linux-kernel - Re: [PATCH] tpm: add support for partial reads

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Date:   Mon, 23 Jul 2018 20:05:54 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Tadeusz Struk <tadeusz.struk@...el.com>
Cc:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: add support for partial reads

On Mon, Jul 23, 2018 at 04:42:38PM -0700, Tadeusz Struk wrote:
> On 07/23/2018 03:08 PM, Jason Gunthorpe wrote:
> > On Mon, Jul 23, 2018 at 03:00:20PM -0700, Tadeusz Struk wrote:
> >> On 07/23/2018 02:56 PM, Jason Gunthorpe wrote:
> >>> The proposed patch doesn't clear the data_pending if the entire buffer
> >>> is not consumed, so of course it is ABI breaking, that really isn't OK.
> >> The data_pending will be cleared by the timeout handler if the user doesn't
> >> read the response fully before the timeout expires. The is the same situation
> >> if the user would not read the response at all.
> > That causes write() to fail with EBUSY
> > 
> > NAK from me on breaking the ABI like this
> 
> What if we introduce this new behavior only for the non-blocking mode
> as James suggested? Or do you have some other suggestions?

I think you should do it entirely in userspace.

But something sensible linked to O_NONBLOCK could be OK.

Jason