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Subject: Re: [PATCH] devcoredump: increase the device delete timeout to 10
 mins
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Abhinav Kumar <quic_abhinavk@quicinc.com>,
        linux-kernel@vger.kernel.org
Cc:     rafael@kernel.org, linux-arm-msm@vger.kernel.org,
        dri-devel@lists.freedesktop.org, swboyd@chromium.org,
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Date:   Tue, 08 Feb 2022 22:54:34 +0100
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On Tue, 2022-02-08 at 13:40 -0800, Abhinav Kumar wrote:
> > 
> I am checking what usermode sees and will get back ( I didnt see an 
> error do most likely it was EOF ). I didnt follow the second part.

I think probably it got -ENODEV, looking at kernfs_file_read_iter().

> If the file descriptor read returns EOF, even if we consider them 
> separate how will it resolve this issue?
> 
> My earlier questions were related to fixing it in devcoredump to detect
> and fix it there. Are you suggesting to fix in usermode instead? How?
> 

Yeah, no, you cannot fix it in userspace.

But I just followed the rabbit hole down kernfs and all, and it looks
like indeed the read would be cut short with -ENODEV, sorry.

It doesn't look like there's good API for this, but it seems at least
from the underlying kernfs POV it should be possible to get_device() in
open and put_device() in release, so that the device sticks around while
somebody has the file open? It's entirely virtual, so this should be OK?

johannes