Sytem Call on File System

1. Sytem Call on File System Open Close Read/Write

2. File System용 시스템호출 • 기존의 파일을 접근하는 시스템호출 • open, read, write, close • 새로운 파일을 생성하는 시스템호출 • create, mknod • Inode를 조작하거나 파일 시스템 내부 참조용 시스템호출 • chdir, chroot, chown, chmod, stat, fstat • 기타 • pipe, dup • mount, umount • link, unlink SunMoon University

3. File Descriptor Table • U_block 내의 open file table • 내용 : • user program이 파일을 open하는 순서에 따라 파일에 integer를 assign • called “File Descriptor” • 0,1,2, assigned for terminal(standard input/output/diagonistic) • FD returned by open, create system calls • Pointer to system file table SunMoon University

4. System File Table(=File Table) • Frequently changed • Some process may share file offset • Ex.) % ls -al | grep ‘^d’ • Share same file(pipe) • But different offset • One entry for each open/create/pipe file SunMoon University

5. Contents of S.F.T. • R/W/P(pipe) flag • Offset (next byte to R or W) • Counter(# of processes using this offset) • Pointer to inode table SunMoon University

6. Mount Table • Device nimber(major and minor) • Pointer to buffer containing file system superblock • Pointer to in-core inode of directory where file system is being mounted • Pointer to in-core inode of root directory of new file system • Mount flags SunMoon University

7. Open() • fd = open( pathname, flags, modes ) • 프로세스가 아래의 코드를 수행 • fd1 = open(“/etc/passwd”, O_RDONLY); • fd1 = open(“private”, O_RDONLY); • 각각의 open call이 user file descriptor table 및 kernel file table에 하나의 항을 설정함. • File Table 을 별도로 독립시킨 이유 : • 여러 사용자들이 offset pointer를 공유할 수 있게 함.(dup 및 fork가 사용) SunMoon University

8. Algorithm of Open() • Fig 5-2 • namei  file name 을 inode로 변환 • check file permission • find in-core inode • allocate an file table entry  pointer to inode + byte /offset • allocate user filr tab;le entry • return( user file descriptor ) SunMoon University

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