ICSI 333系统功能介绍

College of Engineering and Applied Sciences
Department of Computer Science
ICSI 333 – System Fundamentals, Spring 2022
Project 3
The total grade for the assignment is 100 points.
You must follow the programming and documentation guidelines (see file Programming Assignments
Requirements and Recommendations.docx).
Due date: 8:00 am on Monday, April 11, 2022.
Description
In this project, you must write a C program that performs the system actions – copying or moving a file
or a group of files to a specified path. The program acts differently depending on the usage:
• it performs copying if used as
copy source1 [source2 ...] destination
• it performs moving if used as
move source1 [source2 ...] destination
The source and destination names are full paths, and your program must be able to extract the file or
directory base name when needed.
When your program performs moving (not copying), it copies a file to the new location then deletes the
file (unlinks the old path). Physical coping of all bytes takes time; the more efficient way would be to
create a new link (the new path linked to the old bytes on a disk). And I suggest you try this way first, but
the OS may not let you do so for several reasons. So then go to the first plan.
You may need to study online resources and discuss the project with classmates. But you should not
borrow a solution online or from other students. It is better to skip some functionalities than to submit
a plagiarized code. Of course, you can always ask your TA and instructor for help.
To implement required usage, you need file multiple linking, for example,
gcc prog.c -o copy; ln copy move
After that, the file with the same executable code can be run under the two different names, and the
program itself decides on coping or moving depending on the name that the user used.
Keep in mind that there are two types of file links – hard and soft (or symbolic).
• Hard links (each file must have at least one): Files have names that people use and unique numbers
that the OS uses. The unique number (inode + device ID) corresponds to the physical collection of
bytes on a disk, and only the kernel manages such a number. File names are created by people. You
can give a name then change it. The OS links your name to a physical location of the collection of
bytes. Thus, a file name is linked to a unique number. You may have several file names linked to the
physical location (why you may need it is another story).
• Soft links (not a must-have): You may want to link a new file name to the existing file name (not to
the physical bytes). For example, to have an alias that you can delete later and not worry about
deleting the real file bytes. It is a soft link.
Once your program has decided on the required action (copying or moving), it must check the
destination:
• only a directory or device can be the destination for copying more than one file and
• only a directory can be the destination for moving more than one file.
An invalid destination must result in the error message and program termination. For this project, you
must understand and use the system call stat(). The following information adopted from
https://man7.org/linux/man-pa... will be helpful while detecting the file type.
The structure stat has the field stat.st_mode that contains the file type and mode. POSIX refers
to the stat.st_mode bits corresponding to the mask 01700001 as the file type, the 12 bits
corresponding to the mask 07777 as the file mode bits, and the least significant 9 bits (the mask 0777)
as the file permission bits.
The following mask values are defined for the file type:
S_IFMT 0170000 bit mask for the file type bit field
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
Thus, to test for a regular file (for example), one could write:
1 Note the number system used.
3
stat(pathname, &sb);
if ((sb.st_mode & S_IFMT) == S_IFREG) {
/ Handle regular file /
}
Because tests of the above form are common, additional macros are defined by POSIX to allow the test
to be written more concisely:
S_ISREG(m) //is it a regular file?
S_ISDIR(m) //directory?
S_ISCHR(m) //character device?
S_ISBLK(m) //block device?
S_ISFIFO(m) //FIFO (named pipe)?
S_ISLNK(m) //symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m) //socket? (Not in POSIX.1-1996.)
The preceding code snippet could thus be rewritten as:
stat(pathname, &sb);
if (S_ISREG(sb.st_mode)) {
/ Handle regular file /
}
Then your program must process each file to copy or move. If a source file does not exist, the error
message must be generated, and the next file must be tried.
To copy a file, you must use system calls that read and write big blocks (use BUFSIZ macro).
• A file should not be copied to itself.
• If the file with such a name already exists in the destination folder, permission for overwriting
should be asked.
To move a file, the first try should be linking it to the new path. If it does not work (because the OS may
block it or for another reason), you must copy this file and then delete the source.
• You can add this code to check why link does not work:
if( link( src, dst ) < 0 ){
printf( "Can't link to directory %s\n", dst );
perror( "link" );}
• Use unlinking for file deleting.
The program must output its actions.
Examples of program execution
% ./move
% Usage: move source1 [source2 ...] destination
% ./copy MyFile.c NextFile.c ../backups/
% MyFile.c NextFile.c succesefuly copied to ../backups
Submission, Grading, and Academic Integrity
The project must be submitted on Blackboard. You have three attempts; please read Programming
Assignments Requirements and Recommendations on Blackboard for suggested use of the attempts and
submission package.
Please read Programming Assignments Requirements and Recommendations on Blackboard for the
grading rubric.
Please read Programming Assignments Requirements and Recommendations on Blackboard for a strong
warning on cheating.