HW8
released: 12/8, 9:00

> Answer the following questions.
> Submit your answers to Canvas assignments. There is an entry for this homework.
> 
> 
> CS5600 File System (fs5600)
> 
> These questions are intended to reinforce fs5600.
> 
> 
> 1. Suppose fs5600 has a file "/dir1/dir2/file1".
>    When a process read the file's information, namely executing:
>    """
>      struct stat;
>      fs_getattr("/dir1/dir2/file1", &stat)
>    """
> 
>    Question:
>    How many block reads ("block_read") does fs5600 perform? And what are they?
>    (assume buffer-cache is empty, meaning you have to read information from disk)
> 

[Answer:
  7
  read root inode
  read root data
  read dir1 indoe
  read dir1 data
  read dir2 indoe
  read dir2 data
  read file1 inode

  note: no need to read bitmap or file1's data because this is "fs_getatt"
  which only reads (so no need to touch bitmap) and only reads file metadata
  (so no need to touch file data blocks).
]


> 
> 
> 2. Suppose fs5600 has a file "/file1" and the file has 16KB of contents.
>    When a process read 4KB from offset 2KB, namely executing:
> 
>    """
>    char buf[4096];
>    fs_read("/file1", buf, 4096, 2048, NULL);
>    """
> 
>    Question:
>    How many block reads ("block_read") does fs5600 perform? And what are they?
>    (assume buffer-cache is empty, meaning you have to read information from disk)
> 

[ Answer:
  5
  read root inode
  read root data
  read file1 inode
  read file1 data[0]
  read file1 data[1]
]

> 
> 
> 3. Suppose a new file system fs5600+ has an inode as follows:
> 
>   """
>   struct fs_inode2 {
>       uint16_t uid;
>       uint16_t gid;
>       uint32_t mode;
>       uint32_t ctime;     /* time of last file status change */
>       uint32_t mtime;     /* time of last data modification */
>       int32_t  size;
>       uint32_t ptrs[1018];
>       uint32_t indirect_ptr; /* inode = 4096 bytes */
>   };
>   """
> 
>   And the "indirect_ptr" is the indirect pointer in a Unix inode.
>   It points to a block (4KB) that contains pointers (uint32_t) to actual data blocks.
> 
>   Questions:
> 
>   (a) how many pointers can one block store?
> 
>   (b) how many data block pointers in total (including both direct and indirect ones)
>       can an fs5600+ inode have?
> 
>   (c) what's the maximum file size of an fs5600+ file?

[
Answer:

(a)
4096 / 4 = 1024

(b)
(1024+1018)

(c)
(1024+1018) * 4KB
]