character-device-driver

Repository implements a character special device driver to read and write to a hypothetical device

You are going to write a character special device driver in the following ways:

1. Define a device structure and embed structure cdev in that structure: struct asp_mycdev { struct cdev dev; char *ramdisk; struct semaphore sem; int devNo; // any other field you may want to add };

2. Support a variable number of devices that can be set at load time (default will be 3) (see DDScullBasic.pptx). The device nodes will be named /dev/mycdev0, /dev/mycdev1, ..., /dev/mycdevN-1, where N is the number of devices. Please have the device driver create the device nodes.

3. Provide an entry function that would be accessed via lseek() function. That entry function should update the file position pointer based on the offset requested. You should set the file position pointer as requested as long as it does not go out of bounds, i.e., 0 requestedposition.

In the case of a request that goes beyond end of the buffer, your implementation needs to expand the buffer and fill the new region with zeros.

4. Provide an entry function that would be accessed via ioctl() function. You should let the user application clear the data stored in the ramdisk. You should define symbol ASP CLEAR BUF for the command to clear the buffer. Your driver function should also reset the file position pointer to 0. Please see DDScullBasic.pptx for implementation details.

5. Each device can be opened concurrently and therefore can be accessed for read, write, lseek, and ioctl concurrently. It is your responsibility to provide appropriate synchronization to prevent race conditions.

6. All the resources (including the ramdisk, the device structures, and device nodes) should be recycled/freed at the time of unloading your device driver module.

Instructions on how the module will be tested :

Copy the files char_driver.c, Makefile and userapp.c to a virtual linux machine and follow the following steps:

1. Compile driver module : $ make

2. Load module : $ sudo insmod char_driver.ko NUM_DEVICES=<num_devices> or use : sudo insmod char_driver.ko

3. Test driver :

   1. Compile userapp : $ make app
   2. Run userapp : $ sudo ./userapp <device_number> where device_number identifies the id number of the device to be tested.

   Note : userapp has to be executed with sudo privilege as the device files in /dev/ are created in the driver with root privileges.

4. Unload module : $ sudo rmmod char_driver