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Re: question about mach ports and fork

> Actually, only fork() and exec() invalidate the Mach ports. The current
> vfork() implementation actually arranges for the Mach task associated
> with the parent to be shared with the child (resulting in two procs
> running in one Mach task and having equal access to Mach resources like
> ports and VM). But it's only an implementation artifact and you
> shouldn't depend upon it. You must stick to the list of vfork()-safe
> APIs and behaviors (exec(), _exit(), not popping the stack, etc...) to
> assure continued operations regardless of the implementation.

I just tried that with my library and all of my IOUSBDeviceInterfaces
work with both the child and parent. I will have to keep that in mind. Its
too bad I can't rely on that because it is exactly what i need (and
expected from fork).

> There is no [guaranteed safe] way to re-validate them under the same
> port name with the same number of references (thus making the port
> names sprinkled throughout the process memory valid again). But there
> are some common techniques used to pass send rights to these ports from
> the parent to the child under a [randomly chosen] new name. And many
> of the frameworks allow for instantiation of objects passing an
> explicit port to use - rather than looking them anew. I'm not sure
> about IOService, however. You can't just open a new IOKit service
> connection in the child? This is sometimes impossible because the
> parent was privileged and the child not (so I feel your pain).

I have tried to open a new connection to iokit with the child process by
calling IOCreateMasterPort again but I get the same result as when I
didn't. The problem must lie in the IOService which looks like it keeps
trak of the master port used to open it. It would be a really simple fix
if i could rely on the programmer to call usb_open on a device after the
fork call (i think. i know there are a number of ports invalidated that I
don't really know about).

Thanks for your reply. I am just starting to get a handle on the mach/bsd
kernel used in darwin and how it differs from a traditional bsd kernel.


-Nathan
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References: 
 >question about mach ports and fork (From: "Nathan T. Hjelm" <email@hidden>)
 >Re: question about mach ports and fork (From: Jim Magee <email@hidden>)



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