make device inode
root@jcjung:/work/sample_driver# mknod /dev/sample c 250 0
root@jcjung:/work/sample_driver# gcc -o sample_app sample_app.c
root@jcjung:/work/sample_driver# ./sample_app
fd : 3
read ret : 0x11
write ret : 0x22
ioctl ret : 0x33
mmap ret : 0xb776b000
kernel message
root@jcjung:/work/sample_driver# dmesg | tail -10
[26803.164412] --> major : 250, minor : 0
[26803.164622] Sample Driver: read
[26803.164634] -->buf: 0x99, cnt: 0x98
[26803.164698] Sample Driver: write
[26803.164709] -->buf: 0x88, cnt: 0x87
[26803.164750] Sample driver: ioctl
[26803.164761] --> cmd: 0x77, arg: 0x76
[26803.164806] Sample driver: mmap
[26803.164817] --> start: 0xb776b000, end: 0xb7773000
[26803.165373] Sample driver: release