linux-kernel - Re: [PATCH RESEND] erofs: use Z_EROFS_LCLUSTER_TYPE

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Message-ID: <7a9a2ead-88e5-4b53-9322-c649c92e73c2@huawei.com>
Date: Fri, 7 Feb 2025 15:33:18 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Hongzhen Luo <hongzhen@...ux.alibaba.com>, <linux-erofs@...ts.ozlabs.org>
CC: <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] erofs: use Z_EROFS_LCLUSTER_TYPE_MAX to simplify
 switches



On 2025/2/7 14:41, Hongzhen Luo wrote:
> There's no need to enumerate each type.  No logic changes.
> 
> Signed-off-by: Hongzhen Luo <hongzhen@...ux.alibaba.com>
> ---
>   fs/erofs/zmap.c | 59 ++++++++++++++++++-------------------------------
>   1 file changed, 22 insertions(+), 37 deletions(-)
> 
> diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> index 689437e99a5a..0ee78413bfd5 100644
> --- a/fs/erofs/zmap.c
> +++ b/fs/erofs/zmap.c
> @@ -265,24 +265,20 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
>   		if (err)
>   			return err;
>   
> -		switch (m->type) {
> -		case Z_EROFS_LCLUSTER_TYPE_NONHEAD:
> +		if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {
>   			lookback_distance = m->delta[0];
>   			if (!lookback_distance)
>   				goto err_bogus;
>   			continue;
> -		case Z_EROFS_LCLUSTER_TYPE_PLAIN:
> -		case Z_EROFS_LCLUSTER_TYPE_HEAD1:
> -		case Z_EROFS_LCLUSTER_TYPE_HEAD2:
> +		} else if (m->type < Z_EROFS_LCLUSTER_TYPE_MAX) {
>   			m->headtype = m->type;
>   			m->map->m_la = (lcn << lclusterbits) | m->clusterofs;
>   			return 0;
> -		default:
> -			erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
> -				  m->type, lcn, vi->nid);
> -			DBG_BUGON(1);
> -			return -EOPNOTSUPP;
>   		}
> +		erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
> +			  m->type, lcn, vi->nid);
> +		DBG_BUGON(1);
> +		return -EOPNOTSUPP;

May be it would be easier to understand if you put the exception branch 
at the beginning. Such as:

if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
   // return -EOPNOTSUPP;
}

if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {
   // do something
}

// do something for other cases..

This is also useful for other places. :)

Thanks,
Hongbo

>   	}
>   err_bogus:
>   	erofs_err(sb, "bogus lookback distance %u @ lcn %lu of nid %llu",
> @@ -329,35 +325,28 @@ static int z_erofs_get_extent_compressedlen(struct z_erofs_maprecorder *m,
>   	DBG_BUGON(lcn == initial_lcn &&
>   		  m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD);
>   
> -	switch (m->type) {
> -	case Z_EROFS_LCLUSTER_TYPE_PLAIN:
> -	case Z_EROFS_LCLUSTER_TYPE_HEAD1:
> -	case Z_EROFS_LCLUSTER_TYPE_HEAD2:
> +	if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {
> +		if (m->delta[0] != 1) {
> +			erofs_err(sb, "bogus CBLKCNT @ lcn %lu of nid %llu", lcn, vi->nid);
> +			DBG_BUGON(1);
> +			return -EFSCORRUPTED;
> +		}
> +		if (m->compressedblks)
> +			goto out;
> +	} else if (m->type < Z_EROFS_LCLUSTER_TYPE_MAX) {
>   		/*
>   		 * if the 1st NONHEAD lcluster is actually PLAIN or HEAD type
>   		 * rather than CBLKCNT, it's a 1 block-sized pcluster.
>   		 */
>   		m->compressedblks = 1;
> -		break;
> -	case Z_EROFS_LCLUSTER_TYPE_NONHEAD:
> -		if (m->delta[0] != 1)
> -			goto err_bonus_cblkcnt;
> -		if (m->compressedblks)
> -			break;
> -		fallthrough;
> -	default:
> -		erofs_err(sb, "cannot found CBLKCNT @ lcn %lu of nid %llu", lcn,
> -			  vi->nid);
> -		DBG_BUGON(1);
> -		return -EFSCORRUPTED;
> +		goto out;
>   	}
> +	erofs_err(sb, "cannot found CBLKCNT @ lcn %lu of nid %llu", lcn, vi->nid);
> +	DBG_BUGON(1);
> +	return -EFSCORRUPTED;
>   out:
>   	m->map->m_plen = erofs_pos(sb, m->compressedblks);
>   	return 0;
> -err_bonus_cblkcnt:
> -	erofs_err(sb, "bogus CBLKCNT @ lcn %lu of nid %llu", lcn, vi->nid);
> -	DBG_BUGON(1);
> -	return -EFSCORRUPTED;
>   }
>   
>   static int z_erofs_get_extent_decompressedlen(struct z_erofs_maprecorder *m)
> @@ -386,9 +375,7 @@ static int z_erofs_get_extent_decompressedlen(struct z_erofs_maprecorder *m)
>   				m->delta[1] = 1;
>   				DBG_BUGON(1);
>   			}
> -		} else if (m->type == Z_EROFS_LCLUSTER_TYPE_PLAIN ||
> -			   m->type == Z_EROFS_LCLUSTER_TYPE_HEAD1 ||
> -			   m->type == Z_EROFS_LCLUSTER_TYPE_HEAD2) {
> +		} else if (m->type < Z_EROFS_LCLUSTER_TYPE_MAX) {
>   			if (lcn != headlcn)
>   				break;	/* ends at the next HEAD lcluster */
>   			m->delta[1] = 1;
> @@ -452,8 +439,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
>   		}
>   		/* m.lcn should be >= 1 if endoff < m.clusterofs */
>   		if (!m.lcn) {
> -			erofs_err(inode->i_sb,
> -				  "invalid logical cluster 0 at nid %llu",
> +			erofs_err(inode->i_sb, "invalid logical cluster 0 at nid %llu",
>   				  vi->nid);
>   			err = -EFSCORRUPTED;
>   			goto unmap_out;
> @@ -469,8 +455,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
>   			goto unmap_out;
>   		break;
>   	default:
> -		erofs_err(inode->i_sb,
> -			  "unknown type %u @ offset %llu of nid %llu",
> +		erofs_err(inode->i_sb, "unknown type %u @ offset %llu of nid %llu",
>   			  m.type, ofs, vi->nid);
>   		err = -EOPNOTSUPP;
>   		goto unmap_out;