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

On Tue, 31 Mar 2015 15:02:24 -0700
josh@joshtriplett.org wrote:

quoted

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.

The flag is fine, but, once we have set that flag saying we want those
messages, how do we know which type of structure we've gotten?  That's
the piece of the puzzle I'm missing, sorry if I'm being overly slow.

Thanks,

jon