Extend File Descriptor (Extra)

Make your pintos to support closing of stdin, stdout and dup2 system call in linux

The closing the fd of stdin and stdout is forbidden in current implementation of pintos. In this extra point requirements, you first allow user to close stdin and stdout as same as the linux. That is, the process should never read the inputs if you close stdin, and the process should never print out anything if you close stdout.

Next, implement the dup2 system call.

int dup2(int oldfd, int newfd);

The dup2() system call creates a copy of the file descriptor oldfd with the file descriptor number specified in newfd, and returns newfd on success. If the file descriptor newfd was previously open, it is silently closed before being reused.

Note the following points:

• If oldfd is not a valid file descriptor, then the call fails (returns -1), and newfd is not closed.

• If oldfd is a valid file descriptor, and newfd has the same value as oldfd, then dup2() does nothing, and returns newfd.

After a successful return from this system call, the old and new file descriptors may be used interchangeably. Although they are different file descriptors, they refer to the same open file description and thus share file offset and status flags; for example, if the file offset is modified by using seek on one of the descriptors, the offset is also changed for the other.

Note that duped file descriptors must preserve their semantic after the forking.

YOU SHOULD PASS ALL TESTCASES FOR EXTRA TO GET THE CREDIT. TAKE ALL OR NOTHING.