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

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Message-ID: <468c5651-6883-b6f1-64a4-6c6c2cade6de@intel.com>
Date:   Fri, 10 Aug 2018 12:14:32 -0700
From:   Tadeusz Struk <tadeusz.struk@...el.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        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 12:00 PM, James Bottomley wrote:
> On Fri, 2018-08-10 at 11:56 -0700, Tadeusz Struk wrote:
>> On 08/10/2018 11:48 AM, James Bottomley wrote:
>>> On Fri, 2018-08-10 at 11:21 -0700, Tadeusz Struk wrote:
>>>> 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.
>>>
>>> If the reason is to not create a wq unless it's needed, shouldn't
>>> the condition actually be first open with flag O_NONBLOCK?
>>>
>>
>> Not really because one can do:
>>
>> int fd = open("/dev/tpm0", O_RDWR);
>> fcntl(fd, F_SETFL, O_NONBLOCK);
> 
> so move the condition to first need to queue ...
> 

That would work, even though this is not how this is usually done.
The first open looks like the sweet spot between module init
and first need to queue.
Thanks,
-- 
Tadeusz