linux-kernel - Re: [PATCH v3 RESEND] f2fs: introduce sb.required

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Date:   Wed, 31 Jul 2019 21:22:15 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Chao Yu <chao@...nel.org>, linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 RESEND] f2fs: introduce sb.required_features to store
 incompatible features

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@...wei.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@...wei.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

> 
> 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
> > .
> >