[PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Jingbo Xu]

Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.

Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
Cc: <stable@vger.kernel.org> # 6.4+
Reviewed-by: Gao Xiang <xiang@kernel.org>
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
changes since v2:
- add Reviewed-by tag (Gao Xiang)
- update list in Documentation/ABI/testing/sysfs-fs-erofs
(https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
---
 Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
 fs/erofs/sysfs.c                         | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-fs-erofs b/Documentation/ABI/testing/sysfs-fs-erofs
index e4cf6fc6a106..0b8b4354e40b 100644
--- a/Documentation/ABI/testing/sysfs-fs-erofs
+++ b/Documentation/ABI/testing/sysfs-fs-erofs
@@ -5,7 +5,7 @@ Description:	Shows all enabled kernel features.
 		Supported features:
 		compr_cfgs, big_pcluster, chunked_file, device_table,
 		compr_head2, sb_chksum, ztailpacking, dedupe, fragments,
-		48bit, metabox.
+		xattr_prefixes, 48bit, metabox.
 
 What:		/sys/fs/erofs/<disk>/sync_decompress
 Date:		November 2021
diff --git a/fs/erofs/sysfs.c b/fs/erofs/sysfs.c
index 6734483a440f..dfcec9376cd5 100644
--- a/fs/erofs/sysfs.c
+++ b/fs/erofs/sysfs.c
@@ -95,6 +95,7 @@ EROFS_ATTR_FEATURE(sb_chksum);
 EROFS_ATTR_FEATURE(ztailpacking);
 EROFS_ATTR_FEATURE(fragments);
 EROFS_ATTR_FEATURE(dedupe);
+EROFS_ATTR_FEATURE(xattr_prefixes);
 EROFS_ATTR_FEATURE(48bit);
 EROFS_ATTR_FEATURE(metabox);
 
@@ -108,6 +109,7 @@ static struct attribute *erofs_feat_attrs[] = {
 	ATTR_LIST(ztailpacking),
 	ATTR_LIST(fragments),
 	ATTR_LIST(dedupe),
+	ATTR_LIST(xattr_prefixes),
 	ATTR_LIST(48bit),
 	ATTR_LIST(metabox),
 	NULL,
-- 
2.19.1.6.gb485710b

Re: [PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Greg KH]

On Wed, Sep 02, 2026 at 09:50:39AM +0800, Jingbo Xu wrote:
> Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
> supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.
> 
> Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
> Cc: <stable@vger.kernel.org> # 6.4+
> Reviewed-by: Gao Xiang <xiang@kernel.org>
> Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> ---
> changes since v2:
> - add Reviewed-by tag (Gao Xiang)
> - update list in Documentation/ABI/testing/sysfs-fs-erofs
> (https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
> ---
>  Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
>  fs/erofs/sysfs.c                         | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)

Why is adding a new feature a stable thing?

confused,

greg k-h

Re: [PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Gao Xiang]

Hi Greg,

On Wed, Sep 02, 2026 at 07:36:13AM +0200, Greg KH wrote:
> On Wed, Sep 02, 2026 at 09:50:39AM +0800, Jingbo Xu wrote:
> > Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
> > supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.
> > 
> > Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
> > Cc: <stable@vger.kernel.org> # 6.4+
> > Reviewed-by: Gao Xiang <xiang@kernel.org>
> > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > ---
> > changes since v2:
> > - add Reviewed-by tag (Gao Xiang)
> > - update list in Documentation/ABI/testing/sysfs-fs-erofs
> > (https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
> > ---
> >  Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
> >  fs/erofs/sysfs.c                         | 2 ++
> >  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> Why is adding a new feature a stable thing?

It's not a new feature (Also, this patch has 3 lines diff):
This is a bugfix to address the missing part of
commit 6a318ccd7e08 ("erofs: enable long extended
attribute name prefixes"") since every on-disk features
should be shown in `/sys/fs/erofs/features/*` according to
the definition of:

What:           /sys/fs/erofs/features/
Date:           November 2021
Contact:        "Huang Jianan" <huangjianan@oppo.com>
Description:    Shows all enabled kernel features.
...

IOWs, this sysfs entry should be part of commit 6a318ccd7e08
to indicate this feature is supported since Linux 6.4+

Thanks,
Gao Xiang

> 
> confused,
> 
> greg k-h
> 

Re: [PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Greg KH]

On Wed, Sep 02, 2026 at 06:53:16PM +0800, Gao Xiang wrote:
> Hi Greg,
> 
> On Wed, Sep 02, 2026 at 07:36:13AM +0200, Greg KH wrote:
> > On Wed, Sep 02, 2026 at 09:50:39AM +0800, Jingbo Xu wrote:
> > > Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
> > > supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.
> > > 
> > > Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
> > > Cc: <stable@vger.kernel.org> # 6.4+
> > > Reviewed-by: Gao Xiang <xiang@kernel.org>
> > > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > > ---
> > > changes since v2:
> > > - add Reviewed-by tag (Gao Xiang)
> > > - update list in Documentation/ABI/testing/sysfs-fs-erofs
> > > (https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
> > > ---
> > >  Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
> > >  fs/erofs/sysfs.c                         | 2 ++
> > >  2 files changed, 3 insertions(+), 1 deletion(-)
> > 
> > Why is adding a new feature a stable thing?
> 
> It's not a new feature (Also, this patch has 3 lines diff):
> This is a bugfix to address the missing part of
> commit 6a318ccd7e08 ("erofs: enable long extended
> attribute name prefixes"") since every on-disk features
> should be shown in `/sys/fs/erofs/features/*` according to
> the definition of:
> 
> What:           /sys/fs/erofs/features/
> Date:           November 2021
> Contact:        "Huang Jianan" <huangjianan@oppo.com>
> Description:    Shows all enabled kernel features.
> ...
> 
> IOWs, this sysfs entry should be part of commit 6a318ccd7e08
> to indicate this feature is supported since Linux 6.4+

Ok, but as this has not been present for a very long time, did anyone
even notice and need this now in stable kernels?  :)

thanks,

greg k-h

Re: [PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Gao Xiang]

On Wed, Sep 02, 2026 at 01:38:16PM +0200, Greg KH wrote:
> On Wed, Sep 02, 2026 at 06:53:16PM +0800, Gao Xiang wrote:
> > Hi Greg,
> > 
> > On Wed, Sep 02, 2026 at 07:36:13AM +0200, Greg KH wrote:
> > > On Wed, Sep 02, 2026 at 09:50:39AM +0800, Jingbo Xu wrote:
> > > > Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
> > > > supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.
> > > > 
> > > > Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
> > > > Cc: <stable@vger.kernel.org> # 6.4+
> > > > Reviewed-by: Gao Xiang <xiang@kernel.org>
> > > > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > > > ---
> > > > changes since v2:
> > > > - add Reviewed-by tag (Gao Xiang)
> > > > - update list in Documentation/ABI/testing/sysfs-fs-erofs
> > > > (https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
> > > > ---
> > > >  Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
> > > >  fs/erofs/sysfs.c                         | 2 ++
> > > >  2 files changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > Why is adding a new feature a stable thing?
> > 
> > It's not a new feature (Also, this patch has 3 lines diff):
> > This is a bugfix to address the missing part of
> > commit 6a318ccd7e08 ("erofs: enable long extended
> > attribute name prefixes"") since every on-disk features
> > should be shown in `/sys/fs/erofs/features/*` according to
> > the definition of:
> > 
> > What:           /sys/fs/erofs/features/
> > Date:           November 2021
> > Contact:        "Huang Jianan" <huangjianan@oppo.com>
> > Description:    Shows all enabled kernel features.
> > ...
> > 
> > IOWs, this sysfs entry should be part of commit 6a318ccd7e08
> > to indicate this feature is supported since Linux 6.4+
> 
> Ok, but as this has not been present for a very long time, did anyone
> even notice and need this now in stable kernels?  :)

I think Jingbo needs it (btw, I'm no longer in Alibaba Cloud
anymore).

Also it would be better to port this into stable kernels so
that users can get the supported on-disk features in a more
unique obvious way.

Thanks,
Gao Xiang

> 
> thanks,
> 
> greg k-h
> 

Re: [PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Greg KH]

On Wed, Sep 02, 2026 at 07:42:36PM +0800, Gao Xiang wrote:
> On Wed, Sep 02, 2026 at 01:38:16PM +0200, Greg KH wrote:
> > On Wed, Sep 02, 2026 at 06:53:16PM +0800, Gao Xiang wrote:
> > > Hi Greg,
> > > 
> > > On Wed, Sep 02, 2026 at 07:36:13AM +0200, Greg KH wrote:
> > > > On Wed, Sep 02, 2026 at 09:50:39AM +0800, Jingbo Xu wrote:
> > > > > Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
> > > > > supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.
> > > > > 
> > > > > Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
> > > > > Cc: <stable@vger.kernel.org> # 6.4+
> > > > > Reviewed-by: Gao Xiang <xiang@kernel.org>
> > > > > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > > > > ---
> > > > > changes since v2:
> > > > > - add Reviewed-by tag (Gao Xiang)
> > > > > - update list in Documentation/ABI/testing/sysfs-fs-erofs
> > > > > (https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
> > > > > ---
> > > > >  Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
> > > > >  fs/erofs/sysfs.c                         | 2 ++
> > > > >  2 files changed, 3 insertions(+), 1 deletion(-)
> > > > 
> > > > Why is adding a new feature a stable thing?
> > > 
> > > It's not a new feature (Also, this patch has 3 lines diff):
> > > This is a bugfix to address the missing part of
> > > commit 6a318ccd7e08 ("erofs: enable long extended
> > > attribute name prefixes"") since every on-disk features
> > > should be shown in `/sys/fs/erofs/features/*` according to
> > > the definition of:
> > > 
> > > What:           /sys/fs/erofs/features/
> > > Date:           November 2021
> > > Contact:        "Huang Jianan" <huangjianan@oppo.com>
> > > Description:    Shows all enabled kernel features.
> > > ...
> > > 
> > > IOWs, this sysfs entry should be part of commit 6a318ccd7e08
> > > to indicate this feature is supported since Linux 6.4+
> > 
> > Ok, but as this has not been present for a very long time, did anyone
> > even notice and need this now in stable kernels?  :)
> 
> I think Jingbo needs it (btw, I'm no longer in Alibaba Cloud
> anymore).
> 
> Also it would be better to port this into stable kernels so
> that users can get the supported on-disk features in a more
> unique obvious way.

Ok, that makes more sense, sorry for the noise!

greg k-h

Re: [PATCH v3] erofs: add sysfs feature entry for xattr prefixes

[Gao Xiang]

On Wed, Sep 02, 2026 at 01:54:08PM +0200, Greg KH wrote:
> On Wed, Sep 02, 2026 at 07:42:36PM +0800, Gao Xiang wrote:
> > On Wed, Sep 02, 2026 at 01:38:16PM +0200, Greg KH wrote:
> > > On Wed, Sep 02, 2026 at 06:53:16PM +0800, Gao Xiang wrote:
> > > > Hi Greg,
> > > > 
> > > > On Wed, Sep 02, 2026 at 07:36:13AM +0200, Greg KH wrote:
> > > > > On Wed, Sep 02, 2026 at 09:50:39AM +0800, Jingbo Xu wrote:
> > > > > > Let /sys/fs/erofs/features/xattr_prefixes advertise that this kernel
> > > > > > supports the EROFS_FEATURE_INCOMPAT_XATTR_PREFIXES on-disk format.
> > > > > > 
> > > > > > Fixes: 6a318ccd7e08 ("erofs: enable long extended attribute name prefixes")
> > > > > > Cc: <stable@vger.kernel.org> # 6.4+
> > > > > > Reviewed-by: Gao Xiang <xiang@kernel.org>
> > > > > > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
> > > > > > ---
> > > > > > changes since v2:
> > > > > > - add Reviewed-by tag (Gao Xiang)
> > > > > > - update list in Documentation/ABI/testing/sysfs-fs-erofs
> > > > > > (https://sashiko.dev/#/patchset/20260901062243.109172-1-jefflexu%40linux.alibaba.com)
> > > > > > ---
> > > > > >  Documentation/ABI/testing/sysfs-fs-erofs | 2 +-
> > > > > >  fs/erofs/sysfs.c                         | 2 ++
> > > > > >  2 files changed, 3 insertions(+), 1 deletion(-)
> > > > > 
> > > > > Why is adding a new feature a stable thing?
> > > > 
> > > > It's not a new feature (Also, this patch has 3 lines diff):
> > > > This is a bugfix to address the missing part of
> > > > commit 6a318ccd7e08 ("erofs: enable long extended
> > > > attribute name prefixes"") since every on-disk features
> > > > should be shown in `/sys/fs/erofs/features/*` according to
> > > > the definition of:
> > > > 
> > > > What:           /sys/fs/erofs/features/
> > > > Date:           November 2021
> > > > Contact:        "Huang Jianan" <huangjianan@oppo.com>
> > > > Description:    Shows all enabled kernel features.
> > > > ...
> > > > 
> > > > IOWs, this sysfs entry should be part of commit 6a318ccd7e08
> > > > to indicate this feature is supported since Linux 6.4+
> > > 
> > > Ok, but as this has not been present for a very long time, did anyone
> > > even notice and need this now in stable kernels?  :)
> > 
> > I think Jingbo needs it (btw, I'm no longer in Alibaba Cloud
> > anymore).
> > 
> > Also it would be better to port this into stable kernels so
> > that users can get the supported on-disk features in a more
> > unique obvious way.
> 
> Ok, that makes more sense, sorry for the noise!

Thanks for your suggestion and time too!

Thanks,
Gao Xiang

> 
> greg k-h
>