linux-kernel - Re: [PATCH v2] efi: Introduce EFI bootloader control driver

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Message-ID: <20160318161505.GU2619@codeblueprint.co.uk>
Date:	Fri, 18 Mar 2016 16:15:05 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Daniel Baluta <daniel.baluta@...el.com>
Cc:	linux-efi@...r.kernel.org, stefan.stanacar@...el.com,
	octavian.purdila@...el.com, linux-kernel@...r.kernel.org,
	matthew.k.gumbel@...el.com, mohamed.abbas@...el.com,
	constantin.musca@...el.com
Subject: Re: [PATCH v2] efi: Introduce EFI bootloader control driver

On Fri, 18 Mar, at 12:11:50PM, Daniel Baluta wrote:
> From: Matt Gumbel <matthew.k.gumbel@...el.com>
> 
> This driver intercepts system reboot requests and populates the
> LoaderEntryOneShot EFI variable with the user-supplied reboot
> argument. EFI bootloaders such as Gummiboot will consume this
> variable and use it to control which OS is booted next.
> 
> We use this with Android where reboot() tells the kernel that
> we want to boot into recovery or other non-default OS environment.
> 
> It is the bootloader's job to guard against this variable being
> uninitialzed or containing invalid data, and just boot normally
> if that is the case.
> 
> Signed-off-by: Matt Gumbel <matthew.k.gumbel@...el.com>
> Signed-off-by: Mohamed Abbas <mohamed.abbas@...el.com>
> Signed-off-by: Constantin Musca <constantin.musca@...el.com>
> Signed-off-by: Daniel Baluta <daniel.baluta@...el.com>
> ---
> Changes since v1:
> 	* updated Makefile after changing source name from efibc.c -> efi-bc.c
> 	to comply with naming rules in drivers/firmware/efi/
> 
>  drivers/firmware/efi/Kconfig  |  11 ++
>  drivers/firmware/efi/Makefile |   1 +
>  drivers/firmware/efi/efi-bc.c | 251 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 263 insertions(+)
>  create mode 100644 drivers/firmware/efi/efi-bc.c

Why does this require a driver? Why is it not possible to solve this
problem by creating the variable in userspace before invoking
reboot(2)?