Re: [PATCH V3 05/12] xfs: Introduce xfs_dfork_nextents() helper

From: Dave Chinner <david@fromorbit.com>
To: Chandan Babu R <chandan.babu@oracle.com>
Cc: linux-xfs@vger.kernel.org, djwong@kernel.org
Subject: Re: [PATCH V3 05/12] xfs: Introduce xfs_dfork_nextents() helper
Date: Tue, 28 Sep 2021 08:46:49 +1000	[thread overview]
Message-ID: <20210927224649.GK1756565@dread.disaster.area> (raw)
In-Reply-To: <20210916100647.176018-6-chandan.babu@oracle.com>

On Thu, Sep 16, 2021 at 03:36:40PM +0530, Chandan Babu R wrote:
> This commit replaces the macro XFS_DFORK_NEXTENTS() with the helper function
> xfs_dfork_nextents(). As of this commit, xfs_dfork_nextents() returns the same
> value as XFS_DFORK_NEXTENTS(). A future commit which extends inode's extent
> counter fields will add more logic to this helper.
> 
> This commit also replaces direct accesses to xfs_dinode->di_[a]nextents
> with calls to xfs_dfork_nextents().
> 
> No functional changes have been made.
> 
> Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_format.h     | 28 +++++++++++++++++++++----
>  fs/xfs/libxfs/xfs_inode_buf.c  | 16 +++++++++-----
>  fs/xfs/libxfs/xfs_inode_fork.c | 10 +++++----
>  fs/xfs/scrub/inode.c           | 18 +++++++++-------
>  fs/xfs/scrub/inode_repair.c    | 38 +++++++++++++++++++++-------------
>  5 files changed, 75 insertions(+), 35 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index ed8a5354bcbf..b4638052801f 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -930,10 +930,30 @@ enum xfs_dinode_fmt {
>  	((w) == XFS_DATA_FORK ? \
>  		(dip)->di_format : \
>  		(dip)->di_aformat)
> -#define XFS_DFORK_NEXTENTS(dip,w) \
> -	((w) == XFS_DATA_FORK ? \
> -		be32_to_cpu((dip)->di_nextents) : \
> -		be16_to_cpu((dip)->di_anextents))
> +
> +static inline xfs_extnum_t
> +xfs_dfork_nextents(
> +	struct xfs_dinode	*dip,
> +	int			whichfork)
> +{
> +	xfs_extnum_t		nextents = 0;
> +
> +	switch (whichfork) {
> +	case XFS_DATA_FORK:
> +		nextents = be32_to_cpu(dip->di_nextents);
> +		break;
> +

No need for whitespace line after the break, and this could just
return the value directly.

> +	case XFS_ATTR_FORK:
> +		nextents = be16_to_cpu(dip->di_anextents);
> +		break;
> +
> +	default:
> +		ASSERT(0);
> +		break;
> +	}
> +
> +	return nextents;
> +}

I think that all the conditional inode fork macros
should be moved to libxfs/xfs_inode_fork.h as they are converted.

These macros are not acutally part of the on-disk format definition
(which is what xfs_format.h is supposed to contain) - it's code that
parses the on-disk format and that is supposed to be in
libxfs/xfs_inode_fork.[ch]....

Next thing: the caller almost always knows what fork it wants
the extents for - only 3 callers have a whichfork variable. So,
perhaps:

static inline xfs_extnum_t
xfs_dfork_data_extents(
	struct xfs_dinode	*dip)
{
	return be32_to_cpu(dip->di_nextents);
}

static inline xfs_extnum_t
xfs_dfork_attr_extents(
	struct xfs_dinode	*dip)
{
	return be16_to_cpu(dip->di_anextents);
}

static inline xfs_extnum_t
xfs_dfork_extents(
	struct xfs_dinode	*dip,
	int			whichfork)
{
	switch (whichfork) {
	case XFS_DATA_FORK:
		return xfs_dfork_data_extents(dip);
	case XFS_ATTR_FORK:
		return xfs_dfork_attr_extents(dip);
	default:
		ASSERT(0);
		break;
	}
	return 0;
}

So we don't have to rely on the compiler optimising away the switch
statement correctly to produce optimal code.

> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -342,9 +342,11 @@ xfs_dinode_verify_fork(
>  	struct xfs_mount	*mp,
>  	int			whichfork)
>  {
> -	xfs_extnum_t		di_nextents = XFS_DFORK_NEXTENTS(dip, whichfork);
> +	xfs_extnum_t		di_nextents;
>  	xfs_extnum_t		max_extents;
>  
> +	di_nextents = xfs_dfork_nextents(dip, whichfork);
> +
>  	switch (XFS_DFORK_FORMAT(dip, whichfork)) {
>  	case XFS_DINODE_FMT_LOCAL:
>  		/*
> @@ -474,6 +476,8 @@ xfs_dinode_verify(
>  	uint16_t		flags;
>  	uint64_t		flags2;
>  	uint64_t		di_size;
> +	xfs_extnum_t            nextents;
> +	xfs_rfsblock_t		nblocks;

That's a block number type, not a block count:

typedef uint64_t        xfs_rfsblock_t; /* blockno in filesystem (raw) */
....
typedef uint64_t        xfs_filblks_t;  /* number of blocks in a file */

The latter is the appropriate type to use here.

Oh, the struct xfs_inode and the struct xfs_log_dinode makes
this same type mistake. Ok, that's a cleanup for another day....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com