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Subject: Re: [PATCH v3 RESEND] f2fs: introduce sb.required_features to store
 incompatible features
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     Chao Yu <chao@kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>
References: <20190729150351.12223-1-chao@kernel.org>
 <20190730231850.GA7097@jaegeuk-macbookpro.roam.corp.google.com>
 <c7232d80-a4d8-88ae-2eca-01290dd0e56a@huawei.com>
 <20190801042215.GC84433@jaegeuk-macbookpro.roam.corp.google.com>
 <345c55ea-01c2-a9d1-4367-716dbd08ae9d@huawei.com>
 <20190801223509.GB27597@jaegeuk-macbookpro.roam.corp.google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <8e906ddb-81d8-b63e-0c19-1ee9fc7f5cbf@huawei.com>
Date:   Fri, 2 Aug 2019 15:54:00 +0800
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On 2019/8/2 6:35, Jaegeuk Kim wrote:
> On 08/01, Chao Yu wrote:
>> On 2019/8/1 12:22, Jaegeuk Kim wrote:
>>> On 07/31, Chao Yu wrote:
>>>> On 2019/7/31 7:18, Jaegeuk Kim wrote:
>>>>> On 07/29, Chao Yu wrote:
>>>>>> From: Chao Yu <yuchao0@huawei.com>
>>>>>>
>>>>>> Later after this patch was merged, all new incompatible feature's
>>>>>> bit should be added into sb.required_features field, and define new
>>>>>> feature function with F2FS_INCOMPAT_FEATURE_FUNCS() macro.
>>>>>>
>>>>>> Then during mount, we will do sanity check with enabled features in
>>>>>> image, if there are features in sb.required_features that kernel can
>>>>>> not recognize, just fail the mount.
>>>>>>
>>>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>>>> ---
>>>>>> v3:
>>>>>> - change commit title.
>>>>>> - fix wrong macro name.
>>>>>>  fs/f2fs/f2fs.h          | 15 +++++++++++++++
>>>>>>  fs/f2fs/super.c         | 10 ++++++++++
>>>>>>  include/linux/f2fs_fs.h |  3 ++-
>>>>>>  3 files changed, 27 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>>> index a6eb828af57f..b8e17d4ddb8d 100644
>>>>>> --- a/fs/f2fs/f2fs.h
>>>>>> +++ b/fs/f2fs/f2fs.h
>>>>>> @@ -163,6 +163,15 @@ struct f2fs_mount_info {
>>>>>>  #define F2FS_CLEAR_FEATURE(sbi, mask)					\
>>>>>>  	(sbi->raw_super->feature &= ~cpu_to_le32(mask))
>>>>>>  
>>>>>> +#define F2FS_INCOMPAT_FEATURES		0
>>>>>> +
>>>>>> +#define F2FS_HAS_INCOMPAT_FEATURE(sbi, mask)				\
>>>>>> +	((sbi->raw_super->required_features & cpu_to_le32(mask)) != 0)
>>>>>> +#define F2FS_SET_INCOMPAT_FEATURE(sbi, mask)				\
>>>>>> +	(sbi->raw_super->required_features |= cpu_to_le32(mask))
>>>>>> +#define F2FS_CLEAR_INCOMPAT_FEATURE(sbi, mask)				\
>>>>>> +	(sbi->raw_super->required_features &= ~cpu_to_le32(mask))
>>>>>> +
>>>>>>  /*
>>>>>>   * Default values for user and/or group using reserved blocks
>>>>>>   */
>>>>>> @@ -3585,6 +3594,12 @@ F2FS_FEATURE_FUNCS(lost_found, LOST_FOUND);
>>>>>>  F2FS_FEATURE_FUNCS(sb_chksum, SB_CHKSUM);
>>>>>>  F2FS_FEATURE_FUNCS(casefold, CASEFOLD);
>>>>>>  
>>>>>> +#define F2FS_INCOMPAT_FEATURE_FUNCS(name, flagname) \
>>>>>> +static inline int f2fs_sb_has_##name(struct f2fs_sb_info *sbi) \
>>>>>> +{ \
>>>>>> +	return F2FS_HAS_INCOMPAT_FEATURE(sbi, F2FS_FEATURE_##flagname); \
>>>>>> +}
>>>>>> +
>>>>>>  #ifdef CONFIG_BLK_DEV_ZONED
>>>>>>  static inline bool f2fs_blkz_is_seq(struct f2fs_sb_info *sbi, int devi,
>>>>>>  				    block_t blkaddr)
>>>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>>>> index 5540fee0fe3f..3701dcce90e6 100644
>>>>>> --- a/fs/f2fs/super.c
>>>>>> +++ b/fs/f2fs/super.c
>>>>>> @@ -2513,6 +2513,16 @@ static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
>>>>>>  		return -EINVAL;
>>>>>>  	}
>>>>>>  
>>>>>> +	/* check whether current kernel supports all features on image */
>>>>>> +	if (le32_to_cpu(raw_super->required_features) &
>>>>>
>>>>> ...
>>>>> #define F2FS_FEATURE_VERITY	0x0400	/* reserved */
>>>>> ...
>>>>> #define F2FS_FEATURE_CASEFOLD	0x1000
>>>>> #define F2FS_FEATURE_SUPPORT	0x1BFF
>>>>>
>>>>> 	if (le32_to_cpu(raw_super->required_features) & ~F2FS_FEATURE_SUPPORT) {
>>>>> 		...
>>>>> 		return -EINVAL;
>>>>> 	}
>>>>
>>>> Um, I thought .required_features are used to store new feature flags from 0x0.
>>>>
>>>> All 'F2FS_FEATURE_SUPPORT' bits should be stored in sb.feature instead of
>>>> sb.required_features, I'm confused...
>>>
>>> I'm thinking,
>>>
>>> f2fs-tools     sb->required_features     f2fs    F2FS_FEATURE_SUPPORT
>>> v0             0                         v0      no_check -> ok
>>> v1             0x1BFF                    v0      no_check -> ok
>>> v0             0                         v1      0x1BFF -> ok
>>> v1             0x1BFF                    v1      0x1BFF -> ok
>>> v2             0x3BFF                    v1      0x1BFF -> fail
>>> v1             0x1BFF                    v2      0x3BFF -> ok
>>> v2             0x3BFF                    v2      0x3BFF -> ok
>>
>> I see, it's a bit waste for 0x1FFF low bits in sb->required_features. Why not
>> leaving 0x0FFF in sb->feature w/o sanity check. And make all new incompatible
>> features (including casefold) adding into sb->required_features.
> 
> I don't think we can define like this, and we still have 32bits feature filed.
> This would give another confusion to understand. VERITY is reserved only now.
> 
> #define F2FS_FEATURE_CASEFOLD		0x0001

Oops, so you want to make .required_features being almost a mirror of .feature,
and do sanity check on it... I can see now. :P

If so, why not just use .feature:

kernel	tool
v5.2 .. 1.12
#define	F2FS_FEATURE_SUPPORT		0x0BFF

v5.3 .. 1.13
#define F2FS_FEATURE_CASEFOLD		0x1000
#define	F2FS_FEATURE_SUPPORT		0x1BFF

v5.4 .. 1.14
#define F2FS_FEATURE_CASEFOLD		0x1000
#define F2FS_FEATURE_COMPRESS		0x2000
#define	F2FS_FEATURE_SUPPORT		0x3BFF

f2fs-tools	sb->feature		f2fs	F2FS_FEATURE_SUPPORT

[enable all features in tools]
v1.12		0x0BFF			v5.2	no_check -> ok
v1.12		0x0BFF			v5.3	0x1BFF -> ok
v1.12		0x0BFF			v5.4	0x3BFF -> ok

v1.13		0x1BFF			v5.2	that's issue we need to fix
v1.13		0x1BFF			v5.3	0x1BFF -> ok
v1.13		0x1BFF			v5.4	0x3BFF -> ok

v1.14		0x3BFF			v5.2	that's issue we need to fix
v1.14		0x3BFF			v5.3	0x1BFF -> fail
v1.14		0x3BFF			v5.4	0x3BFF -> ok

Or am I missing something?

Thanks,

> 
>>
>> Then that would be:
>>
>> kernel	tool
>> v5.2 .. 1.12
>> #define	F2FS_FEATURE_SUPPORT		0x0000
>>
>> v5.3 .. 1.13
>> #define F2FS_FEATURE_CASEFOLD		0x0001
>> #define	F2FS_FEATURE_SUPPORT		0x0001
>>
>> v5.4 .. 1.14
>> #define F2FS_FEATURE_CASEFOLD		0x0001
>> #define F2FS_FEATURE_COMPRESS		0x0002
>> #define	F2FS_FEATURE_SUPPORT		0x0003
>>
>> f2fs-tools	sb->required_features	f2fs	F2FS_FEATURE_SUPPORT
>>
>> v1.12		0x0000			v5.2	no_check -> ok
>> v1.12		0x0000			v5.3	0x0001 -> ok
>> v1.12		0x0000			v5.4	0x0003 -> ok
>>
>> v1.13		0x0001			v5.2	that's issue we need to fix
>> v1.13		0x0001			v5.3	0x0001 -> ok
>> v1.13		0x0001			v5.4	0x0003 -> ok
>>
>> v1.14		0x0003			v5.2	that's issue we need to fix
>> v1.14		0x0003			v5.3	0x0001 -> fail
>> v1.14		0x0003			v5.4	0x0003 -> ok
>>
>> And all compatible features can be added into sb->feature[_VERITY, ....].
>>
>> Would that okay to you?
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>
>>>>>> +			~F2FS_INCOMPAT_FEATURES) {
>>>>>> +		f2fs_info(sbi, "Unsupported feature: %x: supported: %x",
>>>>>> +			  le32_to_cpu(raw_super->required_features) ^
>>>>>> +			  F2FS_INCOMPAT_FEATURES,
>>>>>> +			  F2FS_INCOMPAT_FEATURES);
>>>>>> +		return -EINVAL;
>>>>>> +	}
>>>>>> +
>>>>>>  	/* Check checksum_offset and crc in superblock */
>>>>>>  	if (__F2FS_HAS_FEATURE(raw_super, F2FS_FEATURE_SB_CHKSUM)) {
>>>>>>  		crc_offset = le32_to_cpu(raw_super->checksum_offset);
>>>>>> diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
>>>>>> index a2b36b2e286f..4141be3f219c 100644
>>>>>> --- a/include/linux/f2fs_fs.h
>>>>>> +++ b/include/linux/f2fs_fs.h
>>>>>> @@ -117,7 +117,8 @@ struct f2fs_super_block {
>>>>>>  	__u8 hot_ext_count;		/* # of hot file extension */
>>>>>>  	__le16	s_encoding;		/* Filename charset encoding */
>>>>>>  	__le16	s_encoding_flags;	/* Filename charset encoding flags */
>>>>>> -	__u8 reserved[306];		/* valid reserved region */
>>>>>> +	__le32 required_features;       /* incompatible features to old kernel */
>>>>>> +	__u8 reserved[302];		/* valid reserved region */
>>>>>>  	__le32 crc;			/* checksum of superblock */
>>>>>>  } __packed;
>>>>>>  
>>>>>> -- 
>>>>>> 2.22.0
>>>>> .
>>>>>
>>> .
>>>
> .
>