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SubjectRe: [RFC PATCH 03/12] iio: buffer: rework buffer & scan_elements dir creation
On Tue, 17 Nov 2020 18:23:31 +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>

Hmm. This ended up a bit nasty. It could do with a few more comments
in the code to make it clear what is going on.

> ---
> drivers/iio/industrialio-buffer.c | 151 ++++++++++++++++++++++++++----
> drivers/iio/industrialio-core.c | 24 ++---
> include/linux/iio/buffer_impl.h | 14 ++-
> include/linux/iio/iio.h | 2 +-
> 4 files changed, 156 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 08aa8e0782ce..8b31faf049a5 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 +1250,101 @@ 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,
> +};
> +
> +/*
> + * This 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'

Ouch. This definitely doesn't feel like a great thing to do.

> + */
> +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]);
> +}
> +
> static int __iio_buffer_alloc_sysfs_and_mask(struct iio_buffer *buffer,

Definitely add some docs to this to say why we have this complexity..

> struct iio_dev *indio_dev)
> {
> @@ -1282,12 +1375,16 @@ 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;
>
> - 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);
> @@ -1317,28 +1414,42 @@ 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;
> }
> @@ -1366,10 +1477,14 @@ int iio_buffer_alloc_sysfs_and_mask(struct iio_dev *indio_dev)
>
> 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);
> }
>
> void iio_buffer_free_sysfs_and_mask(struct iio_dev *indio_dev)
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index ca8b11541477..f389d8feacb0 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1819,18 +1819,11 @@ 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) {
> @@ -1859,14 +1852,21 @@ 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);

There are some races around late creation of sysfs files (IIRC) but
I'm not sure what else could be done here.
Looking at device_add it is probably to do with the various notifiers being
called before we have put everything in place.

> + 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;
> @@ -1882,6 +1882,8 @@ 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);
> @@ -1899,8 +1901,6 @@ 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 9a3cf4815148..2ea185340a3a 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;
>

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