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Date:   Tue, 30 Jul 2019 16:18:50 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <chao@kernel.org>
Cc:     linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, Chao Yu <yuchao0@huawei.com>
Subject: Re: [PATCH v3 RESEND] f2fs: introduce sb.required_features to store
 incompatible features
Message-ID: <20190730231850.GA7097@jaegeuk-macbookpro.roam.corp.google.com>
References: <20190729150351.12223-1-chao@kernel.org>
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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;
	}


> +			~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