Linux Device Drivers Development

Per-device data

For each open performed on your character device, the callback function will be given a struct inode as a parameter, which is the kernel lower-level representation of the file. That struct inode structure has a field named i_cdev, which points to the cdev we have allocated in the init function. By embedding the struct cdev in our device-specific data, as in struct pcf2127 in the following example, we will be able to get a pointer on that specific data using the container_of macro. Here is an open method sample.

The following is our data structure:

struct pcf2127 { 
    struct cdev cdev; 
    unsigned char *sram_data; 
    struct i2c_client *client; 
    int sram_size; 
    [...] 
}; 

Given this data structure, the open method would look like this: ...