linux-kernel - Re: [PATCH v4 2/2] tpm: add support for nonblocking operation

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Date:   Fri, 10 Aug 2018 11:21:14 -0700
From:   Tadeusz Struk <tadeusz.struk@...el.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     flihp@...bit.us, jgg@...pe.ca, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] tpm: add support for nonblocking operation

On 08/10/2018 10:43 AM, Jarkko Sakkinen wrote:
>> +static struct workqueue_struct *tpm_dev_wq;
> A naming contradiction with tpm_common_read() and tpm_common_write(). To
> sort that up I would suggest adding a commit to the patch set that
> renames these functions as tpm_dev_common_read() and
> tpm_dev_common_write() and use the name tpm_common_dev_wq here.
> 

Currently we have: tpm_open(), tpm_write(), tpm_release() in tpm-dev.c
tpmrm_open(), tpmrm_read(), tpmrm_write(), tpmrm_release() in tpmrm-dev.c
tpm_common_open(), tpm_common_read(), tpm_common_write(), tpm_common_release() in tpm-dev-common.c

I think that's pretty consistent. Do you want me to rename all of them to tpm_dev_*()?
I don't see any value in doing this. What about if I just rename: 
tpm_dev_wq_lock to tpm_common_wq_lock, and tpm_dev_wq to tpm_common_wq?

>> +static DEFINE_MUTEX(tpm_dev_wq_lock);
> This is an unacceptable way to do it, Rather add:
> 
> int __init  tpm_dev_common_init(void)
> {
> 	tpm_dev_common_wq = alloc_workqueue("tpm_dev_wq", WQ_MEM_RECLAIM, 0);
> 	if (!tpm_dev_common_wq)
> 		return -ENOMEM;
> 
> 	return 0;
> }
> 
> and call this in the driver initialization.
> 
That was the way it was implemented in v1 https://patchwork.kernel.org/patch/10442125/

See: static int __init tpm_dev_common_init(void)

and the feedback I got from Jason was:

"I wonder if it is worth creating this when the first file is
opened.. Lots of systems have TPMs but few use the userspace.."

so I changed this to allocate the WQ on first open. I think it makes sense,
but I leave it to you to decide.

Tadeusz,
-- 
Tadeusz