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Matej Focko
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Allow showing ‹last updated› on the pages and also rename the files where necessary, so they are shown in the order they were created. Signed-off-by: Matej Focko <mfocko@redhat.com>
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169 lines
No EOL
4.9 KiB
Markdown
---
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slug: garbage_collect
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title: Practice exam B
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description: |
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Garbage everywhere…
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last_update:
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date: 2023-05-08
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---
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# Garbage Collection
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:::caution Exam environment
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* During the exam you will be provided with a barebone _exam session_ on the
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_faculty computers_.
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* In browser you are only allowed to have the following tabs open:
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* [C documentation](https://en.cppreference.com)
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* page containing the assignment
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* You **are not** allowed to use your own source code, e.g. prepared beforehand
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or from the seminars.
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* You have **5 minutes** to read through the assignment and ask any follow-up
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questions should be there something unclear.
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* You have **60 minutes** to work on the assignment, afterward your work will be
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discussed with your seminar tutor.
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:::
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You have gotten into a trouble during your regular upgrade of your archLinux[^1]
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installation… You've been carelessly running the upgrades for months and forgot
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about clearing up the caches.
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Your task is to write a program `garbage_collect` that will evaluate the shell
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history provided as a file and will try to find files or directories that are
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suspiciously big and decide which of them should be deleted to free some space.
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## Format of the shell history
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You are provided one file consisting of the captured buffer of the terminal. You
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can see only two commands being used:
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1. `cd ‹somewhere›` that changes the current working directory.
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At the beginning you start in the root of the filesystem (i.e. `/`).
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You are **guaranteed** that `‹somewhere›` is:
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* `.` that is a current working directory (i.e. does nothing),
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* `..` that moves you up one level (in case you are in `/`, does nothing), or
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* is a valid directory in the current working directory.
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:::caution
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There are no guarantees or restrictions on the names of the files or
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directories!
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:::
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1. `ls` that will list files in the current working directory and their
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respective sizes. If there is a directory in the current working it has `dir`
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instead of the size.
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```
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$ ls
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dir a
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14848514 b.txt
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8504156 c.dat
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dir d
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$ cd a
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$ cd .
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$ cd .
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$ cd .
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$ ls
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dir e
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29116 f
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2557 g
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62596 h.lst
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$ cd e
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$ ls
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584 i
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$ cd ..
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$ cd ..
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$ cd d
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$ ls
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4060174 j
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8033020 d.log
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5626152 d.ext
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7214296 k
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```
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For this input, you will get following file system:
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```
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- / (dir, size=48381165)
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- a (dir, size=94853)
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- e (dir, size=584)
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- i (file, size=584)
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- f (file, size=29116)
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- g (file, size=2557)
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- h.lst (file, size=62596)
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- b.txt (file, size=14848514)
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- c.dat (file, size=8504156)
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- d (dir, size=24933642)
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- j (file, size=4060174)
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- d.log (file, size=8033020)
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- d.ext (file, size=5626152)
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- k (file, size=7214296)
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```
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## Format of the output
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Your program should support 2 switches:
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* `-gt ‹min_size›` that will print out suspiciously big files.
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* `-f ‹total_size› ‹min_unused›` that will print out a file to be deleted.
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### `-gt ‹min_size›`
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With this switch you are provided one additional argument:
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* `min_size` that is the lower bound (inclusive) for size of any file or
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directory that is supposed to be listed.
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When your program is being run with this switch, it is is supposed to print out
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all files **and** directories that are bigger than the provided `min_size`.
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### `-f ‹total_size› ‹min_unused›`
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With this switch you are provided two additional arguments:
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* `total_size` that is a total size of the filesystem[^2].
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* `min_unused` that is a minimum of free space required for an upgrade.
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Your program should find **exactly one** file or a directory that is of the
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smallest size, but big enough to free enough space for the upgrade to proceed.
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In other words, if that file or directory is deleted, following should hold:
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$$
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\mathtt{total\_size} - \mathtt{used} \geq \mathtt{min\_unused}
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$$
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## Example usage
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You can have a look at the example usage of your program. We can run your
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program from the shell like
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$ ./garbage_collect shell_history.txt -gt 10000000
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24933642 /d
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14848514 /b.txt
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48381165 /
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$ ./garbage_collect shell_history.txt -f 70000000 30000000
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24933642 /d
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## Requirements and notes
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* Define **structures** (and **enumerations**, if applicable) for the parsed
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information from the files.
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* For keeping the “records”, use some **dynamic** data structure.
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* Don't forget to consider pros and cons of using _specific_ data structures
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before going through implementing.
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* You **are not required** to produce 1:1 output to the provided examples, they
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are just a hint to not waste your time tinkering with a user experience.
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* If any of the operations on the input files should fail,
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**you are expected to** handle the situation _accordingly_.
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* Failures of any other common functions (e.g. functions used for memory
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management) should be handled in **the same way** as they were in the
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homeworks and seminars.
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* Your program **must free** all the resources before exiting.
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[^1]: Also applies to Fedora, but… we use arch btw :wink:
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[^2]: duh! |