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Advanced UNIX progamming

Advanced UNIX progamming. Fall 2002 Instructor: Ashok Srinivasan Lecture 8. Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan. Announcements. Reading assignment APUE Chapter 7 Section 7.3 is important

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Advanced UNIX progamming

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  1. Advanced UNIX progamming Fall 2002 Instructor: Ashok Srinivasan Lecture 8 Acknowledgements: The syllabus and power point presentations are modified versions of those by T. Baker and X. Yuan

  2. Announcements • Reading assignment • APUE Chapter 7 • Section 7.3 is important • You should know the material from 7.1, 7.2, 7.4 – 7.9 from previous courses and classes • APUE Chapter 8 • Sections 8.1-8.3, 8.5-8.6, 8.9-8.10 • You should also understand the idea behind race conditions • APUE Chapter 14 • Section 14.2

  3. Week 3 Topics • UNIX file system • File system abstraction • Directories • File descriptors • Unix API Programming Examples and Techniques • Example with direct IO • open, close, fdopen, lseek, unlink • Variable argument list

  4. Week 3 Topics ... continued • File I/O • File descriptors • open, creat, close, dup, dup2 • I/O redirection • Process management • fork, exit, wait, waitpid, execv • Pipes • Named and unnamed pipes • Implementing pipe in a shell

  5. File I/O • File descriptors • open, creat, close, dup, dup2 • I/O redirection

  6. File descriptors • Implication of the file descriptor/open file descriptions/inode table organization in UNIX • open and creat • search for the first empty slot in the process file descriptor table • allocate an open file description in the file table, which has a pointer to the inode table • See example1.c • dup and dup2 • Duplicate the file descriptor in the process file descriptor table • See example1b.c • Where is the current file position stored?

  7. I/O redirection • All UNIX processes have three predefined files open • stdin -- STDIN_FILENO (0) • stdout -- STDOUT_FILENO (1) • stderr -- STDERR_FILENO (2) • We can redirect the I/O by manipulating these file descriptors • See example2.c and example3.c

  8. Process management • fork • exit • wait and waitpid • execv

  9. fork() • fork() • Create a new process by duplicating the context of the calling process • The calling process is called the parent, and the new process the child • The return value of fork() distinguishes the two processes • See example4.c and example5.c

  10. exit() and wait() • exit (int status) • Clean up the process (for example, close all files) • Tell its parent that it is dying (SIGCHLD) • Tell child processes that it is dying (SIGHUP) • status can be accessed by the parent • wait, waitpid • Wait for a child process to die • pid_t wait(int *stat_loc) • Suspend the calling process to wait for a child process to die • Return the pid and status of the child process • See example6.c

  11. execv() • exec family system calls • Execute a command • Wipes out most of the context • The file descriptor table is kept • We can manipulate the I/O of the command by manipulating the file descriptor table • Anything after this system call will not be executed if the system call is successful • Example • int execv(const char *path, char *argv[]) • See example7.c

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