Re: vfork thoughts

[Andrew Cagney <cagney@redhat.com>]

Phil Muldoon wrote:
> I've bee reading about vfork challenges for the past week. Here are my 
> thoughts.
>
> Mark when he fixed an issue related to breakpoints I think 
> crystallized the issue with vfork in this thread:
>
> http://article.gmane.org/gmane.comp.monitoring.frysk.general/1072
>
> While at first the issue of breakpoints might seem to be nothing to do 
> with vfork(), it is very relevant. Literature suggests that the use of 
> vfork for any purpose other than an immediate prelude to an exec call 
> is not advisable. However, there could - and probably are - examples 
> of where this is not the case. Also as detailed in Mark's email this 
> makes the usage of breakpoints troublesome, as child and parent share 
> memory.
Totally agree.
>
> If we model vfork transparently though the fork observer then there is 
> a danger of the user (be that an actual user, or an api call) assuming 
> that the it is a true fork and not a vfork. Is it more sensible to 
> model a completely separate set of observers to model vfork? This way, 
> if there are breakpoints set in the child (and therefore the parent) 
> we can uninstall them after the child execs. However this approach 
> burdens the state machine with additional states that would 
> essentially duplicate the fork states. Is the replication of code to 
> deal with the vfork specific issues warranted here?
>
> If anyone has a real life use case for debugging a vfork scenario we 
> could model, that would help also.

Perhaps look at the fork/daemon code.  It uses a vfork, followed by a 
fork, followed by an exec.  Stepping through that would be way cool!

>
> Regards
>
> Phil
>
>