Re: anon unions are cool

[Albert Cahalan <acahalan@gmail.com>]

On 1/22/06, Kyle Moffett <mrmacman_g4@mac.com> wrote:
> On Jan 22, 2006, at 19:36, Albert Cahalan wrote:
> > For example, suppose we wanted to rename a badly-named struct
> > member. If the struct is used all over the kernel, this becomes a
> > giant project with huge potential for patch conflicts.
>
> Actually, pure struct-member renames are not that common, however it
> _is_ common to add an accessor method due to upcoming locking/
> virtualization changes or similar.  For that case (Using a random
> recent example from the list.  This was decided to not be the best
> route for pid virtualization, but it's just an example):
>
> struct task_struct {
>         [...]
>
>         pid_t pid;
>
>         [...]
> };

This case is rather interesting. At more than one place I've worked,
I found people assuming that the kernel's "pid" was a pid, when in
fact it is a tid. (a "task ID" or "thread ID") The confusion probably
leads to kernel bugs. I've seen many bugs related to this, though I
can't be 100% sure that they don't all involve code that existed prior
to the tgid concept.