The Linux Kernel, CDDL and Related Issues

I don't think I'm understanding this passage correctly. Or if I am understanding it correctly, I'm not sure I see the logic. How is this passage intended to be interpreted?

I think it's saying that if a user space program has an API that allows plugins to be written, the plugins should be considered derivative works of the main program. Thus if the main program is distributed under a standard copyright, any 3rd-party plugin is copyright infringing in the absence of specific licensing to allow it.

Is this true? If anyone would know it would be Eben, but this seems at odds with the purpose of such an API. On the other hand, "As with any such interface ... we can assume ... that the overwhelming preponderance ... can be assumed to fall within the scope of the copyleft" doesn't sound like the sort of precise legal prose Eben normally writes.

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 
    AuthorDate: Wed May 15 20:23:06 2013 -0400
    Commit:     Al Viro 
    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 
    ...
    +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 
    AuthorDate: Wed Aug 7 08:53:45 2013 -0400
    Commit:     Brian Behlendorf 
    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;
    +}