Re: [PATCH v2 3/5] nvmem: expose nvmem cells as cdev

[Marco Felsch <m.felsch@pengutronix.de>]

On 24-06-14, Sascha Hauer wrote:
> On Thu, Jun 13, 2024 at 03:15:29PM +0200, Marco Felsch wrote:
> > Expose the nvmem cells via cdevs which is our equivalent to the Linux
> > sysfs exposure. This allows the easier user queries for board code and
> > shell. Keep the Linux function name scheme for
> > nvmem_populate_sysfs_cells() to reduce the diff for nvmem_register()
> > function.
> > 
> > Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> > ---
> > v2:
> > - fix error handling path during nvmem_register
> > - drop useless list_empty()
> > 
> >  drivers/nvmem/core.c | 101 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 101 insertions(+)
> > 
> > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> > index ee7d4c6301c3..8e91d9c0fc8a 100644
> > --- a/drivers/nvmem/core.c
> > +++ b/drivers/nvmem/core.c
> > @@ -44,6 +44,8 @@ struct nvmem_cell_entry {
> >  	struct device_node	*np;
> >  	struct nvmem_device	*nvmem;
> >  	struct list_head	node;
> > +
> > +	struct cdev		cdev;
> >  };
> >  
> >  struct nvmem_cell {
> > @@ -144,6 +146,101 @@ static struct nvmem_device *of_nvmem_find(struct device_node *nvmem_np)
> >  	return NULL;
> >  }
> >  
> > +static struct nvmem_cell *nvmem_create_cell(struct nvmem_cell_entry *entry,
> > +					    const char *id, int index);
> > +
> > +static ssize_t nvmem_cell_cdev_read(struct cdev *cdev, void *buf, size_t count,
> > +				    loff_t offset, unsigned long flags)
> > +{
> > +	struct nvmem_cell_entry *entry;
> > +	struct nvmem_cell *cell = NULL;
> > +	size_t cell_sz, read_len;
> > +	void *content;
> > +
> > +	entry = container_of(cdev, struct nvmem_cell_entry, cdev);
> > +	cell = nvmem_create_cell(entry, entry->name, 0);
> > +	if (IS_ERR(cell))
> > +		return PTR_ERR(cell);
> > +
> > +	content = nvmem_cell_read(cell, &cell_sz);
> > +	if (IS_ERR(content)) {
> > +		read_len = PTR_ERR(content);
> > +		goto destroy_cell;
> > +	}
> > +
> > +	read_len = min_t(unsigned int, cell_sz - offset, count);
> > +	memcpy(buf, content + offset, read_len);
> > +	kfree(content);
> > +
> > +destroy_cell:
> > +	kfree_const(cell->id);
> > +	kfree(cell);
> > +
> > +	return read_len;
> > +}
> > +
> > +static ssize_t nvmem_cell_cdev_write(struct cdev *cdev, const void *buf, size_t count,
> > +				     loff_t offset, unsigned long flags)
> > +{
> > +	struct nvmem_cell_entry *entry;
> > +	struct nvmem_cell *cell;
> > +	int ret;
> > +
> > +	entry = container_of(cdev, struct nvmem_cell_entry, cdev);
> > +
> > +	if (!entry->nvmem->reg_write)
> > +		return -EPERM;
> > +
> > +	if (offset >= entry->bytes)
> > +		return -EFBIG;
> > +
> > +	if (offset + count > entry->bytes)
> > +		count = entry->bytes - offset;
> > +
> > +	cell = nvmem_create_cell(entry, entry->name, 0);
> > +	if (IS_ERR(cell))
> > +		return PTR_ERR(cell);
> > +
> > +	if (!cell)
> > +		return -EINVAL;
> > +
> > +	ret = nvmem_cell_write(cell, buf, count);
> > +
> > +	kfree_const(cell->id);
> > +	kfree(cell);
> > +
> > +	return ret;
> > +}
> > +
> > +static struct cdev_operations nvmem_cell_chrdev_ops = {
> > +	.read  = nvmem_cell_cdev_read,
> > +	.write = nvmem_cell_cdev_write,
> > +};
> > +
> > +static int nvmem_populate_sysfs_cells(struct nvmem_device *nvmem)
> > +{
> > +	struct device *dev = &nvmem->dev;
> > +	struct nvmem_cell_entry *entry;
> > +
> > +	list_for_each_entry(entry, &nvmem->cells, node) {
> > +		struct cdev *cdev;
> > +		int ret;
> > +
> > +		cdev = &entry->cdev;
> > +		cdev->name = xasprintf("%s.%s", dev_name(dev),
> > +				       kbasename(entry->name));
> > +		cdev->ops = &nvmem_cell_chrdev_ops;
> > +		cdev->dev = dev;
> > +		cdev->size = entry->bytes;
> > +
> > +		ret = devfs_create(cdev);
> > +		if (ret)
> > +			return ret;
> 
> You might fail here without unregistering the already registered cells.

Argh.. you're right. I will give it a 3th spin. Thanks for the review.

Regards,
  Marco

> Furthermore you free the nvmem device which likely leads to memory
> corruptions further down. Your choices are:
> 
> - Do not fail here, but only print a warning when devfs_create() fails,
>   or:
> - properly unregister what you registered beforehand.
> 
> Sascha
> 
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