From: Hongzhen Luo <hongzhen@linux.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@linux.alibaba.com>
Signed-off-by: Hongbo Li <lihongbo22@huawei.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..b71f2a8074fe 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 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;
 
 	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;
+
+		newpfx = krealloc(pf->prefix,
+			sizeof(*newpfx) + pf->infix_len + 1, GFP_KERNEL);
+		if (newpfx) {
+			newpfx->infix[pf->infix_len] = '\0';
+			pf->prefix = newpfx;
+		} else {
+			ret = -ENOMEM;
+		}
+	}
 	sbi->xattr_prefixes = pfs;
 	if (ret)
 		erofs_xattr_prefixes_cleanup(sb);
-- 
2.22.0

Hi Hongbo,

kernel test robot noticed the following build errors:

[auto build test ERROR on xiang-erofs/dev-test]
[also build test ERROR on xiang-erofs/dev xiang-erofs/fixes brauner-vfs/vfs.all linus/master v6.19-rc2 next-20251219]
[cannot apply to mszeredi-fuse/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Hongbo-Li/iomap-stash-iomap-read-ctx-in-the-private-field-of-iomap_iter/20251224-122950
base:   https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git dev-test
patch link:    https://lore.kernel.org/r/20251224040932.496478-6-lihongbo22%40huawei.com
patch subject: [PATCH v11 05/10] erofs: support user-defined fingerprint name
config: powerpc-randconfig-001-20251225 (https://download.01.org/0day-ci/archive/20251225/202512251143.WPBiiQZA-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 4ef602d446057dabf5f61fb221669ecbeda49279)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251225/202512251143.WPBiiQZA-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512251143.WPBiiQZA-lkp@intel.com/

All errors (new ones prefixed by >>):

>> fs/erofs/super.c:302:8: error: no member named 'ishare_xattr_pfx' in 'struct erofs_sb_info'
     302 |                 sbi->ishare_xattr_pfx =
         |                 ~~~  ^
   1 error generated.


vim +302 fs/erofs/super.c

   263	
   264	static int erofs_read_superblock(struct super_block *sb)
   265	{
   266		struct erofs_sb_info *sbi = EROFS_SB(sb);
   267		struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
   268		struct erofs_super_block *dsb;
   269		void *data;
   270		int ret;
   271	
   272		data = erofs_read_metabuf(&buf, sb, 0, false);
   273		if (IS_ERR(data)) {
   274			erofs_err(sb, "cannot read erofs superblock");
   275			return PTR_ERR(data);
   276		}
   277	
   278		dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
   279		ret = -EINVAL;
   280		if (le32_to_cpu(dsb->magic) != EROFS_SUPER_MAGIC_V1) {
   281			erofs_err(sb, "cannot find valid erofs superblock");
   282			goto out;
   283		}
   284	
   285		sbi->blkszbits = dsb->blkszbits;
   286		if (sbi->blkszbits < 9 || sbi->blkszbits > PAGE_SHIFT) {
   287			erofs_err(sb, "blkszbits %u isn't supported", sbi->blkszbits);
   288			goto out;
   289		}
   290		if (dsb->dirblkbits) {
   291			erofs_err(sb, "dirblkbits %u isn't supported", dsb->dirblkbits);
   292			goto out;
   293		}
   294	
   295		sbi->feature_compat = le32_to_cpu(dsb->feature_compat);
   296		if (erofs_sb_has_sb_chksum(sbi)) {
   297			ret = erofs_superblock_csum_verify(sb, data);
   298			if (ret)
   299				goto out;
   300		}
   301		if (erofs_sb_has_ishare_xattrs(sbi))
 > 302			sbi->ishare_xattr_pfx =
   303				dsb->ishare_xattr_prefix_id & EROFS_XATTR_LONG_PREFIX_MASK;
   304	
   305		ret = -EINVAL;
   306		sbi->feature_incompat = le32_to_cpu(dsb->feature_incompat);
   307		if (sbi->feature_incompat & ~EROFS_ALL_FEATURE_INCOMPAT) {
   308			erofs_err(sb, "unidentified incompatible feature %x, please upgrade kernel",
   309				  sbi->feature_incompat & ~EROFS_ALL_FEATURE_INCOMPAT);
   310			goto out;
   311		}
   312	
   313		sbi->sb_size = 128 + dsb->sb_extslots * EROFS_SB_EXTSLOT_SIZE;
   314		if (sbi->sb_size > PAGE_SIZE - EROFS_SUPER_OFFSET) {
   315			erofs_err(sb, "invalid sb_extslots %u (more than a fs block)",
   316				  sbi->sb_size);
   317			goto out;
   318		}
   319		sbi->dif0.blocks = le32_to_cpu(dsb->blocks_lo);
   320		sbi->meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
   321	#ifdef CONFIG_EROFS_FS_XATTR
   322		sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
   323		sbi->xattr_prefix_start = le32_to_cpu(dsb->xattr_prefix_start);
   324		sbi->xattr_prefix_count = dsb->xattr_prefix_count;
   325		sbi->xattr_filter_reserved = dsb->xattr_filter_reserved;
   326	#endif
   327		sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
   328		if (erofs_sb_has_48bit(sbi) && dsb->rootnid_8b) {
   329			sbi->root_nid = le64_to_cpu(dsb->rootnid_8b);
   330			sbi->dif0.blocks = sbi->dif0.blocks |
   331					((u64)le16_to_cpu(dsb->rb.blocks_hi) << 32);
   332		} else {
   333			sbi->root_nid = le16_to_cpu(dsb->rb.rootnid_2b);
   334		}
   335		sbi->packed_nid = le64_to_cpu(dsb->packed_nid);
   336		if (erofs_sb_has_metabox(sbi)) {
   337			if (sbi->sb_size <= offsetof(struct erofs_super_block,
   338						     metabox_nid))
   339				return -EFSCORRUPTED;
   340			sbi->metabox_nid = le64_to_cpu(dsb->metabox_nid);
   341			if (sbi->metabox_nid & BIT_ULL(EROFS_DIRENT_NID_METABOX_BIT))
   342				return -EFSCORRUPTED;	/* self-loop detection */
   343		}
   344		sbi->inos = le64_to_cpu(dsb->inos);
   345	
   346		sbi->epoch = (s64)le64_to_cpu(dsb->epoch);
   347		sbi->fixed_nsec = le32_to_cpu(dsb->fixed_nsec);
   348		super_set_uuid(sb, (void *)dsb->uuid, sizeof(dsb->uuid));
   349	
   350		if (dsb->volume_name[0]) {
   351			sbi->volume_name = kstrndup(dsb->volume_name,
   352						    sizeof(dsb->volume_name), GFP_KERNEL);
   353			if (!sbi->volume_name)
   354				return -ENOMEM;
   355		}
   356	
   357		/* parse on-disk compression configurations */
   358		ret = z_erofs_parse_cfgs(sb, dsb);
   359		if (ret < 0)
   360			goto out;
   361	
   362		ret = erofs_scan_devices(sb, dsb);
   363	
   364		if (erofs_sb_has_48bit(sbi))
   365			erofs_info(sb, "EXPERIMENTAL 48-bit layout support in use. Use at your own risk!");
   366		if (erofs_sb_has_metabox(sbi))
   367			erofs_info(sb, "EXPERIMENTAL metadata compression support in use. Use at your own risk!");
   368		if (erofs_is_fscache_mode(sb))
   369			erofs_info(sb, "[deprecated] fscache-based on-demand read feature in use. Use at your own risk!");
   370	out:
   371		erofs_put_metabuf(&buf);
   372		return ret;
   373	}
   374	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

On 2025/12/25 12:08, kernel test robot wrote:
> Hi Hongbo,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on xiang-erofs/dev-test]
> [also build test ERROR on xiang-erofs/dev xiang-erofs/fixes brauner-vfs/vfs.all linus/master v6.19-rc2 next-20251219]
> [cannot apply to mszeredi-fuse/for-next]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Hongbo-Li/iomap-stash-iomap-read-ctx-in-the-private-field-of-iomap_iter/20251224-122950
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git dev-test
> patch link:    https://lore.kernel.org/r/20251224040932.496478-6-lihongbo22%40huawei.com
> patch subject: [PATCH v11 05/10] erofs: support user-defined fingerprint name
> config: powerpc-randconfig-001-20251225 (https://download.01.org/0day-ci/archive/20251225/202512251143.WPBiiQZA-lkp@intel.com/config)
> compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 4ef602d446057dabf5f61fb221669ecbeda49279)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251225/202512251143.WPBiiQZA-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202512251143.WPBiiQZA-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>>> fs/erofs/super.c:302:8: error: no member named 'ishare_xattr_pfx' in 'struct erofs_sb_info'
>       302 |                 sbi->ishare_xattr_pfx =
>           |                 ~~~  ^
>     1 error generated.
> 
> 
> vim +302 fs/erofs/super.c
> 
>     263	
>     264	static int erofs_read_superblock(struct super_block *sb)
>     265	{
>     266		struct erofs_sb_info *sbi = EROFS_SB(sb);
>     267		struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
>     268		struct erofs_super_block *dsb;
>     269		void *data;
>     270		int ret;
>     271	
>     272		data = erofs_read_metabuf(&buf, sb, 0, false);
>     273		if (IS_ERR(data)) {
>     274			erofs_err(sb, "cannot read erofs superblock");
>     275			return PTR_ERR(data);
>     276		}
>     277	
>     278		dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
>     279		ret = -EINVAL;
>     280		if (le32_to_cpu(dsb->magic) != EROFS_SUPER_MAGIC_V1) {
>     281			erofs_err(sb, "cannot find valid erofs superblock");
>     282			goto out;
>     283		}
>     284	
>     285		sbi->blkszbits = dsb->blkszbits;
>     286		if (sbi->blkszbits < 9 || sbi->blkszbits > PAGE_SHIFT) {
>     287			erofs_err(sb, "blkszbits %u isn't supported", sbi->blkszbits);
>     288			goto out;
>     289		}
>     290		if (dsb->dirblkbits) {
>     291			erofs_err(sb, "dirblkbits %u isn't supported", dsb->dirblkbits);
>     292			goto out;
>     293		}
>     294	
>     295		sbi->feature_compat = le32_to_cpu(dsb->feature_compat);
>     296		if (erofs_sb_has_sb_chksum(sbi)) {
>     297			ret = erofs_superblock_csum_verify(sb, data);
>     298			if (ret)
>     299				goto out;
>     300		}
>     301		if (erofs_sb_has_ishare_xattrs(sbi))
>   > 302			sbi->ishare_xattr_pfx =
>     303				dsb->ishare_xattr_prefix_id & EROFS_XATTR_LONG_PREFIX_MASK;
>     304	
>     305		ret = -EINVAL;
>     306		sbi->feature_incompat = le32_to_cpu(dsb->feature_incompat);
>     307		if (sbi->feature_incompat & ~EROFS_ALL_FEATURE_INCOMPAT) {
>     308			erofs_err(sb, "unidentified incompatible feature %x, please upgrade kernel",
>     309				  sbi->feature_incompat & ~EROFS_ALL_FEATURE_INCOMPAT);
>     310			goto out;
>     311		}
>     312	
>     313		sbi->sb_size = 128 + dsb->sb_extslots * EROFS_SB_EXTSLOT_SIZE;
>     314		if (sbi->sb_size > PAGE_SIZE - EROFS_SUPER_OFFSET) {
>     315			erofs_err(sb, "invalid sb_extslots %u (more than a fs block)",
>     316				  sbi->sb_size);
>     317			goto out;
>     318		}
>     319		sbi->dif0.blocks = le32_to_cpu(dsb->blocks_lo);
>     320		sbi->meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
>     321	#ifdef CONFIG_EROFS_FS_XATTR

The EROFS_FS_XATTR is disabled, so should put in here.. I will fix it in 
next version.

Thanks,
Hongbo

>     322		sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
>     323		sbi->xattr_prefix_start = le32_to_cpu(dsb->xattr_prefix_start);
>     324		sbi->xattr_prefix_count = dsb->xattr_prefix_count;
>     325		sbi->xattr_filter_reserved = dsb->xattr_filter_reserved;
>     326	#endif
>     327		sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
>     328		if (erofs_sb_has_48bit(sbi) && dsb->rootnid_8b) {
>     329			sbi->root_nid = le64_to_cpu(dsb->rootnid_8b);
>     330			sbi->dif0.blocks = sbi->dif0.blocks |
>     331					((u64)le16_to_cpu(dsb->rb.blocks_hi) << 32);
>     332		} else {
>     333			sbi->root_nid = le16_to_cpu(dsb->rb.rootnid_2b);
>     334		}
>     335		sbi->packed_nid = le64_to_cpu(dsb->packed_nid);
>     336		if (erofs_sb_has_metabox(sbi)) {
>     337			if (sbi->sb_size <= offsetof(struct erofs_super_block,
>     338						     metabox_nid))
>     339				return -EFSCORRUPTED;
>     340			sbi->metabox_nid = le64_to_cpu(dsb->metabox_nid);
>     341			if (sbi->metabox_nid & BIT_ULL(EROFS_DIRENT_NID_METABOX_BIT))
>     342				return -EFSCORRUPTED;	/* self-loop detection */
>     343		}
>     344		sbi->inos = le64_to_cpu(dsb->inos);
>     345	
>     346		sbi->epoch = (s64)le64_to_cpu(dsb->epoch);
>     347		sbi->fixed_nsec = le32_to_cpu(dsb->fixed_nsec);
>     348		super_set_uuid(sb, (void *)dsb->uuid, sizeof(dsb->uuid));
>     349	
>     350		if (dsb->volume_name[0]) {
>     351			sbi->volume_name = kstrndup(dsb->volume_name,
>     352						    sizeof(dsb->volume_name), GFP_KERNEL);
>     353			if (!sbi->volume_name)
>     354				return -ENOMEM;
>     355		}
>     356	
>     357		/* parse on-disk compression configurations */
>     358		ret = z_erofs_parse_cfgs(sb, dsb);
>     359		if (ret < 0)
>     360			goto out;
>     361	
>     362		ret = erofs_scan_devices(sb, dsb);
>     363	
>     364		if (erofs_sb_has_48bit(sbi))
>     365			erofs_info(sb, "EXPERIMENTAL 48-bit layout support in use. Use at your own risk!");
>     366		if (erofs_sb_has_metabox(sbi))
>     367			erofs_info(sb, "EXPERIMENTAL metadata compression support in use. Use at your own risk!");
>     368		if (erofs_is_fscache_mode(sb))
>     369			erofs_info(sb, "[deprecated] fscache-based on-demand read feature in use. Use at your own risk!");
>     370	out:
>     371		erofs_put_metabuf(&buf);
>     372		return ret;
>     373	}
>     374	
>

Hi Hongbo,

kernel test robot noticed the following build errors:

[auto build test ERROR on xiang-erofs/dev-test]
[also build test ERROR on xiang-erofs/dev xiang-erofs/fixes brauner-vfs/vfs.all linus/master v6.19-rc2 next-20251219]
[cannot apply to mszeredi-fuse/for-next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Hongbo-Li/iomap-stash-iomap-read-ctx-in-the-private-field-of-iomap_iter/20251224-122950
base:   https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git dev-test
patch link:    https://lore.kernel.org/r/20251224040932.496478-6-lihongbo22%40huawei.com
patch subject: [PATCH v11 05/10] erofs: support user-defined fingerprint name
config: nios2-randconfig-r071-20251225 (https://download.01.org/0day-ci/archive/20251225/202512251005.yZVSPUOm-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 11.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251225/202512251005.yZVSPUOm-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512251005.yZVSPUOm-lkp@intel.com/

All errors (new ones prefixed by >>):

   fs/erofs/super.c: In function 'erofs_read_superblock':
>> fs/erofs/super.c:302:20: error: 'struct erofs_sb_info' has no member named 'ishare_xattr_pfx'
     302 |                 sbi->ishare_xattr_pfx =
         |                    ^~

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for CAN_DEV
   Depends on [n]: NETDEVICES [=n] && CAN [=m]
   Selected by [m]:
   - CAN [=m] && NET [=y]


vim +302 fs/erofs/super.c

   263	
   264	static int erofs_read_superblock(struct super_block *sb)
   265	{
   266		struct erofs_sb_info *sbi = EROFS_SB(sb);
   267		struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
   268		struct erofs_super_block *dsb;
   269		void *data;
   270		int ret;
   271	
   272		data = erofs_read_metabuf(&buf, sb, 0, false);
   273		if (IS_ERR(data)) {
   274			erofs_err(sb, "cannot read erofs superblock");
   275			return PTR_ERR(data);
   276		}
   277	
   278		dsb = (struct erofs_super_block *)(data + EROFS_SUPER_OFFSET);
   279		ret = -EINVAL;
   280		if (le32_to_cpu(dsb->magic) != EROFS_SUPER_MAGIC_V1) {
   281			erofs_err(sb, "cannot find valid erofs superblock");
   282			goto out;
   283		}
   284	
   285		sbi->blkszbits = dsb->blkszbits;
   286		if (sbi->blkszbits < 9 || sbi->blkszbits > PAGE_SHIFT) {
   287			erofs_err(sb, "blkszbits %u isn't supported", sbi->blkszbits);
   288			goto out;
   289		}
   290		if (dsb->dirblkbits) {
   291			erofs_err(sb, "dirblkbits %u isn't supported", dsb->dirblkbits);
   292			goto out;
   293		}
   294	
   295		sbi->feature_compat = le32_to_cpu(dsb->feature_compat);
   296		if (erofs_sb_has_sb_chksum(sbi)) {
   297			ret = erofs_superblock_csum_verify(sb, data);
   298			if (ret)
   299				goto out;
   300		}
   301		if (erofs_sb_has_ishare_xattrs(sbi))
 > 302			sbi->ishare_xattr_pfx =
   303				dsb->ishare_xattr_prefix_id & EROFS_XATTR_LONG_PREFIX_MASK;
   304	
   305		ret = -EINVAL;
   306		sbi->feature_incompat = le32_to_cpu(dsb->feature_incompat);
   307		if (sbi->feature_incompat & ~EROFS_ALL_FEATURE_INCOMPAT) {
   308			erofs_err(sb, "unidentified incompatible feature %x, please upgrade kernel",
   309				  sbi->feature_incompat & ~EROFS_ALL_FEATURE_INCOMPAT);
   310			goto out;
   311		}
   312	
   313		sbi->sb_size = 128 + dsb->sb_extslots * EROFS_SB_EXTSLOT_SIZE;
   314		if (sbi->sb_size > PAGE_SIZE - EROFS_SUPER_OFFSET) {
   315			erofs_err(sb, "invalid sb_extslots %u (more than a fs block)",
   316				  sbi->sb_size);
   317			goto out;
   318		}
   319		sbi->dif0.blocks = le32_to_cpu(dsb->blocks_lo);
   320		sbi->meta_blkaddr = le32_to_cpu(dsb->meta_blkaddr);
   321	#ifdef CONFIG_EROFS_FS_XATTR
   322		sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
   323		sbi->xattr_prefix_start = le32_to_cpu(dsb->xattr_prefix_start);
   324		sbi->xattr_prefix_count = dsb->xattr_prefix_count;
   325		sbi->xattr_filter_reserved = dsb->xattr_filter_reserved;
   326	#endif
   327		sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
   328		if (erofs_sb_has_48bit(sbi) && dsb->rootnid_8b) {
   329			sbi->root_nid = le64_to_cpu(dsb->rootnid_8b);
   330			sbi->dif0.blocks = sbi->dif0.blocks |
   331					((u64)le16_to_cpu(dsb->rb.blocks_hi) << 32);
   332		} else {
   333			sbi->root_nid = le16_to_cpu(dsb->rb.rootnid_2b);
   334		}
   335		sbi->packed_nid = le64_to_cpu(dsb->packed_nid);
   336		if (erofs_sb_has_metabox(sbi)) {
   337			if (sbi->sb_size <= offsetof(struct erofs_super_block,
   338						     metabox_nid))
   339				return -EFSCORRUPTED;
   340			sbi->metabox_nid = le64_to_cpu(dsb->metabox_nid);
   341			if (sbi->metabox_nid & BIT_ULL(EROFS_DIRENT_NID_METABOX_BIT))
   342				return -EFSCORRUPTED;	/* self-loop detection */
   343		}
   344		sbi->inos = le64_to_cpu(dsb->inos);
   345	
   346		sbi->epoch = (s64)le64_to_cpu(dsb->epoch);
   347		sbi->fixed_nsec = le32_to_cpu(dsb->fixed_nsec);
   348		super_set_uuid(sb, (void *)dsb->uuid, sizeof(dsb->uuid));
   349	
   350		if (dsb->volume_name[0]) {
   351			sbi->volume_name = kstrndup(dsb->volume_name,
   352						    sizeof(dsb->volume_name), GFP_KERNEL);
   353			if (!sbi->volume_name)
   354				return -ENOMEM;
   355		}
   356	
   357		/* parse on-disk compression configurations */
   358		ret = z_erofs_parse_cfgs(sb, dsb);
   359		if (ret < 0)
   360			goto out;
   361	
   362		ret = erofs_scan_devices(sb, dsb);
   363	
   364		if (erofs_sb_has_48bit(sbi))
   365			erofs_info(sb, "EXPERIMENTAL 48-bit layout support in use. Use at your own risk!");
   366		if (erofs_sb_has_metabox(sbi))
   367			erofs_info(sb, "EXPERIMENTAL metadata compression support in use. Use at your own risk!");
   368		if (erofs_is_fscache_mode(sb))
   369			erofs_info(sb, "[deprecated] fscache-based on-demand read feature in use. Use at your own risk!");
   370	out:
   371		erofs_put_metabuf(&buf);
   372		return ret;
   373	}
   374	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

On 2025/12/24 12:09, Hongbo Li wrote:
> From: Hongzhen Luo <hongzhen@linux.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@linux.alibaba.com>
> Signed-off-by: Hongbo Li <lihongbo22@huawei.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..b71f2a8074fe 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 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;

Could we use the same naming as `ishare_xattr_prefix_id`?

>   	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;

It seems this part is still unmodified.

But after checking the code just now, I agree it may need more work
in order to pass dsb to erofs_xattr_prefixes_init(), so I can live
with the current status.

Thanks,
Gao Xiang

>   
>   	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;
> +
> +		newpfx = krealloc(pf->prefix,
> +			sizeof(*newpfx) + pf->infix_len + 1, GFP_KERNEL);
> +		if (newpfx) {
> +			newpfx->infix[pf->infix_len] = '\0';
> +			pf->prefix = newpfx;
> +		} else {
> +			ret = -ENOMEM;
> +		}
> +	}
>   	sbi->xattr_prefixes = pfs;
>   	if (ret)
>   		erofs_xattr_prefixes_cleanup(sb);