflags & FS_XFLAG_APPEND)
> -		inode->i_flags |= S_APPEND;
> -	else
> -		inode->i_flags &= ~S_APPEND;
> -	if (xflags & FS_XFLAG_SYNC)
> -		inode->i_flags |= S_SYNC;
> -	else
> -		inode->i_flags &= ~S_SYNC;
> -	if (xflags & FS_XFLAG_NOATIME)
> -		inode->i_flags |= S_NOATIME;
> -	else
> -		inode->i_flags &= ~S_NOATIME;
> -#if 0	/* disabled until the flag switching races are sorted out */
> -	if (xflags & FS_XFLAG_DAX)
> -		inode->i_flags |= S_DAX;
> -	else
> -		inode->i_flags &= ~S_DAX;
> -#endif

So this variant will set the flag in the inode if the disk inode
flag is set, otherwise it will clear it.  It does it with if/else
branches.


> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index e07f7b641226..a4ac8568c8c7 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -1259,7 +1259,7 @@ xfs_inode_supports_dax(
>  	return xfs_inode_buftarg(ip)->bt_daxdev != NULL;
>  }
>  
> -STATIC bool
> +static bool
>  xfs_inode_enable_dax(
>  	struct xfs_inode *ip)
>  {

This belongs in the previous patch.

> @@ -1272,26 +1272,38 @@ xfs_inode_enable_dax(
>  	return false;
>  }
>  
> -STATIC void
> +void
>  xfs_diflags_to_iflags(
> -	struct inode		*inode,
> -	struct xfs_inode	*ip)
> +	struct xfs_inode	*ip,
> +	bool init)
>  {
> -	uint16_t		flags = ip->i_d.di_flags;
> -
> -	inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC |
> -			    S_NOATIME | S_DAX);

And this code cleared all the flags in the inode first, then
set them if the disk inode flag is set. This does not require
branches, resulting in more readable code and better code
generation.

> +	struct inode		*inode = VFS_I(ip);
> +	uint			diflags = xfs_ip2xflags(ip);
>  
> -	if (flags & XFS_DIFLAG_IMMUTABLE)
> +	if (diflags & FS_XFLAG_IMMUTABLE)
>  		inode->i_flags |= S_IMMUTABLE;
> -	if (flags & XFS_DIFLAG_APPEND)
> +	else
> +		inode->i_flags &= ~S_IMMUTABLE;

> +	if (diflags & FS_XFLAG_APPEND)
>  		inode->i_flags |= S_APPEND;
> -	if (flags & XFS_DIFLAG_SYNC)
> +	else
> +		inode->i_flags &= ~S_APPEND;
> +	if (diflags & FS_XFLAG_SYNC)
>  		inode->i_flags |= S_SYNC;
> -	if (flags & XFS_DIFLAG_NOATIME)
> +	else
> +		inode->i_flags &= ~S_SYNC;
> +	if (diflags & FS_XFLAG_NOATIME)
>  		inode->i_flags |= S_NOATIME;
> -	if (xfs_inode_enable_dax(ip))
> -		inode->i_flags |= S_DAX;
> +	else
> +		inode->i_flags &= ~S_NOATIME;
> +
> +	/* Only toggle the dax flag when initializing */
> +	if (init) {
> +		if (xfs_inode_enable_dax(ip))
> +			inode->i_flags |= S_DAX;
> +		else
> +			inode->i_flags &= ~S_DAX;
> +	}
>  }

IOWs, this:

        struct inode            *inode = VFS_I(ip);
        unsigned int            xflags = xfs_ip2xflags(ip);
        unsigned int            flags = 0;

        if (xflags & FS_XFLAG_IMMUTABLE)
                flags |= S_IMMUTABLE;
        if (xflags & FS_XFLAG_APPEND)
                flags |= S_APPEND;
        if (xflags & FS_XFLAG_SYNC)
                flags |= S_SYNC;
        if (xflags & FS_XFLAG_NOATIME)
                flags |= S_NOATIME;
	if ((xflags & FS_XFLAG_DAX) && init)
		flags |= S_DAX;

        inode->i_flags &= ~(S_IMMUTABLE | S_APPEND | S_SYNC | S_NOATIME);
        inode->i_flags |= flags;

ends up being much easier to read and results in better code
generation. And we don't need to clear the S_DAX flag when "init" is
set, because we are starting from an inode that has no flags set
(because init!)...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com