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SubjectRe: RFC: ipath ioctls and their replacements
I've been flailing away at the ioctls in our driver, with a good degree
of success. However, one in particular is proving tricky:

> Opening the /dev/ipath special file assigns an appropriate free
> unit (chip) and port (context on a chip) to a user process.
> Think of it as similar to /dev/ptmx for ttys, except there isn't
> a devpts-like filesystem behind it. Once a process has
> opened /dev/ipath, it needs to find out which unit and port it
> has opened, so that it can access other attributes in /sys. To
> do this, we provide a GETPORT ioctl.

I still don't see how to replace this with anything else without
performing unnatural acts.

We use struct file's private_data to keep a pointer to the device in
use, which works fine for ioctl.

However, if I'm coming into the kernel over a netlink socket, I have no
obvious way of going from my table of devices to the processes that have
each one open, and I see no evidence that any other device driver tries
to do anything like this either.

Short of keeping a reference to the task_struct in the device, or
walking the sending process's file table if we receive a netlink message
(both of which are disgusting), I see no way to make this ioctl go away.

Am I missing something?


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