Hey everyone, so I got a handful of positive responses to this. I've
replied to a few individuals already, but it's been a hectic week so I
haven't had a chance to reply to everyone yet. I just wanted to write
a quick note to let everyone know that I *will* get back to you this
weekend, and also a heads up that I already have two or three diffs in
my inbox now for this assignment. :)
I'll also try to think of more little tasks like this and try to
better organize them in the future.
Thanks everyone!
On Mon, Sep 19, 2011 at 9:56 AM, Matthew Dempsky wrote:
> Here's a small project for someone with basic C programming experience
> and an understanding of UNIX system calls (e.g., file descriptors and
> symbolic vs hard links). Thought I'd send it to tech@ first in case
> anyone's interested in working on it as a starter project.
>
> POSIX 2008 added two new flags for the ln(1) utility: -P and -L
> (http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html).
> See the spec for details, but the basic idea is that if you have a
> symbolic link "foo" pointing at "bar", then running "ln -L foo xyzzy"
> creates "xyzzy" as a new hard link to the file "bar" (i.e., the same
> as "ln foo xyzzy"), but running "ln -P foo xyzzy" instead creates
> "xyzzy" as a new hard link to the *symbolic link* "foo".
>
> To do this, you'll need to take advantage of the new linkat(2) system
> call (already supported by OpenBSD:
> http://www.openbsd.org/cgi-bin/man.cgi?query=linkat). The relevant
> new functionality for this project is that it accepts a flag argument
> to control whether to follow symbolic links or not when creating the
> hard link.
>
> I suggest creating some regression tests to check that your new code
> works and hasn't broken anything. (You can use lstat(2) to
> programmatically check that two directory entries refer to the same
> file by checking that their st_dev and st_ino fields are equal.)
>
> Finally, with some clever use of the new *at(2) functionality, you
> should be able to avoid doing any explicit string concatenation of
> path names. E.g., for "ln x/file1 y/file2 z/file3 path/to/dir",
> instead of calling:
>
>link("x/file1", "path/to/dir/file1");
>link("y/file2", "path/to/dir/file2");
>link("z/file3", "path/to/dir/file3");
>
> you should be able to do:
>
>int dirfd = open("path/to/dir", O_RDWR|O_DIRECTORY);
>linkat(AT_FDCWD, "x/file1", dirfd, "file1", AT_SYMLINK_FOLLOW);
>linkat(AT_FDCWD, "y/file2", dirfd, "file2", AT_SYMLINK_FOLLOW);
>linkat(AT_FDCWD, "z/file3", dirfd, "file3", AT_SYMLINK_FOLLOW);
>
> Feel free to privately contact me if you're interested and/or have any
> questions about this project.
