week 10 linux device drivers

Question 1

what is a device driver

Answer 1

View from user space:
Have special file in /dev associated with it, together with five
systems calls:
open: make device available
read: read from device
write: write to device
ioctl: Perform operations on device (optional)
close: make device unavailable

Question 2

what are the five systems calls in a device driver.

Answer 2

open
read
write
ioctl
close

Question 3

what is the open system call

Answer 3

make device available

Question 4

what is the read system call

Answer 4

read from device

Question 5

what is the write system call

Answer 5

write to device

Question 6

what is the ioctl system call

Answer 6

Perform operations on device (optional)

Question 7

what is the close system call

Answer 7

makes device unavailable

Question 8

for device drivers there is one optional system call, what is it?

Answer 8

ioctl -> Perform operations on device (optional)

Question 9

how can you list the the available options of a file in linux on the kernel side

Answer 9

linux/fs.h lists all available operations on files
Each file may have functions associated with it which are called
when corresponding system calls are made

Question 10

what does kernel also keep track of

Answer 10

Physical dependencies between devices ,Example:
devices connected to a USB-hub
Buses: Channels between processor and one or more devices.
Can be either physical (eg pci, usb), or logical
Classes: Sets of devices of the same type, eg keyboards, mice

Question 11

what is physical dependencies between devices in a kernel

Answer 11

. Example:
devices connected to a USB-hub

Question 12

what are buses in a kernel

Answer 12

Channels between processor and one or more devices.

Question 13

what are classes in a kernel

Answer 13

Classes: Sets of devices of the same type, eg keyboards, mice

Question 14

what are the the types of buses in a a kernel

Answer 14

Can be either physical (eg pci, usb), or logical

Question 15

how to handle interrupts in a device driver

Answer 15

Normal cycle of interrupt handling for devices: Device sends interrupt
CPU selects appropriate interrupt handler
Interrupt handler processes interrupt
Two important tasks to be done:
Data to be transferred to/from device
Waking up processes which wait for data transfer to be finished Interrupt handler clears interrupt bit of device
Necessary for next interrupt to arrive

Question 16

describe the 2 halves of interrupt processing:

Answer 16

Interrupt processing time must be as short as possible
Data transfer fast, rest of processing slow
⇒ Separate interrupt processing in two halves:
Top Half is called directly by interrupt handler
Only transfers data between device and appropriate kernel
buffer and schedules software interrupt to start Bottom half
Bottom half still runs in interrupt context and does the rest of
the processing (eg working through the protocol stack, and
waking up processes)

Question 17

describe top half in interrupt processing

Answer 17

Top Half is called directly by interrupt handler
Only transfers data between device and appropriate kernel
buffer and schedules software interrupt to start Bottom half

Question 18

describe bottom half in interrupt processing

Answer 18

Bottom half still runs in interrupt context and does the rest of
the processing (eg working through the protocol stack, and
waking up processes)