The Linux Kernel, CDDL and Related Issues (softwarefreedom.org)

Well, in May 2013, Al Viro committed code to Linux to add several new "KBIs", dir_emit and related functions (in include/linux/fs.h, which does not have a license block):

    commit 5f99f4e79abc64ed9d93a4b0158b21c64ff7f478
    Author:     Al Viro <viro@zeniv.linux.org.uk>
    AuthorDate: Wed May 15 20:23:06 2013 -0400
    Commit:     Al Viro <viro@zeniv.linux.org.uk>
    CommitDate: Sat Jun 29 12:46:48 2013 +0400

    [readdir] switch dcache_readdir() users to ->iterate()
    
    new helpers - dir_emit_dot(file, ctx, dentry), dir_emit_dotdot(file, ctx),
    dir_emit_dots(file, ctx).
    
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    ...
    +static inline bool dir_emit(struct dir_context *ctx,
    +                           const char *name, int namelen,
    +                           u64 ino, unsigned type)
    +{
    +       return ctx->actor(ctx, name, namelen, ctx->pos, ino, type) == 0;
    +}
    +static inline bool dir_emit_dot(struct file *file, struct dir_context *ctx)
    +{
    +       return ctx->actor(ctx, ".", 1, ctx->pos,
    +                         file->f_path.dentry->d_inode->i_ino, DT_DIR) == 0;
    +}
    +static inline bool dir_emit_dotdot(struct file *file, struct dir_context *ctx)
    +{
    +       return ctx->actor(ctx, "..", 2, ctx->pos,
    +                         parent_ino(file->f_path.dentry), DT_DIR) == 0;
    +}
    +static inline bool dir_emit_dots(struct file *file, struct dir_context *ctx)
    +{
    +       if (ctx->pos == 0) {
    +               if (!dir_emit_dot(file, ctx))
    +                       return false;
    +               ctx->pos = 1;
    +       }
    +       if (ctx->pos == 1) {
    +               if (!dir_emit_dotdot(file, ctx))
    +                       return false;
    +               ctx->pos = 2;
    +       }
    +       return true;
    +}

    commit 0f37d0c8bed442dd0d2c1b1dddd68653fa6eec66
    Author:     Richard Yao <ryao@gentoo.org>
    AuthorDate: Wed Aug 7 08:53:45 2013 -0400
    Commit:     Brian Behlendorf <behlendorf1@llnl.gov>
    CommitDate: Thu Aug 15 16:19:07 2013 -0700

        Linux 3.11 compat: fops->iterate()
    ...
        Compatibility with older kernels was accomplished by adding
        versions of the trivial dir_emit* helper functions.
    ...
    +static inline bool
    +dir_emit(struct dir_context *ctx, const char *name, int namelen,
    +    uint64_t ino, unsigned type)
    +{
    +       return ctx->actor(ctx->dirent, name, namelen, ctx->pos, ino, type) == 0;
    +}
    +
    +static inline bool
    +dir_emit_dot(struct file *file, struct dir_context *ctx)
    +{
    +       return ctx->actor(ctx->dirent, ".", 1, ctx->pos,
    +           file->f_path.dentry->d_inode->i_ino, DT_DIR) == 0;
    +}
    +
    +static inline bool
    +dir_emit_dotdot(struct file *file, struct dir_context *ctx)
    +{
    +       return ctx->actor(ctx->dirent, "..", 2, ctx->pos,
    +           parent_ino(file->f_path.dentry), DT_DIR) == 0;
    +}
    +
    +static inline bool
    +dir_emit_dots(struct file *file, struct dir_context *ctx)
    +{
    +       if (ctx->pos == 0) {
    +               if (!dir_emit_dot(file, ctx))
    +                       return false;
    +               ctx->pos = 1;
    +       }
    +       if (ctx->pos == 1) {
    +               if (!dir_emit_dotdot(file, ctx))
    +                       return false;
    +               ctx->pos = 2;
    +       }
    +       return true;
    +}

I agree entirely. But are you arguing that, in general when a program Z links to a library L to run, it is not important for the license of Z and the license of L to both permit it? A conclusion like this eviscerates all Copyleft licenses, so I am loathe to accept it.

I have harped on the close relationship between the organization of zfsonlinux's zfs.git and the linux kernel in multiple threads, because the core claim coming from Canonical is that the code in zfs.git is somehow essentially independent of the linux kernel. They do not articulate what this means or how we can determine whether it's the case in general. So far no definition I've considered seems to paint zfsonlinux in the same light that canonical have claimed.

(1) Torwalds is one of the people able to drum up the OSS community. If people hated him so much as to not follow him on a technical detail, they'd develop for BSD rather than Linux.

(2) the reason GPLv3 has mostly failed seems to be mostly due to the controversial nature of the changes while the change for more compatibility with another free license seems straightforward