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Message-ID: <a3b0bac9-d08f-44dc-8adb-7cc85cae7b13@linux.alibaba.com>
Date: Mon, 17 Nov 2025 10:54:57 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Hongbo Li <lihongbo22@...wei.com>, chao@...nel.org, brauner@...nel.org,
djwong@...nel.org, amir73il@...il.com, joannelkoong@...il.com
Cc: linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 4/9] erofs: support user-defined fingerprint name
On 2025/11/14 17:55, 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 | 6 ++++--
> fs/erofs/internal.h | 6 ++++++
> fs/erofs/super.c | 5 ++++-
> fs/erofs/xattr.c | 26 ++++++++++++++++++++++++++
> fs/erofs/xattr.h | 6 ++++++
> 6 files changed, 55 insertions(+), 3 deletions(-)
>
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index d81f3318417d..1b5c0cd99203 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_INODE_SHARE
> + bool "EROFS inode page cache share support (experimental)"
> + depends on EROFS_FS && EROFS_FS_XATTR && !EROFS_FS_ONDEMAND
> + help
> + This permits EROFS to share page cache for files with same
> + fingerprints.
I tend to use "EROFS_FS_PAGE_CACHE_SHARE" since it's closer to
user impact definition (inode sharing is ambiguious), but we
could leave "ishare.c" since it's closer to the implementation
details.
And how about:
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.
If unsure, say N.
> +
> + If unsure, say N.
> \ No newline at end of file
"\ No newline at end of file" should be fixed.
> diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h
> index 3d5738f80072..104518cd161d 100644
> --- a/fs/erofs/erofs_fs.h
> +++ b/fs/erofs/erofs_fs.h
> @@ -35,8 +35,9 @@
> #define EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES 0x00000040
> #define EROFS_FEATURE_INCOMPAT_48BIT 0x00000080
> #define EROFS_FEATURE_INCOMPAT_METABOX 0x00000100
> +#define EROFS_FEATURE_INCOMPAT_ISHARE_KEY 0x00000200
I do think it should be a compatible feature since images can be
mounted in the old kernels without any issue, and it should be
renamed as
EROFS_FEATURE_COMPAT_ISHARE_XATTRS
> #define EROFS_ALL_FEATURE_INCOMPAT \
> - ((EROFS_FEATURE_INCOMPAT_METABOX << 1) - 1)
> + ((EROFS_FEATURE_INCOMPAT_ISHARE_KEY << 1) - 1)
>
> #define EROFS_SB_EXTSLOT_SIZE 16
>
> @@ -83,7 +84,8 @@ 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_key_start; /* start of ishare key */
ishare_xattr_prefix_id; ?
> + __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 e80b35db18e4..3ebbb7c5d085 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -167,6 +167,11 @@ struct erofs_sb_info {
> struct erofs_domain *domain;
> char *fsid;
> char *domain_id;
> +
> + /* inode page cache share support */
> + u8 ishare_key_start;
u8 ishare_xattr_pfx;
> + u8 ishare_key_idx;
why need this, considering we could just use
sbi->xattr_prefixes[sbi->ishare_xattr_pfx]
to get this.
> + char *ishare_key;
> };
>
> #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
> @@ -236,6 +241,7 @@ EROFS_FEATURE_FUNCS(dedupe, incompat, INCOMPAT_DEDUPE)
> EROFS_FEATURE_FUNCS(xattr_prefixes, incompat, INCOMPAT_XATTR_PREFIXES)
> EROFS_FEATURE_FUNCS(48bit, incompat, INCOMPAT_48BIT)
> EROFS_FEATURE_FUNCS(metabox, incompat, INCOMPAT_METABOX)
> +EROFS_FEATURE_FUNCS(ishare_key, incompat, INCOMPAT_ISHARE_KEY)
> 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)
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 0d88c04684b9..3561473cb789 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -339,7 +339,7 @@ static int erofs_read_superblock(struct super_block *sb)
> return -EFSCORRUPTED; /* self-loop detection */
> }
> sbi->inos = le64_to_cpu(dsb->inos);
> -
> + sbi->ishare_key_start = dsb->ishare_key_start;
> sbi->epoch = (s64)le64_to_cpu(dsb->epoch);
> sbi->fixed_nsec = le32_to_cpu(dsb->fixed_nsec);
> super_set_uuid(sb, (void *)dsb->uuid, sizeof(dsb->uuid));
> @@ -738,6 +738,9 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
> if (err)
> return err;
>
> + err = erofs_xattr_set_ishare_key(sb);
I don't think it's necessary to duplicate the copy, just use
"sbi->xattr_prefixes[sbi->ishare_xattr_pfx]" directly.
Thanks,
Gao Xiang
> + if (err)
> + return err;
> erofs_set_sysfs_name(sb);
> err = erofs_register_sysfs(sb);
> if (err)
> diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
> index 396536d9a862..3c99091f39a5 100644
> --- a/fs/erofs/xattr.c
> +++ b/fs/erofs/xattr.c
> @@ -564,3 +564,29 @@ struct posix_acl *erofs_get_acl(struct inode *inode, int type, bool rcu)
> return acl;
> }
> #endif
> +
> +#ifdef CONFIG_EROFS_FS_INODE_SHARE
> +int erofs_xattr_set_ishare_key(struct super_block *sb)
> +{
> + struct erofs_sb_info *sbi = EROFS_SB(sb);
> + struct erofs_xattr_prefix_item *pf;
> + char *ishare_key;
> +
> + if (!sbi->xattr_prefixes ||
> + !(sbi->ishare_key_start & EROFS_XATTR_LONG_PREFIX))
> + return 0;
> +
> + pf = sbi->xattr_prefixes +
> + (sbi->ishare_key_start & EROFS_XATTR_LONG_PREFIX_MASK);
> + if (!pf || pf >= sbi->xattr_prefixes + sbi->xattr_prefix_count)
> + return 0;
> + ishare_key = kmalloc(pf->infix_len + 1, GFP_KERNEL);
> + if (!ishare_key)
> + return -ENOMEM;
> + memcpy(ishare_key, pf->prefix->infix, pf->infix_len);
> + ishare_key[pf->infix_len] = '\0';
> + sbi->ishare_key = ishare_key;
> + sbi->ishare_key_idx = pf->prefix->base_index;
> + return 0;
> +}
> +#endif
> diff --git a/fs/erofs/xattr.h b/fs/erofs/xattr.h
> index 6317caa8413e..21684359662c 100644
> --- a/fs/erofs/xattr.h
> +++ b/fs/erofs/xattr.h
> @@ -67,4 +67,10 @@ struct posix_acl *erofs_get_acl(struct inode *inode, int type, bool rcu);
> #define erofs_get_acl (NULL)
> #endif
>
> +#ifdef CONFIG_EROFS_FS_INODE_SHARE
> +int erofs_xattr_set_ishare_key(struct super_block *sb);
> +#else
> +static inline int erofs_xattr_set_ishare_key(struct super_block *sb) { return 0; }
> +#endif
> +
> #endif
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