linux-kernel - Re: [PATCH 2/4] efivarfs: always register filesystem

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Message-ID: <Y8q7qz29QMfeNdMV@hovoldconsulting.com>
Date:   Fri, 20 Jan 2023 17:04:59 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Peter Jones <pjones@...hat.com>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Jeremy Kerr <jk@...abs.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] efivarfs: always register filesystem

On Fri, Jan 20, 2023 at 10:23:18AM +0100, Ard Biesheuvel wrote:
> (cc Peter, Heinrich)
> 
> On Thu, 19 Jan 2023 at 17:45, Johan Hovold <johan+linaro@...nel.org> wrote:
> >
> > The efivar ops are typically registered at subsys init time so that
> > they are available when efivarfs is registered at module init time.
> >
> > Other efivars implementations, such as Google SMI, exists and can
> > currently be build as modules which means that efivar may not be
> > available when efivarfs is initialised.
> >
> > Move the efivar availability check from module init to when the
> > filesystem is mounted to allow late registration of efivars.
> >
> > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> 
> I think this change is fine in principle, but I 'm not sure if there
> is user space code that the distros are carrying that might get
> confused by this: beforehand, efivarfs would not exist in
> /proc/filesystems and now, it will but trying to mount it might fail.

User space must already handle mount failing since commit 483028edacab
("efivars: respect EFI_UNSUPPORTED return from firmware") so that should
not be an issue.

Johan