linux-kernel - Re: [PATCH v5] erofs: use Z_EROFS_LCLUSTER_TYPE

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Message-ID: <04050888-7abf-40fa-98d6-6215b8ba989e@kernel.org>
Date: Mon, 17 Mar 2025 14:03:30 +0800
From: Chao Yu <chao@...nel.org>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: chao@...nel.org, linux-kernel@...r.kernel.org,
 Hongzhen Luo <hongzhen@...ux.alibaba.com>,
 linux-erofs mailing list <linux-erofs@...ts.ozlabs.org>
Subject: Re: [PATCH v5] erofs: use Z_EROFS_LCLUSTER_TYPE_MAX to simplify
 switches

On 3/17/25 01:17, Gao Xiang wrote:
> Hi Chao,
> 
> On 2025/3/16 10:36, Chao Yu wrote:
>> On 2025/2/10 11:29, Hongzhen Luo wrote:
>>> There's no need to enumerate each type.  No logic changes.
>>>
>>> Signed-off-by: Hongzhen Luo <hongzhen@...ux.alibaba.com>
>>
>> Looks good to me, feel free to add:
>>
>> Reviewed-by: Chao Yu <chao@...nel.org>
>>
>> And one minor comment below.
>>
>>> diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
>>> index 689437e99a5a..d278ebd60281 100644
>>> --- a/fs/erofs/zmap.c
>>> +++ b/fs/erofs/zmap.c
>>> @@ -265,26 +265,22 @@ 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_MAX) {
>>> +            erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
>>> +                  m->type, lcn, vi->nid);
>>> +            DBG_BUGON(1);
>>> +            return -EOPNOTSUPP;
>>  > +        } else if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {>               lookback_distance = m->delta[0];
>>>               if (!lookback_distance)
>>> -                goto err_bogus;
>>> +                break;
>>>               continue;
>>> -        case Z_EROFS_LCLUSTER_TYPE_PLAIN:
>>> -        case Z_EROFS_LCLUSTER_TYPE_HEAD1:
>>> -        case Z_EROFS_LCLUSTER_TYPE_HEAD2:
>>> +        } else {
>>>               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;
>>
>> Should return EFSCORRUPTED here? is m->type >= Z_EROFS_LCLUSTER_TYPE_MAX a possible
>> case?
> 
> It's impossible by the latest on-disk definition, see:
> #define Z_EROFS_LI_LCLUSTER_TYPE_MASK    (Z_EROFS_LCLUSTER_TYPE_MAX - 1)
> 
> Previously, it was useful before Z_EROFS_LCLUSTER_TYPE_HEAD2 was
> introduced, but the `default:` case is already deadcode now.

Xiang, thanks for the explanation.

So seems it can happen when mounting last image w/ old kernel which can not
support newly introduced Z_EROFS_LCLUSTER_TYPE_* type, then it makes sense to
return EOPNOTSUPP.

> 
>>
>> Btw, we'd better to do sanity check for m->type in z_erofs_load_full_lcluster(),
>> then we can treat m->type as reliable variable later.
>>
>>      advise = le16_to_cpu(di->di_advise);
>>      m->type = advise & Z_EROFS_LI_LCLUSTER_TYPE_MASK;
>>      if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
> 
> It's always false here.

So, what do you think of this?

>From af584b2eacd468f145e9ee31ccdeedb7355d5afd Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@...nel.org>
Date: Mon, 17 Mar 2025 13:57:55 +0800
Subject: [PATCH] erofs: remove dead codes for cleanup

z_erofs_extent_lookback() and z_erofs_get_extent_decompressedlen() tries
to do sanity check on m->type, however their caller z_erofs_map_blocks_fo()
has already checked that, so let's remove those dead codes.

Signed-off-by: Chao Yu <chao@...nel.org>
---
 fs/erofs/zmap.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index 8de50df05dfe..4d883ec212d7 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -265,17 +265,12 @@ static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,
 		if (err)
 			return err;

-		if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
-			erofs_err(sb, "unknown type %u @ lcn %lu of nid %llu",
-				  m->type, lcn, vi->nid);
-			DBG_BUGON(1);
-			return -EOPNOTSUPP;
-		} else if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {
+		if (m->type == Z_EROFS_LCLUSTER_TYPE_NONHEAD) {
 			lookback_distance = m->delta[0];
 			if (!lookback_distance)
 				break;
 			continue;
-		} else {
+		} else if (m->type < Z_EROFS_LCLUSTER_TYPE_MAX) {
 			m->headtype = m->type;
 			m->map->m_la = (lcn << lclusterbits) | m->clusterofs;
 			return 0;
@@ -379,11 +374,6 @@ static int z_erofs_get_extent_decompressedlen(struct z_erofs_maprecorder *m)
 			if (lcn != headlcn)
 				break;	/* ends at the next HEAD lcluster */
 			m->delta[1] = 1;
-		} else {
-			erofs_err(inode->i_sb, "unknown type %u @ lcn %llu of nid %llu",
-				  m->type, lcn, vi->nid);
-			DBG_BUGON(1);
-			return -EOPNOTSUPP;
 		}
 		lcn += m->delta[1];
 	}
-- 
2.48.1

> 
> Thanks,
> Gao Xiang
>