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Date:   Sun, 24 Jan 2021 18:11:26 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     Alexandru Ardelean <alexandru.ardelean@analog.com>
Cc:     <linux-kernel@vger.kernel.org>, <linux-iio@vger.kernel.org>,
        <lars@metafoo.de>, <Michael.Hennerich@analog.com>,
        <nuno.sa@analog.com>, <dragos.bogdan@analog.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Subject: Re: [PATCH v2 03/12][RESEND] iio: buffer: rework buffer &
 scan_elements dir creation
Message-ID: <20210124181126.07c100a5@archlinux>
In-Reply-To: <20210122162529.84978-4-alexandru.ardelean@analog.com>
References: <20210122162529.84978-1-alexandru.ardelean@analog.com>
        <20210122162529.84978-4-alexandru.ardelean@analog.com>
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On Fri, 22 Jan 2021 18:25:20 +0200
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> When adding more than one IIO buffer per IIO device, we will need to create
> a buffer & scan_elements directory for each buffer.
> We also want to move the 'scan_elements' to be a sub-directory of the
> 'buffer' folder.
> 
> The format we want to reach is, for a iio:device0 folder, for 2 buffers
> [for example], we have a 'buffer0' and a 'buffer1' subfolder, and each with
> it's own 'scan_elements' subfolder.
> 
> So, for example:
>    iio:device0/buffer0
>       scan_elements/
> 
>    iio:device0/buffer1
>       scan_elements/
> 
> The other attributes under 'bufferX' would remain unchanged.
> 
> However, we would also need to symlink back to the old 'buffer' &
> 'scan_elements' folders, to keep backwards compatibility.
> 
> Doing all these, require that we maintain the kobjects for each 'bufferX'
> and 'scan_elements' so that we can symlink them back. We also need to
> implement the sysfs_ops for these folders.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>

+CC GregKH and Rafael W for feedback on various things inline.

It might be that this is the neatest solution that we can come up with but
more eyes would be good!

Whilst I think this looks fine, I'm less confident than I'd like to be.

Jonathan

> ---
>  drivers/iio/industrialio-buffer.c | 195 +++++++++++++++++++++++++++---
>  drivers/iio/industrialio-core.c   |  24 ++--
>  include/linux/iio/buffer_impl.h   |  14 ++-
>  include/linux/iio/iio.h           |   2 +-
>  4 files changed, 200 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 0412c4fda4c1..0f470d902790 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c
> @@ -1175,8 +1175,6 @@ static ssize_t iio_buffer_store_enable(struct device *dev,
>  	return (ret < 0) ? ret : len;
>  }
>  
> -static const char * const iio_scan_elements_group_name = "scan_elements";
> -
>  static ssize_t iio_buffer_show_watermark(struct device *dev,
>  					 struct device_attribute *attr,
>  					 char *buf)
> @@ -1252,6 +1250,124 @@ static struct attribute *iio_buffer_attrs[] = {
>  	&dev_attr_data_available.attr,
>  };
>  
> +#define to_dev_attr(_attr) container_of(_attr, struct device_attribute, attr)
> +
> +static ssize_t iio_buffer_dir_attr_show(struct kobject *kobj,
> +					struct attribute *attr,
> +					char *buf)
> +{
> +	struct iio_buffer *buffer = container_of(kobj, struct iio_buffer, buffer_dir);
> +	struct device_attribute *dattr;
> +
> +	dattr = to_dev_attr(attr);
> +
> +	return dattr->show(&buffer->indio_dev->dev, dattr, buf);
> +}
> +
> +static ssize_t iio_buffer_dir_attr_store(struct kobject *kobj,
> +					 struct attribute *attr,
> +					 const char *buf,
> +					 size_t len)
> +{
> +	struct iio_buffer *buffer = container_of(kobj, struct iio_buffer, buffer_dir);
> +	struct device_attribute *dattr;
> +
> +	dattr = to_dev_attr(attr);
> +
> +	return dattr->store(&buffer->indio_dev->dev, dattr, buf, len);
> +}
> +
> +static const struct sysfs_ops iio_buffer_dir_sysfs_ops = {
> +	.show = iio_buffer_dir_attr_show,
> +	.store = iio_buffer_dir_attr_store,
> +};
> +
> +static struct kobj_type iio_buffer_dir_ktype = {
> +	.sysfs_ops = &iio_buffer_dir_sysfs_ops,
> +};
> +
> +static ssize_t iio_scan_el_dir_attr_show(struct kobject *kobj,
> +					 struct attribute *attr,
> +					 char *buf)
> +{
> +	struct iio_buffer *buffer = container_of(kobj, struct iio_buffer, scan_el_dir);
> +	struct device_attribute *dattr = to_dev_attr(attr);
> +
> +	return dattr->show(&buffer->indio_dev->dev, dattr, buf);
> +}
> +
> +static ssize_t iio_scan_el_dir_attr_store(struct kobject *kobj,
> +					  struct attribute *attr,
> +					  const char *buf,
> +					  size_t len)
> +{
> +	struct iio_buffer *buffer = container_of(kobj, struct iio_buffer, scan_el_dir);
> +	struct device_attribute *dattr = to_dev_attr(attr);
> +
> +	return dattr->store(&buffer->indio_dev->dev, dattr, buf, len);
> +}
> +
> +static const struct sysfs_ops iio_scan_el_dir_sysfs_ops = {
> +	.show = iio_scan_el_dir_attr_show,
> +	.store = iio_scan_el_dir_attr_store,
> +};
> +
> +static struct kobj_type iio_scan_el_dir_ktype = {
> +	.sysfs_ops = &iio_scan_el_dir_sysfs_ops,
> +};
> +
> +/*
> + * These iio_sysfs_{add,del}_attrs() are essentially re-implementations of
> + * sysfs_create_files() & sysfs_remove_files(), but they are meant to get
> + * around the const-pointer mismatch situation with using them.
> + *
> + * sysfs_{create,remove}_files() uses 'const struct attribute * const *ptr',
> + * while these are happy with just 'struct attribute **ptr'
> + */

Then to my mind the question becomes why sysfs_create_files() etc requires
the second level of const.  If there is justification for that relaxation here
we should make it more generally.

> +static int iio_sysfs_add_attrs(struct kobject *kobj, struct attribute **ptr)
> +{
> +	int err = 0;
> +	int i;
> +
> +	for (i = 0; ptr[i] && !err; i++)
> +		err = sysfs_create_file(kobj, ptr[i]);
> +	if (err)
> +		while (--i >= 0)
> +			sysfs_remove_file(kobj, ptr[i]);
> +	return err;
> +}
> +
> +static void iio_sysfs_del_attrs(struct kobject *kobj, struct attribute **ptr)
> +{
> +	int i;
> +
> +	for (i = 0; ptr[i]; i++)
> +		sysfs_remove_file(kobj, ptr[i]);
> +}
> +
> +/**
> + * __iio_buffer_alloc_sysfs_and_mask() - Allocate sysfs attributes to an attached buffer
> + * @buffer: the buffer object for which the sysfs attributes are created for
> + * @indio_dev: the iio device to which the iio buffer belongs to
> + *
> + * Return 0, or negative for error.
> + *
> + * This function must be called for each single buffer. The sysfs attributes for that
> + * buffer will be created, and the IIO device object will be the parent kobject of that
> + * the kobjects created here.
> + * Because we need to redirect sysfs attribute to it's IIO buffer object, we need to
> + * implement our own sysfs_ops, and each IIO buffer will keep a kobject for the
> + * 'bufferX' directory and one for the 'scan_elements' directory.
> + * And in order to do this, this function must be called after the IIO device object
> + * has been added via device_add(). This fundamentally changes how sysfs attributes
> + * were created before (with one single IIO buffer per IIO device), where the
> + * sysfs attributes for the buffer were mapped as attribute groups on the IIO device
> + * groups object list.

Been a while, so I can't recall the exact reasons this can cause problems.
I've +CC Greg and Rafael for comments.

For their reference, the aim of this set is undo an old restriction on IIO that devices
only had one buffer.  To do that we need to keep a iio:deviceX/buffer0 directory
also exposed as iio:deviceX/buffer/* and
iio:deviceX/buffer0/scan_elements/ as iio:deviceX/scan_elements.
to maintain backwards compatibility.


> + * Using kobjects directly for the 'bufferX' and 'scan_elements' directories allows
> + * us to symlink them back to keep backwards compatibility for the old sysfs interface
> + * for IIO buffers while also allowing us to support multiple IIO buffers per one
> + * IIO device.
> + */
>  static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
>  					     struct iio_dev *indio_dev)
>  {
> @@ -1282,12 +1398,16 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
>  		memcpy(&attr[ARRAY_SIZE(iio_buffer_attrs)], buffer->attrs,
>  		       sizeof(struct attribute *) * attrcount);
>  
> -	attr[attrcount + ARRAY_SIZE(iio_buffer_attrs)] = NULL;
> +	buffer->buffer_attrs = attr;
>  
> -	buffer->buffer_group.name = "buffer";
> -	buffer->buffer_group.attrs = attr;
> +	ret = kobject_init_and_add(&buffer->buffer_dir, &iio_buffer_dir_ktype,
> +				   &indio_dev->dev.kobj, "buffer");
> +	if (ret)
> +		goto error_buffer_free_attrs;
>  

Do we potentially want kobject_uevent calls for these?
(based on looking at similar code in edac).

> -	indio_dev->groups[indio_dev->groupcounter++] = &buffer->buffer_group;
> +	ret = iio_sysfs_add_attrs(&buffer->buffer_dir, buffer->buffer_attrs);
> +	if (ret)
> +		goto error_buffer_kobject_put;
>  
>  	attrcount = 0;
>  	INIT_LIST_HEAD(&buffer->scan_el_dev_attr_list);
> @@ -1317,32 +1437,57 @@ static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,
>  		}
>  	}
>  
> -	buffer->scan_el_group.name = iio_scan_elements_group_name;
> -
> -	buffer->scan_el_group.attrs = kcalloc(attrcount + 1,
> -					      sizeof(buffer->scan_el_group.attrs[0]),
> -					      GFP_KERNEL);
> -	if (buffer->scan_el_group.attrs == NULL) {
> +	buffer->scan_el_attrs = kcalloc(attrcount + 1,
> +					sizeof(buffer->scan_el_attrs[0]),
> +					GFP_KERNEL);
> +	if (buffer->scan_el_attrs == NULL) {
>  		ret = -ENOMEM;
>  		goto error_free_scan_mask;
>  	}
> -	attrn = 0;
>  
> +	ret = kobject_init_and_add(&buffer->scan_el_dir, &iio_scan_el_dir_ktype,
> +				   &indio_dev->dev.kobj, "scan_elements");
> +	if (ret)
> +		goto error_free_scan_attrs;
> +
> +	attrn = 0;
>  	list_for_each_entry(p, &buffer->scan_el_dev_attr_list, l)
> -		buffer->scan_el_group.attrs[attrn++] = &p->dev_attr.attr;
> -	indio_dev->groups[indio_dev->groupcounter++] = &buffer->scan_el_group;
> +		buffer->scan_el_attrs[attrn++] = &p->dev_attr.attr;
> +
> +	ret = iio_sysfs_add_attrs(&buffer->scan_el_dir, buffer->scan_el_attrs);
> +	if (ret)
> +		goto error_scan_kobject_put;
>  
>  	return 0;
>  
> +error_scan_kobject_put:
> +	kobject_put(&buffer->scan_el_dir);
> +error_free_scan_attrs:
> +	kfree(buffer->scan_el_attrs);
>  error_free_scan_mask:
>  	bitmap_free(buffer->scan_mask);
>  error_cleanup_dynamic:
> +	iio_sysfs_del_attrs(&buffer->buffer_dir, buffer->buffer_attrs);
>  	iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
> -	kfree(buffer->buffer_group.attrs);
> +error_buffer_kobject_put:
> +	kobject_put(&buffer->buffer_dir);
> +error_buffer_free_attrs:
> +	kfree(buffer->buffer_attrs);
>  
>  	return ret;
>  }
>  
> +/**
> + * iio_buffer_alloc_sysfs_and_mask() - Allocate sysfs attributes to attached buffers
> + * @indio_dev: the iio device for which to create the buffer sysfs attributes
> + *
> + * Return 0, or negative for error.
> + *
> + * If the IIO device has no buffer attached, no sysfs attributes will be created.
> + * This function must be called after the IIO device object has been created and
> + * registered with device_add(). See __iio_buffer_alloc_sysfs_and_mask() for more
> + * details.
> + */
>  int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
>  {
>  	struct iio_buffer *buffer = indio_dev->buffer;
> @@ -1364,14 +1509,28 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
>  	return __iio_buffer_alloc_sysfs_and_mask(buffer, indio_dev);
>  }
>  
> +/**
> + * __iio_buffer_free_sysfs_and_mask() - Free sysfs objects for a single IIO buffer
> + * @buffer: the iio buffer for which to destroy the objects
> + */
>  static void __iio_buffer_free_sysfs_and_mask(struct iio_buffer *buffer)
>  {
> +	iio_sysfs_del_attrs(&buffer->scan_el_dir, buffer->scan_el_attrs);
> +	kobject_put(&buffer->scan_el_dir);
> +	kfree(buffer->scan_el_attrs);
>  	bitmap_free(buffer->scan_mask);
> -	kfree(buffer->buffer_group.attrs);
> -	kfree(buffer->scan_el_group.attrs);
> +	iio_sysfs_del_attrs(&buffer->buffer_dir, buffer->buffer_attrs);
>  	iio_free_chan_devattr_list(&buffer->scan_el_dev_attr_list);
> +	kobject_put(&buffer->buffer_dir);
> +	kfree(buffer->buffer_attrs);
>  }
>  
> +/**
> + * iio_buffer_free_sysfs_and_mask() - Free sysfs objects for all IIO buffers
> + * @indio_dev: the iio device for which to destroy the objects
> + *
> + * If the IIO device has no buffer attached, nothing will be done.
> + */
>  void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
>  {
>  	struct iio_buffer *buffer = indio_dev->buffer;
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 0a6fd299a978..95d66745f118 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1817,18 +1817,11 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
>  
>  	iio_device_register_debugfs(indio_dev);
>  
> -	ret = iio_buffer_alloc_sysfs_and_mask(indio_dev);
> -	if (ret) {
> -		dev_err(indio_dev->dev.parent,
> -			"Failed to create buffer sysfs interfaces\n");
> -		goto error_unreg_debugfs;
> -	}
> -
>  	ret = iio_device_register_sysfs(indio_dev);
>  	if (ret) {
>  		dev_err(indio_dev->dev.parent,
>  			"Failed to register sysfs interfaces\n");
> -		goto error_buffer_free_sysfs;
> +		goto error_unreg_debugfs;
>  	}
>  	ret = iio_device_register_eventset(indio_dev);
>  	if (ret) {
> @@ -1857,14 +1850,21 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
>  	if (ret < 0)
>  		goto error_unreg_eventset;
>  
> +	ret = iio_buffer_alloc_sysfs_and_mask(indio_dev);
> +	if (ret) {
> +		dev_err(indio_dev->dev.parent,
> +			"Failed to create buffer sysfs interfaces\n");
> +		goto error_device_del;
> +	}
> +
>  	return 0;
>  
> +error_device_del:
> +	cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
>  error_unreg_eventset:
>  	iio_device_unregister_eventset(indio_dev);
>  error_free_sysfs:
>  	iio_device_unregister_sysfs(indio_dev);
> -error_buffer_free_sysfs:
> -	iio_buffer_free_sysfs_and_mask(indio_dev);
>  error_unreg_debugfs:
>  	iio_device_unregister_debugfs(indio_dev);
>  	return ret;
> @@ -1880,6 +1880,8 @@ void iio_device_unregister(struct iio_dev *indio_dev)
>  	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
>  	struct iio_ioctl_handler *h, *t;
>  
> +	iio_buffer_free_sysfs_and_mask(indio_dev);
> +
>  	cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
>  
>  	mutex_lock(&indio_dev->info_exist_lock);
> @@ -1897,8 +1899,6 @@ void iio_device_unregister(struct iio_dev *indio_dev)
>  	iio_buffer_wakeup_poll(indio_dev);
>  
>  	mutex_unlock(&indio_dev->info_exist_lock);
> -
> -	iio_buffer_free_sysfs_and_mask(indio_dev);
>  }
>  EXPORT_SYMBOL(iio_device_unregister);
>  
> diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> index 67d73d465e02..77e169e51434 100644
> --- a/include/linux/iio/buffer_impl.h
> +++ b/include/linux/iio/buffer_impl.h
> @@ -103,14 +103,20 @@ struct iio_buffer {
>  	/* @scan_el_dev_attr_list: List of scan element related attributes. */
>  	struct list_head scan_el_dev_attr_list;
>  
> -	/* @buffer_group: Attributes of the buffer group. */
> -	struct attribute_group buffer_group;
> +	/* @buffer_dir: kobject for the 'buffer' directory of this buffer */
> +	struct kobject buffer_dir;
> +
> +	/* @buffer_attrs: Attributes of the buffer group. */
> +	struct attribute **buffer_attrs;
> +
> +	/* @scan_el_dir: kobject for the 'scan_elements' directory of this buffer */
> +	struct kobject scan_el_dir;
>  
>  	/*
> -	 * @scan_el_group: Attribute group for those attributes not
> +	 * @scan_el_attrs: Array of attributes for those attributes not
>  	 * created from the iio_chan_info array.
>  	 */
> -	struct attribute_group scan_el_group;
> +	struct attribute **scan_el_attrs;
>  
>  	/* @attrs: Standard attributes of the buffer. */
>  	const struct attribute **attrs;
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index e4a9822e6495..59b317dc45b8 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -556,7 +556,7 @@ struct iio_dev {
>  	struct mutex			info_exist_lock;
>  	const struct iio_buffer_setup_ops	*setup_ops;
>  	struct cdev			chrdev;
> -#define IIO_MAX_GROUPS 6
> +#define IIO_MAX_GROUPS 4
>  	const struct attribute_group	*groups[IIO_MAX_GROUPS + 1];
>  	int				groupcounter;
>