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Subject: [Bug 201611] [patch] Add devfs_get_cdevpriv_from_file(9)
Date: Tue, 22 Sep 2015 20:18:06 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=201611

--- Comment #6 from Andy Ritger <aritger@nvidia.com> ---
(In reply to John Baldwin from comment #5)

Thanks for looking at this, John.

If the ioctl called by Process A returned a new file descriptor, that
would be workable.  Though, the user-space code to use this would then
need to be a bit different between FreeBSD and other UNIX platforms: at
least on Linux, I'm not sure how straight-forward it would be to create
a new file descriptor within the kernel code that processes the ioctl.
We chose opening the file in user space, in order to create the fd,
as the least complex way to create it.

In process B, the resource that is being shared won't necessarily be
mmaped into the process's CPU virtual address space: sharing a resource
can mean other things, such as mapping into the GPU's (not CPU's virtual
address space).

Is there concern with looking up the cdevpriv from the struct file?

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