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From:   Nicolas Boichat <drinkcat@chromium.org>
Date:   Wed, 3 Feb 2021 17:18:19 +0800
Message-ID: <CANMq1KAPe8F2WVsxYnP46Zx7K_0YSpnAUgod1WjenhOcHRk2kA@mail.gmail.com>
Subject: Re: [BUG] copy_file_range with sysfs file as input
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     "Darrick J. Wong" <djwong@kernel.org>,
        linux-fsdevel@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
        Amir Goldstein <amir73il@gmail.com>,
        Dave Chinner <dchinner@redhat.com>,
        Luis Lozano <llozano@chromium.org>,
        Ian Lance Taylor <iant@google.com>
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On Wed, Feb 3, 2021 at 5:04 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Mon, Jan 25, 2021 at 03:54:31PM +0800, Nicolas Boichat wrote:
> > Hi copy_file_range experts,
> >
> > We hit this interesting issue when upgrading Go compiler from 1.13 to
> > 1.15 [1]. Basically we use Go's `io.Copy` to copy the content of
> > `/sys/kernel/debug/tracing/trace` to a temporary file.
>
> Nit, the above file is NOT a sysfs file.  Odds are it is either a
> debugfs, or a tracefs file, please check your mounts to determine which
> it is, as that matters a lot on the kernel backend side for trying to
> figure out what is going on here :)

Yes yes it's tracefs ,-) But, from the other thread
https://lkml.org/lkml/2021/1/26/2029 sysfs (and any other fs that
generates files dynamically like procfs) would likely hit issues as
well (but maybe in more rare circumstances).

Thanks!

>
> thanks,
>
> greg k-h