Patchwork i2c: i2c-dev: Create 'name' attribute automatically

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Submitter Guenter Roeck
Date Aug. 31, 2013, 4:30 p.m.
Message ID <1377966619-20197-1-git-send-email-linux@roeck-us.net>
Download mbox | patch
Permalink /patch/271543/
State Deferred
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Comments

Guenter Roeck - Aug. 31, 2013, 4:30 p.m.
The 'name' attribute is needed for all i2c-dev class devices, meaning
it can be created automatically by pointing to it in the class data
structure. This simplifies the code and reduces the probability for race
conditions.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 drivers/i2c/i2c-dev.c |   32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)
Wolfram Sang - Sept. 25, 2013, 8:20 p.m.
On Sat, Aug 31, 2013 at 09:30:19AM -0700, Guenter Roeck wrote:
> The 'name' attribute is needed for all i2c-dev class devices, meaning
> it can be created automatically by pointing to it in the class data
> structure. This simplifies the code and reduces the probability for race
> conditions.

What race condition?

> 
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> ---
>  drivers/i2c/i2c-dev.c |   32 ++++++++++++++++----------------
>  1 file changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
> index c3ccdea..46eea02 100644
> --- a/drivers/i2c/i2c-dev.c
> +++ b/drivers/i2c/i2c-dev.c
> @@ -111,7 +111,11 @@ static ssize_t show_adapter_name(struct device *dev,
>  		return -ENODEV;
>  	return sprintf(buf, "%s\n", i2c_dev->adap->name);
>  }
> -static DEVICE_ATTR(name, S_IRUGO, show_adapter_name, NULL);
> +
> +static struct device_attribute i2c_dev_attributes[] = {
> +	__ATTR(name, S_IRUGO, show_adapter_name, NULL),
> +	{ }
> +};
>  
>  /* ------------------------------------------------------------------------- */
>  
> @@ -538,7 +542,11 @@ static const struct file_operations i2cdev_fops = {
>  
>  /* ------------------------------------------------------------------------- */
>  
> -static struct class *i2c_dev_class;
> +static struct class i2c_dev_class = {
> +	.owner = THIS_MODULE,
> +	.name = "i2c-dev",
> +	.dev_attrs = i2c_dev_attributes,
> +};

Have you tried this with two instances? I don't think it will work since
class_register modifies the class struct.

Regards,

   Wolfram
Guenter Roeck - Sept. 25, 2013, 9:11 p.m.
On Wed, Sep 25, 2013 at 10:20:35PM +0200, Wolfram Sang wrote:
> On Sat, Aug 31, 2013 at 09:30:19AM -0700, Guenter Roeck wrote:
> > The 'name' attribute is needed for all i2c-dev class devices, meaning
> > it can be created automatically by pointing to it in the class data
> > structure. This simplifies the code and reduces the probability for race
> > conditions.
> 
> What race condition?
> 

Userspace trying to access the name attribute before it is created.
See http://kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/
for details; Greg describes the problem and solution much better than I could
ever do.

> > 
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > ---
> >  drivers/i2c/i2c-dev.c |   32 ++++++++++++++++----------------
> >  1 file changed, 16 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
> > index c3ccdea..46eea02 100644
> > --- a/drivers/i2c/i2c-dev.c
> > +++ b/drivers/i2c/i2c-dev.c
> > @@ -111,7 +111,11 @@ static ssize_t show_adapter_name(struct device *dev,
> >  		return -ENODEV;
> >  	return sprintf(buf, "%s\n", i2c_dev->adap->name);
> >  }
> > -static DEVICE_ATTR(name, S_IRUGO, show_adapter_name, NULL);
> > +
> > +static struct device_attribute i2c_dev_attributes[] = {
> > +	__ATTR(name, S_IRUGO, show_adapter_name, NULL),
> > +	{ }
> > +};
> >  
> >  /* ------------------------------------------------------------------------- */
> >  
> > @@ -538,7 +542,11 @@ static const struct file_operations i2cdev_fops = {
> >  
> >  /* ------------------------------------------------------------------------- */
> >  
> > -static struct class *i2c_dev_class;
> > +static struct class i2c_dev_class = {
> > +	.owner = THIS_MODULE,
> > +	.name = "i2c-dev",
> > +	.dev_attrs = i2c_dev_attributes,
> > +};
> 
> Have you tried this with two instances? I don't think it will work since
> class_register modifies the class struct.
> 
Half a dozen instances, actually. Unless I am missing something, seems to be
unlikely that there is a problem, since the kernel would fail all over the place
if there was a problem with class->dev_attrs (or its replacement dev_groups);

Anyway, the patch is obsolete; one is supposed to use class->dev_groups now.

Thanks,
Guenter
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Wolfram Sang - Sept. 26, 2013, 8:28 a.m.
Hi,

> > What race condition?
> > 
> 
> Userspace trying to access the name attribute before it is created.
> See http://kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/

Thanks!

> > Have you tried this with two instances? I don't think it will work since
> > class_register modifies the class struct.
> > 
> Half a dozen instances, actually. Unless I am missing something, seems to be

My bad. Sorry for the noise.

> Anyway, the patch is obsolete; one is supposed to use class->dev_groups now.

Are you willing to update the patch?

Thanks,

   Wolfram
Guenter Roeck - Sept. 26, 2013, 10:37 a.m.
On 09/26/2013 01:28 AM, Wolfram Sang wrote:
> Hi,
>
>>> What race condition?
>>>
>>
>> Userspace trying to access the name attribute before it is created.
>> See http://kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/
>
> Thanks!
>
>>> Have you tried this with two instances? I don't think it will work since
>>> class_register modifies the class struct.
>>>
>> Half a dozen instances, actually. Unless I am missing something, seems to be
>
> My bad. Sorry for the noise.
>
>> Anyway, the patch is obsolete; one is supposed to use class->dev_groups now.
>
> Are you willing to update the patch?
>

Sure. Give me a couple of days.

Thanks,
Guenter


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Patch

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index c3ccdea..46eea02 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -111,7 +111,11 @@  static ssize_t show_adapter_name(struct device *dev,
 		return -ENODEV;
 	return sprintf(buf, "%s\n", i2c_dev->adap->name);
 }
-static DEVICE_ATTR(name, S_IRUGO, show_adapter_name, NULL);
+
+static struct device_attribute i2c_dev_attributes[] = {
+	__ATTR(name, S_IRUGO, show_adapter_name, NULL),
+	{ }
+};
 
 /* ------------------------------------------------------------------------- */
 
@@ -538,7 +542,11 @@  static const struct file_operations i2cdev_fops = {
 
 /* ------------------------------------------------------------------------- */
 
-static struct class *i2c_dev_class;
+static struct class i2c_dev_class = {
+	.owner = THIS_MODULE,
+	.name = "i2c-dev",
+	.dev_attrs = i2c_dev_attributes,
+};
 
 static int i2cdev_attach_adapter(struct device *dev, void *dummy)
 {
@@ -555,22 +563,17 @@  static int i2cdev_attach_adapter(struct device *dev, void *dummy)
 		return PTR_ERR(i2c_dev);
 
 	/* register this i2c device with the driver core */
-	i2c_dev->dev = device_create(i2c_dev_class, &adap->dev,
+	i2c_dev->dev = device_create(&i2c_dev_class, &adap->dev,
 				     MKDEV(I2C_MAJOR, adap->nr), NULL,
 				     "i2c-%d", adap->nr);
 	if (IS_ERR(i2c_dev->dev)) {
 		res = PTR_ERR(i2c_dev->dev);
 		goto error;
 	}
-	res = device_create_file(i2c_dev->dev, &dev_attr_name);
-	if (res)
-		goto error_destroy;
 
 	pr_debug("i2c-dev: adapter [%s] registered as minor %d\n",
 		 adap->name, adap->nr);
 	return 0;
-error_destroy:
-	device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
 error:
 	return_i2c_dev(i2c_dev);
 	return res;
@@ -589,9 +592,8 @@  static int i2cdev_detach_adapter(struct device *dev, void *dummy)
 	if (!i2c_dev) /* attach_adapter must have failed */
 		return 0;
 
-	device_remove_file(i2c_dev->dev, &dev_attr_name);
 	return_i2c_dev(i2c_dev);
-	device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
+	device_destroy(&i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
 
 	pr_debug("i2c-dev: adapter [%s] unregistered\n", adap->name);
 	return 0;
@@ -632,11 +634,9 @@  static int __init i2c_dev_init(void)
 	if (res)
 		goto out;
 
-	i2c_dev_class = class_create(THIS_MODULE, "i2c-dev");
-	if (IS_ERR(i2c_dev_class)) {
-		res = PTR_ERR(i2c_dev_class);
+	res = class_register(&i2c_dev_class);
+	if (res)
 		goto out_unreg_chrdev;
-	}
 
 	/* Keep track of adapters which will be added or removed later */
 	res = bus_register_notifier(&i2c_bus_type, &i2cdev_notifier);
@@ -649,7 +649,7 @@  static int __init i2c_dev_init(void)
 	return 0;
 
 out_unreg_class:
-	class_destroy(i2c_dev_class);
+	class_unregister(&i2c_dev_class);
 out_unreg_chrdev:
 	unregister_chrdev(I2C_MAJOR, "i2c");
 out:
@@ -661,7 +661,7 @@  static void __exit i2c_dev_exit(void)
 {
 	bus_unregister_notifier(&i2c_bus_type, &i2cdev_notifier);
 	i2c_for_each_dev(NULL, i2cdev_detach_adapter);
-	class_destroy(i2c_dev_class);
+	class_unregister(&i2c_dev_class);
 	unregister_chrdev(I2C_MAJOR, "i2c");
 }