linux-kernel - Re: [PATCH 1/6] fs: Add flag to file_system

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Date:   Fri, 12 Feb 2021 08:46:53 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     "Darrick J . Wong" <djwong@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ian Lance Taylor <iant@...gle.com>,
        Luis Lozano <llozano@...omium.org>,
        Dave Chinner <david@...morbit.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] fs: Add flag to file_system_type to indicate content
 is generated

On Fri, Feb 12, 2021 at 12:44:00PM +0800, Nicolas Boichat wrote:
> Filesystems such as procfs and sysfs generate their content at
> runtime. This implies the file sizes do not usually match the
> amount of data that can be read from the file, and that seeking
> may not work as intended.
> 
> This will be useful to disallow copy_file_range with input files
> from such filesystems.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> ---
> I first thought of adding a new field to struct file_operations,
> but that doesn't quite scale as every single file creation
> operation would need to be modified.

Even so, you missed a load of filesystems in the kernel with this patch
series, what makes the ones you did mark here different from the
"internal" filesystems that you did not?

This feels wrong, why is userspace suddenly breaking?  What changed in
the kernel that caused this?  Procfs has been around for a _very_ long
time :)

thanks,

greg k-h