Re: [Xenomai-core] Auto closing of file descriptors and fork.

[Jan Kiszka <jan.kiszka@domain.hid>]

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Gilles Chanteperdrix wrote:
> Gilles Chanteperdrix wrote:
>  > Hi,
>  > 
>  > I have a problem with auto closing of file descriptors and fork. I
>  > have an application (a modified pppd, to name it), which in a certain
>  > mode (pppd "updetach" mode) opens some real-time file descriptors,
>  > forks and exit the parent, continuing to use the file descriptors in
>  > the child. The problem is that when exiting the parent, file
>  > descriptors are automatically destroyed and therefore can not be used
>  > in the child.
>  > 
>  > Any ideas for a fix ?
> 
> More precisely. We need to trap the "fork" event, and handle it in the
> skins event callbacks. We will need to create a new ppd structure for
> the new process, but what will we do with the skin objects ? If we keep
> the same objects for the child and increment a reference count, we will
> end up with an object that need to be inserted in two per-process
> lists. If we create new objects, how will we manage for user-space
> references (inherited accross fork) to remain valid ?

The only way I see are process-private file descriptor tables +
reference counters for the underlying objects. On fork, the descriptor
table would be cloned and the reference counter of the contained object
would be incremented, creating another reference to them. Or should we
rather re-open those objects, creating another instance?

BTW, by adding a fork hook, my old idea of storing the ppd reference in
some I-pipe ptdkey comes into reach again.

Jan


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