操作系统练习-第6章文件管理

一. 多选题（共2题，50分）

1. (多选题, 25分)What would happen if the bitmap or free list containing the information about free disk blocks was completely lost due to a crash? Is there any way to recover from this disaster, or is it bye-bye disk? Discuss your answers for UNIX and the FAT-16 file system separately.

• A. In the FAT file system, the problem cannot occur because there is no free list.
• B. It is not a serious problem at all.
• C. But even if there were, all that would have to be done to recover it is to scan the FAT looking for free entries.
• D. In UNIX this can be done by scanning all the i-nodes.
• E. Repair is straightforward; it just takes time. The recovery algorithm is to make a list of all the blocks in all the files and take the complement as the new free list.

我的答案: ABCDE

2. (多选题, 25分)Name one advantage of hard links over symbolic links and one advantage of symbolic links over hard links.

• A. Hard links do not require any extra disk space, just a counter in the i-node to keep track of how many there are. Symbolic links need space to store the name of the file pointed to.
• B. Symbolic links can point to files on other machines, even over the Internet. Hard links are restricted to pointing to files within their own partition.
• C. None of the above answers are correct.
• D. Symbolic links do not require any extra disk space, just a counter in the i-node to keep track of how many there are. Hard links need space to store the name of the file pointed to.
• E. Hard links can point to files on other machines, even over the Internet. Symbolic links are restricted to pointing to files within their own partition.

我的答案: AB

二. 填空题（共2题，50分）

3. (填空题, 15分)How many disk operations are needed to fetch the i-node for a file with the path name /usr/ast/courses/os/handout.t? Assume that the i-node for the root directory is in memory, but nothing else along the path is in memory. Also assume that all directories fit in one disk block.

我的答案：10

4. (填空题, 35分)A UNIX file system has 4-KB blocks and 4-byte disk addresses. If i-nodes contain 10 direct entries, and one single, double, and triple indirect entry each, the maximum file size is (      )TB(      )GB(      )MB(      )KB(      )B.

我的答案：(1) 4             (2) 4                    (3) 4                   (4) 40                   (5) 0