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Message-ID: <df86044f-b192-492a-99f2-bad019570f9d@huawei.com>
Date: Mon, 17 Nov 2025 15:41:54 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.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
Hi Xiang,
On 2025/11/17 10:54, Gao Xiang wrote:
>
>
> 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 for review, but here we should pass the char * to erofs_getxattr
to obtain the xattr length and value. And xattr_prefixes packed all
entries together so we cannot tranform
sbi->xattr_prefixes[sbi->ishare_xattr_pfx] into char * directly.
Thanks,
Hongbo
> 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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