2) For fork() support:
a) Extend mprotect() with PROT_DONTCOPY so processes can avoid copy-on-write problems.
b) (maybe someday?) Add a VM_ALWAYSCOPY flag and extend mprotect() with PROT_ALWAYSCOPY so processes can mark pages to be pre-copied into child processes, to handle the case where only half a page is registered.
I believe this puts the code that must be trusted into the kernel and gives userspace primitives that let apps handle the rest.
Do you plan to work with David Addison from Quadrics ? For sure, your hardware have very different capabilities. But ioproc_ops is a really nice solution and might help a lot when dealing with deregistration and fork.
For instance, instead of adding PROT_DONT/ALWAYSCOPY, you may use an ioproc hook in the fork path. This hook (a function in your driver) would be called for each registered page. It will decide whether the page should be pre-copied or not and update the registration table (or whatever stores address translations in the NIC). In addition, the driver would probably pre-copy cow pages when registering them.
It's nice to see these two works coming to LKML at the same time. It would be great if we could merge them and get a generic solution that's suitable to both registration based cards (IB/Myri/Ammasso) and MMU-based cards (Quadrics).
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