driver

• driver custom struct
  • module_init, module_exit
  • store cdev
• inode
  • only one inode for each file, but multiple filp can exist
  • dev_t?
  • cdev * how about other type?
• filp: file descriptor
  • void *private_data
    • usually set to the driver’s custom struct
  • struct file_operations *f_op
    • store pointer syscall implementation

present status

• generate /proc file: not recommanded because proc should only be about process
  • seq_file:
• ioctl: transmit data to user space when asked
• sysfs:

ioctl

• command number
• command struct

char device

• sequential access
• cdev_init

block device

• random, page access

access control

• uid, gid
• capability
• cgroup?
  • limit resource usage

namespace

Changes to the global resource are visible to other processes that are members of the namespace, but are invisible to other processes

• mnt, pid, net, ipc, UTS, user, cgroup, time
• lsns: show process namespace
• unshare: move the calling process to another ns

time

• timer interrupt
  • jiffies, jiffies_64, HZ
• cpu cycle register
  • x86: TSC
• timespec
  • second + nanosecond
• timeval
  • second + microsecond

wait queue

exclusive

atomic

• semaphore
  • mutex
• spinlock

• atomic

• in_interrupt()
  • in hardware or software interrupt
• in_atomic
  • interrput + if spinlock is held

delay

• busy wait
  • cpu_relax()
• yield
  • schedule()
  • no guarantee of reschedule
• timeout
  • wait_event_timeout
  • schedule_timeout
    • set_current_state
• delay
  • mdelay
  • msleep

future work

• timer: linux/timer.h
  • add_timer
    • timer only get schduled on the same CPU?
    • timer function can reschedule itself
  • del_timer
    • ensure that timer is not queued
    • return non-zero if the timer is actually dequeued
      • timer might already finished
    • delete might be done on another CPU
  • del_timer_sync
    • also ensure that timer is not executing at return
    • this function can sleep
    • ensure function does not reschedule itself
• tasklet: schedule function to be called later
  • no time specified, but no later than next time tick
• workqueue: in kernel process context
  • per-cpu thread might be inited
  • queue_work
  • shared workqueue: schedule_work()

interrupt

memory

• memory mapping
  • /proc/iomem
    • embedded in normal memory range
    • non-prefetchable
  • /proc/ioports
    • special instruction required
  • nopage / remap_pfn_range
• dma
  • bus address

sys, proc, dev

sysfs

• /sys contains the running information for the system
  • each driver will create one directory in the tree
    • module relationship is expressed as symbolic link
  • each attribute becomes one file in the directory
• different folder represents the structure in different ways
  • /sys/devices: describe devices’ physical connection
  • /sys/dev: char and block device
  • /sys/class: based on devices’ function
  • /sys/bus: based on interconnect type

https://www.kernel.org/doc/Documentation/filesystems/sysfs.txt https://www.kernel.org/doc/html/latest/admin-guide/sysfs-rules.html

proc

• /proc decribes running information for each process
  • cpuinfo
  • meminfo
    • slabtop
    • pmap
  • iomem, ioport
• device tree:
  • /proc/device-tree/
  • of-node

dev

• simulated file for actual data transfer
• https://www.kernel.org/doc/Documentation/admin-guide/devices.txt

reference

Linux Specfication

Interactive Linux Kernel Map