UCLA Assignment5-System Call Programming and Debugging Solved

Assignment 5. System call programming and debugging
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Useful pointers
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-   Adam Aviv, [I/O System Calls](https://www.usna.edu/Users/cs/aviv/classes/ic221/s18/units/04/unit.html) (2018)
-   [The Open Group Base Specifications Issue 7, IEEE Std 1003.1-2008, 2016 Edition](http://www.opengroup.org/onlinepubs/9699919799/) is the official standard for commands, system calls and some higher-level library calls.
-   man strace
-   [strace](http://en.wikipedia.org/wiki/Strace) on Wikipedia

Laboratory: Buffered versus unbuffered I/O
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As usual, keep a log in the file lab.txt of what you do in the lab so that you can reproduce the results later. This should not merely be a transcript of what you typed: it should be more like a true lab notebook, in which you briefly note down what you did and what happened.

For this laboratory, you will implement transliteration programs tr2b and tr2u that use buffered and unbuffered I/O respectively, and compare the resulting implementations and performance. Each implementation should be a main program that takes two operands from and to that are byte strings of the same length, and that copies standard input to standard output, transliterating every byte in from to the corresponding byte in to. Your implementations should report an error from and to are not the same length, or if from has duplicate bytes. To summarize, your implementations should like the standard utility [tr](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/tr.html) does, except that they have no options, characters like [, - and \\ have no special meaning in the operands, operand errors must be diagnosed, and your implementations act on bytes rather than on (possibly multibyte) characters.

1.  Write a C transliteration program tr2b.c that uses [getchar](http://www.opengroup.org/onlinepubs/9699919799/functions/getchar.html) and [putchar](http://www.opengroup.org/onlinepubs/9699919799/functions/putchar.html) to transliterate bytes as described above.
2.  Write a C program tr2u.c that uses [read](http://www.opengroup.org/onlinepubs/9699919799/functions/read.html) and [write](http://www.opengroup.org/onlinepubs/9699919799/functions/write.html) to transliterate bytes, instead of using getchar and putchar. The nbyte arguments to read and write should be 1, so that the program reads and writes single bytes at a time.
3.  Use the strace command to compare the system calls issued by your tr2b and tr2u commands (a) when copying one file to another, and (b) when copying a file to your terminal. Use a file that contains at least 5,000,000 bytes.
4.  Use the [time](http://www.opengroup.org/onlinepubs/9699919799/utilities/time.html) command to measure how much faster one program is, compared to the other, when copying the same amount of data.

Homework: Encrypted sort revisited
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Rewrite the sfrob program you wrote previously so that it uses system calls rather than \<stdio.h\ to read standard input and write standard output. If standard input is a regular file, your program should initially allocate enough memory to hold all the data in that file all at once, rather than the usual algorithm of reallocating memory as you go. However, if the regular file grows while you are reading it, your program should still work, by allocating more memory after the initial file size has been read.

Your program should do one thing in addition to sfrob. If given the -f option, your program should ignore case while sorting, by using the standard [toupper](http://pubs.opengroup.org/onlinepubs/9699919799/functions/toupper.html) function to upper-case each byte after decrypting and before comparing the byte. You can assume that each input byte represents a separate character; that is, you need not worry about [multi-byte encodings](https://en.wikipedia.org/wiki/Variable-width_encoding). As noted in its specification, toupper's argument should be either EOF or a nonnegative value that is at most UCHAR\_MAX (as defined in [\<limits.h\](http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html)); hence one cannot simply pass a char value to toupper, as char is in the range CHAR\_MIN..CHAR\_MAX.

Call the rewritten program sfrobu. Measure any differences in performance between sfrob and sfrobu using the time command. Run your program on inputs of varying numbers of input lines, and estimate the number of comparisons as a function of the number of input lines.

Also, write a shell script sfrobs that uses standard [tr](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/tr.html) and [sort](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sort.html) to sort encrypted files using a pipeline (that is, your script should not create any temporary files, and should sort based on decrypted values just as sfrobu does). Your shell script should also accept an -f option, with the same meaning as with sfrobu. Use the time command to compare the overall performance of sfrob, sfrobu, sfrobs, sfrobu -f, and sfrobs -f.