Linux USB Device Driver Part6 - Storing Private Data

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As there are chances to retrieve information related to interface later in the driver, usb provides an API to store pointer to any data type and saves it in usb_interface structure.

static inline void usb_set_intfdata(struct usb_interface *intf, void *data);

To retrieve the data back, we will use the following API.

static inline void *usb_get_intfdata(struct usb_interface *intf);

Let's update over previous driver code, storing a new variable int count in our private data, which represents the number of times the device has been opened

Code:

Output:


Notes:

1. In the probe function, we allocated memory for private data structure, and initialize the members, and call usb_set_intfdata to save the pointer into usb_interface data structure
2. In the open function, we first get the interface structure by using usb_find_interface API and then get the private data structure using usb_get_intfdata API
3. Finally in the disconnect function, we free the memory and set the interface data to NULL

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