2023.11.16 TIL

Code, Image source: The Linux Programming Interface, Michael Kerrisk

Memory 관련 System Call

Memory Mapping

mmap() system call

• Process address space에 새로운 memory mapping 생성
  • Mapping type : File
  • Mapping type : Anonymous

Process sharing

• Process
  • File mapping으로 공유
  • fork()로 생성된 child process 참조

Private/Shared

• MAP_PRIVATE
  • Process간 공유 X
• MAP_SHARED
  • Process간 공유

File, Private

• File을 memory처럼 읽을 수 있음. Memory 할당 없이!
  

File, Shared

• IPC
  • tlpi-dist/mmap/t_mmap.c
  • $ dd if=/def/zero of=s.txt bs=1 count=1024 → file copy
  • $ ./t_mmap s.txt hello
  • $ ./t_mmap s.txt goodbye
  • $ od -c -w8 s.txt

Mapping 생성 - mmap()

#include <sys/mman.h>

void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);

• flags : Private / Shared
• Ex: addr = mmap(NULL, length, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); if(addr == MAP_FAILED) errExit("mmap");
• tlpi-dist/mmap/mmcat.c

Mapp 영역 해제 - munmap()

#include <sys/mman.h>

int munmap(void *addr, size_t length);

Memory Protection Mode Changing - mprotect()

#include <sys/mman.h>

int mprotect(void *addr, size_t length, int prot);

• tlpi-dist/vmem/t_mprotect.c

Memory lock - mlock(), mlockall()

#include <sys/mman.h>

int mlock(void *addr, size_t length);
int munlock(void *addr, size_t length);

• tlpi-dist/vmem/memlock.c

File System 관련 System Call

File I/O Buffering

• Kernel buffer cache

File System 구조

• Disk virtualization

I-node

• File format, owner, group, size, block number, block pointer

VFS(Virtual File System)

• Virtualization of open, read, write, close
• 하나의 interface로 호출

File System mount - mount()

#include <sys/mount.h>

int mount(const char *source, const char *target, const char *fstype, unsigned long mountflags, const void *data);

File attributes

Hard Link, Symbolic Link

• Symbolic Link
  • 원본 파일을 지워도 I-node에 남아있다

File event monitoring

#include <sys/inotify.h>

int inotify_init(void);  // return fd on success, -1 on error

int inotify_add_watch(int fd, const char *pathname, uint32_t mask);  // return watch descriptor on success, -1 on error

• File, directory 변화 감지
• tlpi-dist/inotify/demo_inotify.c