代写CS 4323、代做Operating Systems、R编程设计调试、代写R代写

日期：2019-05-18 02:25

Programming Project 3

CS 4323 Operating Systems

Spring 2019

Instructor: Fred Wu Office: 215 e-mail: cnhengwu@gmail.com

Instructor Office Hours: 10:00 -12:00 PM on Monday and Wednesday

In this programming project, you are asked to implement a simplified version of the  find?

utility on Linux system. This assignment assists you for better understanding of file

systems design, how to use the Linux's system calls, and enhancing programming skills

and experience with programming on a Unix-like environment.

Description

The find utility is used to locate files on a Unix or Linux system. find will search any set

of directories you specify for files that match the supplied search criteria. You can search

for files by name, owner, group, type, permissions, date, and other criteria. The search is

recursive in that it will search all subdirectories too. The syntax looks like this:

$find where-to-look criteria what-to-do

Requirements

You need to implement the following functionalities. You can compare the output of your

program with the output of the standard find utility provided on Linux.

1. find where-to-look

2. find where-to-look criteria

a. find where-to-look -name <specified name>

b. find where-to-look -mmin <specified number of minutes>

c. find where-to-look -inum <specified i-node number>

3. find where-to-look criteria -delete

Extra credit:

4. find where-to-look criteria -exec command

Details of Each Functionality

1. find where-to-look

This will display the pathnames of all files in the specified directory and all

subdirectories. e.g. (if no directory specified, the default is the current working

directory)

$ find Document

You will get the output like:

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Document/file1

Document/file2

Document/subfolder/file3

2. find where-to-look criteria

2.1 find where-to-look -name <specified name>

This will search the specified directory (where-to-look) and all subdirectories for any

files named <specified name> and display their pathnames. e.g.

$ find Document –name foo

Here we are using the criterion -name with the argument foo to tell find to perform a

name search for the filename foo. The output might look like this:

Document/wpollock/foo

Document/ua02/foo

Document/foo

If find doesn't locate any matching files, it produces no output.

2.2 find where-to-look -mmin <specified number of minutes>

This will find those files modified with the specified number of minutes ago

You can specify a number “n” to mean exactly n, “-n” to mean less than n, and “+n”

to mean more than n.

$ find Document -mmin -10

This is used to locate files modified less than 10 minutes ago

2.3 find where-to-look -inum <specified i-node number>

Find a file that has i-node number n.

$ find Document -inum n

3. find where-to-look criteria -delete

This is an example of usage "find where-to-look criteria what-to-do". This will find

files with specified criteria and delete them; e.g.

$ find Document -name foo -delete

$ find Document -mmin -10 -delete

Extra credit:

4. find where-to-look criteria -exec command

This will find files with specified criteria and execute the specified command; e.g.

$ find Document -name foo -exec cat (this should find the file with a name “foo” in

the specified directory and output the content of the file by executing the “cat”

command on the file; this should be equivalent to “$ find Document -name foo -exec

cat {} \; ” on the Oak machine)

$ find Document -name foo -exec rm (this should find the file with a name “foo” in

the specified directory and delete the file; this should be equivalent to “$ find

Document -name foo -exec rm {} \; ” on the Oak machine)

3

$ find Document -name foo -exec mv <a new name> (this should find the file with a

name “foo” in the specified directory and rename to a new name; this should be

equivalent to “$ find Document -name foo -exec mv {} <a new name> \;” on the Oak

machine)

If you are able to implement and support the above three commands (cat, rm,

mv), you can score the extra credit.

Sample Codes and Hints

Before you start, you can create a testing directory under your home directory, this will

help you debugging your code and better understanding the routine of each function.

Follow the steps below to create a test directory:

Table 1, Create a Test Directory

After typing the above 18 commands in Table. 1, you will have a simple directory

structure.

Then, by typing:

you will get a tree of all the files, as shown in the below:

Figure 1. Tree structure of all the files in a directory

This is a typical directory structure in Linux file system. From the Fig.1, we can see that

there are files and subdirectory within a directory.Therefore you can imagine that the

find utility is probably a recursive routine.

But let?s see what we missed in a directory,

ls –al –R testdir

you will see something like:

jialin@jaln:~$ ls -al -R testdir/

testdir/:

total 24

drwxr-xr-x 4 jialin jialin 4096 2013-04-14 00:53 .

drwxr-xr-x 73 jialin jialin 12288 2013-04-14 01:50 ..

drwxr-xr-x 3 jialin jialin 4096 2013-04-14 00:52 dir1

drwxr-xr-x 2 jialin jialin 4096 2013-04-14 00:53 dir4

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:52 test1

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:52 test2

testdir/dir1:

total 12

drwxr-xr-x 3 jialin jialin 4096 2013-04-14 00:52 .

drwxr-xr-x 4 jialin jialin 4096 2013-04-14 00:53 ..

drwxr-xr-x 2 jialin jialin 4096 2013-04-14 00:53 dir2

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:52 test3

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:52 test4

testdir/dir1/dir2:

total 8

drwxr-xr-x 2 jialin jialin 4096 2013-04-14 00:53 .

drwxr-xr-x 3 jialin jialin 4096 2013-04-14 00:52 ..

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:53 test5

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:53 test6

testdir/dir4:

total 8

drwxr-xr-x 2 jialin jialin 4096 2013-04-14 00:53 .

drwxr-xr-x 4 jialin jialin 4096 2013-04-14 00:53 ..

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:53 test7

-rw-r--r-- 1 jialin jialin 0 2013-04-14 00:53 test8

Figure 2. All Contents in A Directory

Notice that there are some hidden files starting with . or ..

Be careful about that!

Studying the basic directory structure and the contents in a directory is a good start for

you to implement the find utility. The following code (Table 2) recursively prints all the

file names in a directory, you may need to learn and pick up some useful system calls

from the codes and then implement other find utilities.

0 /*

1 *A function that recursively print all file names

2 *Input: directory name, i.e., char * sub_dir

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3 *Output: all file names

4 */

5 void read_sub (char* sub_dir)

6 {

7 DIR *sub_dp=opendir(sub_dir);//open a directory stream

8 struct dirent * sub_dirp;//define

9 struct stat buf;//define a file status structure

10 char temp1[]=".";

11 char temp2[]="..";

12 char temp3[]="/";

13 if(sub_dp!=NULL)

14 //check whether the directory stream is opened successfully

15 {

16 // read one entry each time

17 while((sub_dirp=readdir(sub_dp))!=NULL)

18 {

19 //print the first entry, a file or a subdirectory

20 printf("%s\n",sub_dirp->d_name);

21

22 //check whether the first entry is a subdirectory

23 char * temp =sub_dirp->d_name;

24

25 //to avoid recursively searching . and .. in the directory.

26 if(strcmp(temp,temp1)!=0&&strcmp(temp,temp2)!=0)

27 {

28 char *temp_sub=temp3;

29 temp_sub=strcat(temp_sub,temp);

30 //now you add the / in front of the entry’s name

31 char* temp_full_path=malloc(sizeof(char)*2000);

32 temp_full_path=strcpy(temp_full_path,sub_dir);

33 strcat(temp_full_path,temp_sub);

34 //now you get a full path, e.g., testdir/dir1 or testdir/test1

35

36 // try to open

37 DIR * subsubdp=opendir(temp_full_path);

38 //if not null, means we find a subdirectory, otherwise, its just a file

39 if(subsubdp!=NULL){

40 //close the stream, because we will reopen it in the recursive call.

41 closedir(subsubdp);

42 read_sub(temp_full_path);//call the recursive function call.

43 }

44 }

45 }//end of while loop

46 closedir(sub_dp);//close the steam

47 }

48 else

49 {

50 printf("cannot open directory\n");

51 exit(2);

52 }

53 }

Table 2. Sample Codes for Printing All File Names

There are several system calls you need to know in your program.

1. DIR *opendir(const char *name) at line 7, 37

The opendir() function opens a directory stream corresponding to the directory name,

and returns a pointer to the directory stream. The stream is positioned at the first entry

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in the directory.

2. struct dirent *readdir(DIR *dirp) at line 17

The readdir() function returns a pointer to a ?dirent? structure representing the next

directory entry in the directory stream pointed to by ?dirp?. It returns NULL on

reaching the end of the directory stream or if an error occurred.

3. The ?dirent? structure defines a file system independent directory entry, which

contains information common to directory entries in different file system types. The

dirent structure is shown in Figure 3 as follows:

struct dirent {

ino_t d_ino; /* inode number */

off_t d_off; /* offset to the next dirent */

unsigned short d_reclen; /* length of this record */

unsigned char d_type; /* type of file; not supported

by all file system types */

char d_name[256]; /* filename */

};

Figure 3. Strucutre of Dirent

Note that we have used the d_name in the sample codes at line 20 and 23.

4. Another system call you need is stat()

int stat(const char *path, struct stat *buf);

This system call returns information about a file. No permissions are required on the

file itself.Stat is also a struct in Linux system. The structure of stat is shown in the

Figure 4:

struct stat {

dev_t st_dev; /* ID of device containing file */

ino_t st_ino; /* inode number */

mode_t st_mode; /* protection */

nlink_t st_nlink; /* number of hard links */

uid_t st_uid; /* user ID of owner */

gid_t st_gid; /* group ID of owner */

dev_t st_rdev; /* device ID (if special file) */

off_t st_size; /* total size, in bytes */

blksize_t st_blksize; /* blocksize for file system I/O */

blkcnt_t st_blocks; /* number of 512B blocks allocated */

time_t st_atime; /* time of last access */

time_t st_mtime; /* time of last modification */

time_t st_ctime; /* time of last status change */

};

Figure 4. Structure of Stat

Why do we need the stat() call and stat struct?Since you are required to implement a

find utility like

$ find where-to-look -inum <specified i-node number>

The stat contains the information of i-node and other needed stuff.

How to use it?Recallthat we have the path name in line 20, and we defined a file

status structure in line 9. Then to print the file size in bytes, we can use the following

codes:

struct stat buf;//define a file status structure

if(stat(sub_dirp->d_name,&buf)==0)

printf("%d ", (int)buf.st_size);

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Figure 5. Print File Status

5. Remove() will be needed

To implement the ?find where-to-look criteria –delete? function, you will need

remove():

remove(file_name);

6. For parsing options and arguments, you can directly manipulate argv, or you can

consider using getopt()/getopt_long()/argp_parse() supplied by the GNU C library. A

sample code getopt.c is provided as an example of showing how getopt() is used. You

can always Google to find more details of these command line options and arguments

parsing functions.

Expected Submission:

You should submit a single tarball/zipped file through the Blackboard containing the

following:

Source codes

Output files for your test cases

Grading Criteria:

Grade Criteria

10 Inline comments to briefly describe your code

20 Implement the find where-to-look?

30 Implement the find where-to-look criteria?

20 Implement the find where-to-look criteria -delete?

10 (extra

credit)

Implement the find where-to-look criteria -exec command?

20 Correctness of result. Source code can be compiled and executed.

Reference Materials:

Linux system programming:

Book: Linux System Programming

Online:

Tutorial for Beginners, http://www.ee.surrey.ac.uk/Teaching/Unix/

Advanced Linux Programming, http://www.advancedlinuxprogramming.com/alpfolder/advanced-linux-programming.pdf

Linux man pages, http://linux.die.net/man/

Stackoverflow, http://stackoverflow.com/

Codewiki, http://codewiki.wikidot.com/start

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