Re: [RFC PATCH 3/4] Implement driver for supporting multiple emulated TPMs

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Fri, Jan 22, 2016 at 10:09:16AM -0500, Stefan Berger wrote:
> Ok, so I guess the ioctl would take the PID of the created child as a
> parameter (how else to identify it?). The kernel would find that child,
> check that the calling parent is indeed the parent of the child, and if
> everything looks good do the hook-up.

That is one choice, it is worth reviewing what, eg, the net folks did
for their API. They have already thought about this alot.

> >Right, controlfd implies that only vtpms could be shared to a IMA
> >namespace, which is a terrible API. This is another reason why
> >reserved is a terrible API.
> 
> Thanks for all feedback. I will eventually post v2. For now it's to be found
> here:
> 
> https://github.com/stefanberger/linux
> 
> The branch is easy to find.

That looks much nicer, yes.

I'd also merge the tpm-vtpm.h into the .c file

However, I'm still not sure this is right:

+	vtpm_dev->chip = tpmm_chip_alloc(&vtpm_dev->dev, &vtpm_tpm_ops);

The only issue is error unwind, the tpmm version assumes devm works
for that, but the vtpm_dev will not be destroyed if the tpm attach
fails, do devm is not appropriate.

As I said before the tpmm stuff was a hack I did to make it easier to
migrate the large number of drivers, core code should not be relying
on devm like that... One good option here would be unwind that a bit
and create a tpm_chip_alloc/tpm_chip_register flow that did not use
devm at all. That could be fairly straight forward..

Also, what is up with the _vtpm prefix on some functions? That doesn't
seem aligned with the kernel style..

And confused why there is a miscdev and a alloc_chrdev_region ?

Jason

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