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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>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <345c55ea-01c2-a9d1-4367-716dbd08ae9d@huawei.com>
Date:   Thu, 1 Aug 2019 15:45:01 +0800
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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.

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
>>> .
>>>
> .
>