Here's what's happening: the dkms build process actually works from prl_mod.tar.gz, not the already expanded source. Recommend doing the following:
> su [enter root password]
> cd /usr/src/parallels-tools-12.1.3.41532/
> nano prl_fs/SharedFolders/Guest/Linux/prl_fs/inode.c [make your edits and save it]
> mv prl_mod.tar.gz prl_mod.tar.gz.old [just so the original doesn't get destroyed and you have to go back]
> tar cvpf prl_mod.tar . [create the initial tarball, then gzip it...]
> gzip prl_mod.tar [this will create the new prl_mod.tar.gz containing your edits]
> dkms build parallels-tools/12.1.3.41532
> dkms install parallels-tools/12.1.3.41532
Yeah, it's a kind of screwy way of going about things, but I'm sure there's a good reason for it somewhere.
Incidentally that's a Linux kernel module thing, not Parallels.
> su [enter root password]
> cd /usr/src/parallels-tools-12.1.3.41532/
> nano prl_fs/SharedFolders/Guest/Linux/prl_fs/inode.c [make your edits and save it]
> mv prl_mod.tar.gz prl_mod.tar.gz.old [just so the original doesn't get destroyed and you have to go back]
> tar cvpf prl_mod.tar . [create the initial tarball, then gzip it...]
> gzip prl_mod.tar [this will create the new prl_mod.tar.gz containing your edits]
> dkms build parallels-tools/12.1.3.41532
> dkms install parallels-tools/12.1.3.41532
Yeah, it's a kind of screwy way of going about things, but I'm sure there's a good reason for it somewhere.
Incidentally that's a Linux kernel module thing, not Parallels.

