Re: [PATCH v2 0/7] CLONE_FD: Task exit notification via file descriptor

On Tue, Mar 31, 2015 at 10:08:07PM +0200, Jonathan Corbet wrote:

So I finally got around to having a look at this, and one thing caught my
eye:

quoted

             read(2) (and similar)
                     When  the  new  process  exits,  reading  from  the  file
                     descriptor produces a single clonefd_info structure:

                     struct clonefd_info {
                         uint32_t code;   /* Signal code */
                         uint32_t status; /* Exit status or signal */
                         uint64_t utime;  /* User CPU time */
                         uint64_t stime;  /* System CPU time */
                     };

This would appear to assume that a clonefd_info structure is the only
thing that will ever be read from this descriptor.  It seems to me that
there is the potential for, someday, wanting to be able to read and write
other things as well.  Should this structure be marked with type and
length fields so that other structures could be added in the future?

I don't think it makes sense for a caller to get an arbitrary structure
on read(), and have to figure out what they got and ignore something
they don't understand.  Instead, I think it makes more sense for the
caller to say "Hey, here's a flag saying I understand the new thing, go
ahead and give me the new thing".  So, for instance, if you want to
receive SIGSTOP/SIGCONT messages for child processes through this
descriptor, we could add a flag for that.

- Josh Triplett