linux-kernel - Re: [PATCH v10 05/10] erofs: support user-defined fingerprint name

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Message-ID: <9f03647d-2996-4d16-8c64-5afecdc904a9@linux.alibaba.com>
Date: Tue, 23 Dec 2025 15:22:00 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Hongbo Li <lihongbo22@...wei.com>
Cc: linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, Chao Yu <chao@...nel.org>,
 Christian Brauner <brauner@...nel.org>, "Darrick J. Wong"
 <djwong@...nel.org>, Amir Goldstein <amir73il@...il.com>,
 Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v10 05/10] erofs: support user-defined fingerprint name



On 2025/12/23 09:56, Hongbo Li wrote:
> From: Hongzhen Luo <hongzhen@...ux.alibaba.com>
> 
> When creating the EROFS image, users can specify the fingerprint name.
> This is to prepare for the upcoming inode page cache share.
> 
> Signed-off-by: Hongzhen Luo <hongzhen@...ux.alibaba.com>
> Signed-off-by: Hongbo Li <lihongbo22@...wei.com>
> ---
>   fs/erofs/Kconfig    |  9 +++++++++
>   fs/erofs/erofs_fs.h |  5 +++--
>   fs/erofs/internal.h |  2 ++
>   fs/erofs/super.c    |  3 +++
>   fs/erofs/xattr.c    | 13 +++++++++++++
>   5 files changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index d81f3318417d..c88b6d0714a4 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -194,3 +194,12 @@ config EROFS_FS_PCPU_KTHREAD_HIPRI
>   	  at higher priority.
>   
>   	  If unsure, say N.
> +
> +config EROFS_FS_PAGE_CACHE_SHARE
> +	bool "EROFS page cache share support (experimental)"
> +	depends on EROFS_FS && EROFS_FS_XATTR && !EROFS_FS_ONDEMAND
> +	help
> +	  This enables page cache sharing among inodes with identical
> +	  content fingerprints on the same device.

`on the same device` seems ambiguous because of `device`.

maybe just `on the same machine`.

> +
> +	  If unsure, say N.
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index e24268acdd62..20515d2462af 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -17,7 +17,7 @@
>   #define EROFS_FEATURE_COMPAT_XATTR_FILTER		0x00000004
>   #define EROFS_FEATURE_COMPAT_SHARED_EA_IN_METABOX	0x00000008
>   #define EROFS_FEATURE_COMPAT_PLAIN_XATTR_PFX		0x00000010
> -
> +#define EROFS_FEATURE_COMPAT_ISHARE_XATTRS		0x00000020
>   
>   /*
>    * Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
> @@ -83,7 +83,8 @@ struct erofs_super_block {
>   	__le32 xattr_prefix_start;	/* start of long xattr prefixes */
>   	__le64 packed_nid;	/* nid of the special packed inode */
>   	__u8 xattr_filter_reserved; /* reserved for xattr name filter */
> -	__u8 reserved[3];
> +	__u8 ishare_xattr_prefix_id;	/* indexes the ishare key in prefix xattres */
> +	__u8 reserved[2];
>   	__le32 build_time;	/* seconds added to epoch for mkfs time */
>   	__le64 rootnid_8b;	/* (48BIT on) nid of root directory */
>   	__le64 reserved2;
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 98fe652aea33..99e2857173c3 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -134,6 +134,7 @@ struct erofs_sb_info {
>   	u32 xattr_blkaddr;
>   	u32 xattr_prefix_start;
>   	u8 xattr_prefix_count;
> +	u8 ishare_xattr_pfx;
>   	struct erofs_xattr_prefix_item *xattr_prefixes;
>   	unsigned int xattr_filter_reserved;
>   #endif
> @@ -238,6 +239,7 @@ EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
>   EROFS_FEATURE_FUNCS(xattr_filter, compat, COMPAT_XATTR_FILTER)
>   EROFS_FEATURE_FUNCS(shared_ea_in_metabox, compat, COMPAT_SHARED_EA_IN_METABOX)
>   EROFS_FEATURE_FUNCS(plain_xattr_pfx, compat, COMPAT_PLAIN_XATTR_PFX)
> +EROFS_FEATURE_FUNCS(ishare_xattrs, compat, COMPAT_ISHARE_XATTRS)
>   
>   static inline u64 erofs_nid_to_ino64(struct erofs_sb_info *sbi, erofs_nid_t nid)
>   {
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 2a44c4e5af4f..68480f10e69d 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -298,6 +298,9 @@ static int erofs_read_superblock(struct super_block *sb)
>   		if (ret)
>   			goto out;
>   	}
> +	if (erofs_sb_has_ishare_xattrs(sbi))
> +		sbi->ishare_xattr_pfx =
> +			dsb->ishare_xattr_prefix_id & EROFS_XATTR_LONG_PREFIX_MASK;

Is it possible to move this one into erofs_xattr_prefixes_init()?

we could pass dsb into erofs_xattr_prefixes_init() too.

>   
>   	ret = -EINVAL;
>   	sbi->feature_incompat = le32_to_cpu(dsb->feature_incompat);
> diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
> index 396536d9a862..969e77efd038 100644
> --- a/fs/erofs/xattr.c
> +++ b/fs/erofs/xattr.c
> @@ -519,6 +519,19 @@ int erofs_xattr_prefixes_init(struct super_block *sb)
>   	}
>   
>   	erofs_put_metabuf(&buf);
> +	if (!ret && erofs_sb_has_ishare_xattrs(sbi)) {
> +		struct erofs_xattr_prefix_item *pf = pfs + sbi->ishare_xattr_pfx;
> +		struct erofs_xattr_long_prefix *newpfx;

then:
		sbi->ishare_xattr_pfx =
			dsb->ishare_xattr_prefix_id & EROFS_XATTR_LONG_PREFIX_MASK;
...

Thanks,
Gao Xiang