vault backup: 2022-09-22 12:37:27

content/notes/16-device-drivers.md

@@ -4,6 +4,9 @@ aliases:
 tags: 
 - lecture
 - cosc204
+sr-due: 2022-09-25
+sr-interval: 3
+sr-ease: 250
 ---
 
 # Device controller and driver
@@ -36,12 +39,65 @@ the sequence of read/write requests can (should) be optimized
 also support buffering (accepting keyboard input line by line) and editing of buffers (e.g., spcial treatement of backspace character)
 
 # IO models
-
 IO system calls use different IO models
-- blocking - when a proccess needs IO input it waits to recieve it before c
+- blocking - when a proccess needs IO input it waits to recieve it before continuing
-- non blocking
+- non blocking - waits a fixed (small) amount of time, and returns (possibly with some data still untransferred)
-- async
+- async - does not wait, is informed with a signal when io is completed
 
 # IO scheduling and buffering
+for when there are several requests for IO waiting to be serviced
+- first come firs served is not efficient
+
+IO buffers are used in main memroy to optimise file systems
+
+when a data block is used often, it is kept is memory and only written to secondary storage once all its accesses are finished
+
+# example ramdisk driver
+![](https://i.imgur.com/NIqCAzy.png)
+
+## open
+``` c
+int temp_open (struct inode *inode, struct file *filp){ 
+	// check if the process has the permission to access; 
+	// suspend the calling process if the device is busy 
+	// or used by another process; 
+	// otherwise record the id of the calling process 
+	// so that the device is owned by the process; 
+	// initialise or reset the device. 
+}
+```
+
+## read
+```c
+ssize_t temp_read(struct file *filp, char __user *buf,size_t count,loff_t *f_pos){ 
+	// find the location of data; 
+	// ask the controller to copy data to kernel kbuf 
+	// copy data to user space kbuf -> buf 
+	copy_to_user (buf, kbuf, count); 
+	*f_pos += count; // update pointer 
+	return count; // return the number of bytes read 
+}
+```
+
+## write
+```c
+ssize_t temp_write(struct file *filp, char __user *bufsize_t count, loff_t *f_pos){ 
+	// copy data from user space buf -> kbuf 
+	copy_from_user (kbuf, buf, count); 
+	// find the location of data; 
+	// ask the controller to copy data from kernel kbuf 
+	*f_pos += count; // update pointer 
+	return count; // return the number of bytes written 
+}
+```
+
+## close
+```c
+int temp_release (struct inode *inode, struct file *filp){
+	// release the device by removing the id of the process;
+	// check if there is any waiting process to wake up;
+	// undo anything done at open(), e.g. free memory. 
+}
+```
 
 # UI for IO devices

content/notes/cosc-204.md

@@ -45,6 +45,7 @@ tags:
 - [14-processes-and-system-calls](notes/14-processes-and-system-calls.md)
 - [15-file-systems](notes/15-file-systems.md)
 - [16-device-drivers](notes/16-device-drivers.md)
+
 # Archive
 
 # Info