[PATCH 0/3] tmpfs: Casefold fixes

[PATCH 0/3] tmpfs: Casefold fixes

[André Almeida]

After casefold support for tmpfs was merged into vfs tree, two warnings
were reported and I also found a small fix in the code.

Thanks Nathan Chancellor and Stephen Rothwell!

André Almeida (3):
  libfs: Fix kernel-doc warning in generic_ci_validate_strict_name
  tmpfs: Fix type for sysfs' casefold attribute
  tmpfs: Initialize sysfs during tmpfs init

 include/linux/fs.h |  10 ++---
 mm/shmem.c         | 105 +++++++++++++++++++++++++++++----------------
 2 files changed, 73 insertions(+), 42 deletions(-)

-- 
2.47.0

[PATCH 1/3] libfs: Fix kernel-doc warning in generic_ci_validate_strict_name

[André Almeida]

Fix the indentation of the return values from
generic_ci_validate_strict_name() to properly render the comment and to
address a `make htmldocs` warning:

Documentation/filesystems/api-summary:14: include/linux/fs.h:3504:
WARNING: Bullet list ends without a blank line; unexpected unindent.

Fixes: 0e152beb5aa1 ("libfs: Create the helper function generic_ci_validate_strict_name()")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/lkml/20241030162435.05425f60@canb.auug.org.au/
Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 include/linux/fs.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3b279f60e48f..b562a161e2ee 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3499,12 +3499,12 @@ int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
  * @name: name of the new file
  *
  * Return:
- * * True if the filename is suitable for this directory. It can be
- * true if a given name is not suitable for a strict encoding
- * directory, but the directory being used isn't strict
+ * * True: if the filename is suitable for this directory. It can be
+ *   true if a given name is not suitable for a strict encoding
+ *   directory, but the directory being used isn't strict
  * * False if the filename isn't suitable for this directory. This only
- * happens when a directory is casefolded and the filesystem is strict
- * about its encoding.
+ *   happens when a directory is casefolded and the filesystem is strict
+ *   about its encoding.
  */
 static inline bool generic_ci_validate_strict_name(struct inode *dir, struct qstr *name)
 {
-- 
2.47.0

[PATCH 2/3] tmpfs: Fix type for sysfs' casefold attribute

[André Almeida]

DEVICE_STRING_ATTR_RO should be only used by device drivers since it
relies on `struct device` to use device_show_string() function. Using
this with non device code led to a kCFI violation:

> cat /sys/fs/tmpfs/features/casefold
[   70.558496] CFI failure at kobj_attr_show+0x2c/0x4c (target: device_show_string+0x0/0x38; expected type: 0xc527b809)

Like the other filesystems, fix this by manually declaring the attribute
using kobj_attribute() and writing a proper show() function.

Also, leave macros for anyone that need to expand tmpfs sysfs' with
more attributes (as seen in fs/btrfs/sysfs.c).

Fixes: 5132f08bd332 ("tmpfs: Expose filesystem features via sysfs")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/lkml/20241031051822.GA2947788@thelio-3990X/
Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 mm/shmem.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index b86f526a1cb1..6038e1d11987 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5548,13 +5548,38 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
 
 #if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
+
+#define __INIT_KOBJ_ATTR(_name, _mode, _show, _store)			\
+{									\
+	.attr	= { .name = __stringify(_name), .mode = _mode },	\
+	.show	= _show,						\
+	.store	= _store,						\
+}
+
+#define TMPFS_ATTR_W(_name, _store)				\
+	static struct kobj_attribute tmpfs_attr_##_name =	\
+			__INIT_KOBJ_ATTR(_name, 0200, NULL, _store)
+
+#define TMPFS_ATTR_RW(_name, _show, _store)			\
+	static struct kobj_attribute tmpfs_attr_##_name =	\
+			__INIT_KOBJ_ATTR(_name, 0644, _show, _store)
+
+#define TMPFS_ATTR_RO(_name, _show)				\
+	static struct kobj_attribute tmpfs_attr_##_name =	\
+			__INIT_KOBJ_ATTR(_name, 0444, _show, NULL)
+
 #if IS_ENABLED(CONFIG_UNICODE)
-static DEVICE_STRING_ATTR_RO(casefold, 0444, "supported");
+static ssize_t casefold_show(struct kobject *kobj, struct kobj_attribute *a,
+			char *buf)
+{
+		return sysfs_emit(buf, "supported\n");
+}
+TMPFS_ATTR_RO(casefold, casefold_show);
 #endif
 
 static struct attribute *tmpfs_attributes[] = {
 #if IS_ENABLED(CONFIG_UNICODE)
-	&dev_attr_casefold.attr.attr,
+	&tmpfs_attr_casefold.attr,
 #endif
 	NULL
 };
-- 
2.47.0

Re: [PATCH 2/3] tmpfs: Fix type for sysfs' casefold attribute

[Nathan Chancellor]

On Thu, Oct 31, 2024 at 10:37:40PM -0300, André Almeida wrote:
> DEVICE_STRING_ATTR_RO should be only used by device drivers since it
> relies on `struct device` to use device_show_string() function. Using
> this with non device code led to a kCFI violation:
> 
> > cat /sys/fs/tmpfs/features/casefold
> [   70.558496] CFI failure at kobj_attr_show+0x2c/0x4c (target: device_show_string+0x0/0x38; expected type: 0xc527b809)
> 
> Like the other filesystems, fix this by manually declaring the attribute
> using kobj_attribute() and writing a proper show() function.
> 
> Also, leave macros for anyone that need to expand tmpfs sysfs' with
> more attributes (as seen in fs/btrfs/sysfs.c).
> 
> Fixes: 5132f08bd332 ("tmpfs: Expose filesystem features via sysfs")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://lore.kernel.org/lkml/20241031051822.GA2947788@thelio-3990X/
> Signed-off-by: André Almeida <andrealmeid@igalia.com>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>

> ---
>  mm/shmem.c | 29 +++++++++++++++++++++++++++--
>  1 file changed, 27 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index b86f526a1cb1..6038e1d11987 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -5548,13 +5548,38 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
>  EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
>  
>  #if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
> +
> +#define __INIT_KOBJ_ATTR(_name, _mode, _show, _store)			\
> +{									\
> +	.attr	= { .name = __stringify(_name), .mode = _mode },	\
> +	.show	= _show,						\
> +	.store	= _store,						\
> +}
> +
> +#define TMPFS_ATTR_W(_name, _store)				\
> +	static struct kobj_attribute tmpfs_attr_##_name =	\
> +			__INIT_KOBJ_ATTR(_name, 0200, NULL, _store)
> +
> +#define TMPFS_ATTR_RW(_name, _show, _store)			\
> +	static struct kobj_attribute tmpfs_attr_##_name =	\
> +			__INIT_KOBJ_ATTR(_name, 0644, _show, _store)
> +
> +#define TMPFS_ATTR_RO(_name, _show)				\
> +	static struct kobj_attribute tmpfs_attr_##_name =	\
> +			__INIT_KOBJ_ATTR(_name, 0444, _show, NULL)
> +
>  #if IS_ENABLED(CONFIG_UNICODE)
> -static DEVICE_STRING_ATTR_RO(casefold, 0444, "supported");
> +static ssize_t casefold_show(struct kobject *kobj, struct kobj_attribute *a,
> +			char *buf)
> +{
> +		return sysfs_emit(buf, "supported\n");

Small nit, I think this might be overindented?

> +}
> +TMPFS_ATTR_RO(casefold, casefold_show);
>  #endif
>  
>  static struct attribute *tmpfs_attributes[] = {
>  #if IS_ENABLED(CONFIG_UNICODE)
> -	&dev_attr_casefold.attr.attr,
> +	&tmpfs_attr_casefold.attr,
>  #endif
>  	NULL
>  };
> -- 
> 2.47.0
> 

[PATCH 3/3] tmpfs: Initialize sysfs during tmpfs init

[André Almeida]

Instead of using fs_initcall(), initialize sysfs with the rest of the
filesystem. This is the right way to do it because otherwise any error
during tmpfs_sysfs_init() would get silently ignored. It's also useful
if tmpfs' sysfs ever need to display runtime information.

Signed-off-by: André Almeida <andrealmeid@igalia.com>
---
 mm/shmem.c | 130 ++++++++++++++++++++++++++++-------------------------
 1 file changed, 68 insertions(+), 62 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 6038e1d11987..8ff2f619f531 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5126,6 +5126,66 @@ static struct file_system_type shmem_fs_type = {
 	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP | FS_MGTIME,
 };
 
+#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
+
+#define __INIT_KOBJ_ATTR(_name, _mode, _show, _store)			\
+{									\
+	.attr	= { .name = __stringify(_name), .mode = _mode },	\
+	.show	= _show,						\
+	.store	= _store,						\
+}
+
+#define TMPFS_ATTR_W(_name, _store)				\
+	static struct kobj_attribute tmpfs_attr_##_name =	\
+			__INIT_KOBJ_ATTR(_name, 0200, NULL, _store)
+
+#define TMPFS_ATTR_RW(_name, _show, _store)			\
+	static struct kobj_attribute tmpfs_attr_##_name =	\
+			__INIT_KOBJ_ATTR(_name, 0644, _show, _store)
+
+#define TMPFS_ATTR_RO(_name, _show)				\
+	static struct kobj_attribute tmpfs_attr_##_name =	\
+			__INIT_KOBJ_ATTR(_name, 0444, _show, NULL)
+
+#if IS_ENABLED(CONFIG_UNICODE)
+static ssize_t casefold_show(struct kobject *kobj, struct kobj_attribute *a,
+			char *buf)
+{
+		return sysfs_emit(buf, "supported\n");
+}
+TMPFS_ATTR_RO(casefold, casefold_show);
+#endif
+
+static struct attribute *tmpfs_attributes[] = {
+#if IS_ENABLED(CONFIG_UNICODE)
+	&tmpfs_attr_casefold.attr,
+#endif
+	NULL
+};
+
+static const struct attribute_group tmpfs_attribute_group = {
+	.attrs = tmpfs_attributes,
+	.name = "features"
+};
+
+static struct kobject *tmpfs_kobj;
+
+static int __init tmpfs_sysfs_init(void)
+{
+	int ret;
+
+	tmpfs_kobj = kobject_create_and_add("tmpfs", fs_kobj);
+	if (!tmpfs_kobj)
+		return -ENOMEM;
+
+	ret = sysfs_create_group(tmpfs_kobj, &tmpfs_attribute_group);
+	if (ret)
+		kobject_put(tmpfs_kobj);
+
+	return ret;
+}
+#endif /* CONFIG_SYSFS && CONFIG_TMPFS */
+
 void __init shmem_init(void)
 {
 	int error;
@@ -5149,6 +5209,14 @@ void __init shmem_init(void)
 		goto out1;
 	}
 
+#ifdef CONFIG_SYSFS
+	error = tmpfs_sysfs_init();
+	if (error) {
+		pr_err("Could not init tmpfs sysfs\n");
+		goto out1;
+	}
+#endif
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY)
 		SHMEM_SB(shm_mnt->mnt_sb)->huge = shmem_huge;
@@ -5546,65 +5614,3 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 	return page;
 }
 EXPORT_SYMBOL_GPL(shmem_read_mapping_page_gfp);
-
-#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
-
-#define __INIT_KOBJ_ATTR(_name, _mode, _show, _store)			\
-{									\
-	.attr	= { .name = __stringify(_name), .mode = _mode },	\
-	.show	= _show,						\
-	.store	= _store,						\
-}
-
-#define TMPFS_ATTR_W(_name, _store)				\
-	static struct kobj_attribute tmpfs_attr_##_name =	\
-			__INIT_KOBJ_ATTR(_name, 0200, NULL, _store)
-
-#define TMPFS_ATTR_RW(_name, _show, _store)			\
-	static struct kobj_attribute tmpfs_attr_##_name =	\
-			__INIT_KOBJ_ATTR(_name, 0644, _show, _store)
-
-#define TMPFS_ATTR_RO(_name, _show)				\
-	static struct kobj_attribute tmpfs_attr_##_name =	\
-			__INIT_KOBJ_ATTR(_name, 0444, _show, NULL)
-
-#if IS_ENABLED(CONFIG_UNICODE)
-static ssize_t casefold_show(struct kobject *kobj, struct kobj_attribute *a,
-			char *buf)
-{
-		return sysfs_emit(buf, "supported\n");
-}
-TMPFS_ATTR_RO(casefold, casefold_show);
-#endif
-
-static struct attribute *tmpfs_attributes[] = {
-#if IS_ENABLED(CONFIG_UNICODE)
-	&tmpfs_attr_casefold.attr,
-#endif
-	NULL
-};
-
-static const struct attribute_group tmpfs_attribute_group = {
-	.attrs = tmpfs_attributes,
-	.name = "features"
-};
-
-static struct kobject *tmpfs_kobj;
-
-static int __init tmpfs_sysfs_init(void)
-{
-	int ret;
-
-	tmpfs_kobj = kobject_create_and_add("tmpfs", fs_kobj);
-	if (!tmpfs_kobj)
-		return -ENOMEM;
-
-	ret = sysfs_create_group(tmpfs_kobj, &tmpfs_attribute_group);
-	if (ret)
-		kobject_put(tmpfs_kobj);
-
-	return ret;
-}
-
-fs_initcall(tmpfs_sysfs_init);
-#endif /* CONFIG_SYSFS && CONFIG_TMPFS */
-- 
2.47.0

Re: [PATCH 3/3] tmpfs: Initialize sysfs during tmpfs init

[Nathan Chancellor]

Hi André,

On Thu, Oct 31, 2024 at 10:37:41PM -0300, André Almeida wrote:
> Instead of using fs_initcall(), initialize sysfs with the rest of the
> filesystem. This is the right way to do it because otherwise any error
> during tmpfs_sysfs_init() would get silently ignored. It's also useful
> if tmpfs' sysfs ever need to display runtime information.
> 
> Signed-off-by: André Almeida <andrealmeid@igalia.com>
> ---
>  mm/shmem.c | 130 ++++++++++++++++++++++++++++-------------------------
>  1 file changed, 68 insertions(+), 62 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 6038e1d11987..8ff2f619f531 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -5126,6 +5126,66 @@ static struct file_system_type shmem_fs_type = {
>  	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP | FS_MGTIME,
>  };
>  
> +#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)

This condition...

> +static int __init tmpfs_sysfs_init(void)
> +{
> +	int ret;
> +
> +	tmpfs_kobj = kobject_create_and_add("tmpfs", fs_kobj);
> +	if (!tmpfs_kobj)
> +		return -ENOMEM;
> +
> +	ret = sysfs_create_group(tmpfs_kobj, &tmpfs_attribute_group);
> +	if (ret)
> +		kobject_put(tmpfs_kobj);
> +
> +	return ret;
> +}
> +#endif /* CONFIG_SYSFS && CONFIG_TMPFS */
> +
>  void __init shmem_init(void)
>  {
>  	int error;
> @@ -5149,6 +5209,14 @@ void __init shmem_init(void)
>  		goto out1;
>  	}
>  
> +#ifdef CONFIG_SYSFS

and this condition are not the same, so there will be a compile error if
CONFIG_SHMEM and CONFIG_SYSFS are enabled but CONFIG_TMPFS is not, such
as with ARCH=x86_64 allnoconfig for me:

  mm/shmem.c: In function 'shmem_init':
  mm/shmem.c:5243:17: error: implicit declaration of function 'tmpfs_sysfs_init'; did you mean 'uids_sysfs_init'? [-Wimplicit-function-declaration]
   5243 |         error = tmpfs_sysfs_init();
        |                 ^~~~~~~~~~~~~~~~
        |                 uids_sysfs_init

> +	error = tmpfs_sysfs_init();
> +	if (error) {
> +		pr_err("Could not init tmpfs sysfs\n");
> +		goto out1;
> +	}
> +#endif

Cheers,
Nathan

Re: [PATCH 3/3] tmpfs: Initialize sysfs during tmpfs init

[André Almeida]

Em 01/11/2024 04:19, Nathan Chancellor escreveu:
> Hi André,
> 
> On Thu, Oct 31, 2024 at 10:37:41PM -0300, André Almeida wrote:
>> Instead of using fs_initcall(), initialize sysfs with the rest of the
>> filesystem. This is the right way to do it because otherwise any error
>> during tmpfs_sysfs_init() would get silently ignored. It's also useful
>> if tmpfs' sysfs ever need to display runtime information.
>>
>> Signed-off-by: André Almeida <andrealmeid@igalia.com>
>> ---
>>   mm/shmem.c | 130 ++++++++++++++++++++++++++++-------------------------
>>   1 file changed, 68 insertions(+), 62 deletions(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 6038e1d11987..8ff2f619f531 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -5126,6 +5126,66 @@ static struct file_system_type shmem_fs_type = {
>>   	.fs_flags	= FS_USERNS_MOUNT | FS_ALLOW_IDMAP | FS_MGTIME,
>>   };
>>   
>> +#if defined(CONFIG_SYSFS) && defined(CONFIG_TMPFS)
> 
> This condition...
> 
>> +static int __init tmpfs_sysfs_init(void)
>> +{
>> +	int ret;
>> +
>> +	tmpfs_kobj = kobject_create_and_add("tmpfs", fs_kobj);
>> +	if (!tmpfs_kobj)
>> +		return -ENOMEM;
>> +
>> +	ret = sysfs_create_group(tmpfs_kobj, &tmpfs_attribute_group);
>> +	if (ret)
>> +		kobject_put(tmpfs_kobj);
>> +
>> +	return ret;
>> +}
>> +#endif /* CONFIG_SYSFS && CONFIG_TMPFS */
>> +
>>   void __init shmem_init(void)
>>   {
>>   	int error;
>> @@ -5149,6 +5209,14 @@ void __init shmem_init(void)
>>   		goto out1;
>>   	}
>>   
>> +#ifdef CONFIG_SYSFS
> 
> and this condition are not the same, so there will be a compile error if
> CONFIG_SHMEM and CONFIG_SYSFS are enabled but CONFIG_TMPFS is not, such
> as with ARCH=x86_64 allnoconfig for me:
> 
>    mm/shmem.c: In function 'shmem_init':
>    mm/shmem.c:5243:17: error: implicit declaration of function 'tmpfs_sysfs_init'; did you mean 'uids_sysfs_init'? [-Wimplicit-function-declaration]
>     5243 |         error = tmpfs_sysfs_init();
>          |                 ^~~~~~~~~~~~~~~~
>          |                 uids_sysfs_init
> 

Thanks for the catch! Fixed for v2

>> +	error = tmpfs_sysfs_init();
>> +	if (error) {
>> +		pr_err("Could not init tmpfs sysfs\n");
>> +		goto out1;
>> +	}
>> +#endif
> 
> Cheers,
> Nathan