I am having some basic question about the usage of structure pointer in linux device drivers.
Taking an example of RTC ISL12022 driver linux/drivers/rtc/rtc-isl12022.c
struct isl12022 *isl12022 = i2c_get_clientdata(client); //From Function static int
isl12022_set_datetime(struct i2c_client *client, struct rtc_time *tm)
In above example structure pointer is used to get the I2C client data instead of creating local copyinto the function. Mostly I have seen such practice in all the drivers. Hereby I am looking to know about the pros of using structure pointer instead of creating local copy?
-----------------------------------EDIT-----------------------------------------------
Nicely Explained. Thanks. When passing the structure to the function pointer needs to be used, Agree on it. But considering the above rtc-isl12022.c example taking function
isl12022_set_datetime(struct i2c_client *client, struct rtc_time *tm)
the i2c_client structure is already passed to the function as pointer. (Thats there)
Now inside the isl12022_set_datetime function *client pointer has been used directly instead of creating local copy of it and then using that copy to ensure that by mistake original structure pointed by *client is safe and unaltered.
struct isl12022 isl2022; and then copy the structure pointed as i2c_get_clientdata(client);
The above statement will create isl12022 structure pointer which points to isl12022 structure returned by i2c_get_clientdata fn. Wont be that distrub the original datastructure which is pointed by client?
