8.16 Exercises

  1. 1.
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    Why panic in balloc ? Can xv6 recover?

  2. 2.
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    Why panic in ialloc ? Can xv6 recover?

  3. 3.
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    Why doesn’t filealloc panic when it runs out of files? Why is this more common and therefore worth handling?

  4. 4.
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    Suppose the file corresponding to ip gets unlinked by another process between sys_link ’s calls to iunlock(ip) and dirlink. Will the link be created correctly? Why or why not?

  5. 5.
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    create makes four function calls (one to ialloc and three to dirlink) that it requires to succeed. If any doesn’t, create calls panic. Why is this acceptable? Why can’t any of those four calls fail?

  6. 6.
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    sys_chdir calls iunlock(ip) before iput(cp->cwd), which might try to lock cp->cwd, yet postponing iunlock(ip) until after the iput would not cause deadlocks. Why not?

  7. 7.
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    Implement the lseek system call. Supporting lseek will also require that you modify filewrite to fill holes in the file with zero if lseek sets off beyond f->ip->size.

  8. 8.
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    Add O_TRUNC and O_APPEND to open, so that > and >> operators work in the shell.

  9. 9.
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    Modify the file system to support symbolic links.

  10. 10.
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    Modify the file system to support named pipes.

  11. 11.
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    Modify the file and VM system to support memory-mapped files.