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Date:   Thu, 1 Aug 2019 15:35:09 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     Chao Yu <chao@kernel.org>, linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 RESEND] f2fs: introduce sb.required_features to store
 incompatible features
Message-ID: <20190801223509.GB27597@jaegeuk-macbookpro.roam.corp.google.com>
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>
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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

> 
> 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
> >>> .
> >>>
> > .
> >