linux-kernel - Re: [PATCH] efi/efivars: Create efivars mount point in the registration of efivars abstraction

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Date:   Thu, 24 Sep 2020 11:51:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Lee, Chun-Yi" <jlee@...e.com>, Ard Biesheuvel <ardb@...nel.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Fabian Vogt <fvogt@...e.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Arthur Heymans <arthur@...ymans.xyz>,
        Patrick Rudolph <patrick.rudolph@...ements.com>
Subject: Re: [PATCH] efi/efivars: Create efivars mount point in the
 registration of efivars abstraction

On Thu, Sep 24, 2020 at 04:28:33PM +0800, Lee, Chun-Yi wrote:
> This patch moved the logic of creating efivars mount point to the
> registration of efivars abstraction. It's useful for userland to
> determine the availability of efivars filesystem by checking the
> existence of mount point.

Why not do what all other tools do, and look in /proc/filesystems?

Why is efivars "special" in this way?  What tool isn't properly looking
for the filesystem in that way today?

> The 'efivars' platform device be created on generic EFI runtime services
> platform, so it can be used to determine the availability of efivarfs.
> But this approach is not available for google gsmi efivars abstraction.

I do not understand this last sentence, can you try to explain it
better?

> This patch be tested on Here on qemu-OVMF and qemu-uboot.

How about real hardware?  :)

> 
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: Matthias Brugger <mbrugger@...e.com>
> Cc: Fabian Vogt <fvogt@...e.com>
> Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Arthur Heymans <arthur@...ymans.xyz>
> Cc: Patrick Rudolph <patrick.rudolph@...ements.com>
> Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>
> ---
>  drivers/firmware/efi/efi.c  |  7 -------
>  drivers/firmware/efi/vars.c | 17 +++++++++++++++++
>  2 files changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 3aa07c3b5136..23c11a2a3f4d 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -405,13 +405,6 @@ static int __init efisubsys_init(void)
>  	if (error)
>  		goto err_remove_group;
>  
> -	/* and the standard mountpoint for efivarfs */
> -	error = sysfs_create_mount_point(efi_kobj, "efivars");
> -	if (error) {
> -		pr_err("efivars: Subsystem registration failed.\n");
> -		goto err_remove_group;
> -	}
> -
>  	if (efi_enabled(EFI_DBG) && efi_enabled(EFI_PRESERVE_BS_REGIONS))
>  		efi_debugfs_init();
>  
> diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> index 973eef234b36..6fa7f288d635 100644
> --- a/drivers/firmware/efi/vars.c
> +++ b/drivers/firmware/efi/vars.c
> @@ -1179,6 +1179,8 @@ int efivars_register(struct efivars *efivars,
>  		     const struct efivar_operations *ops,
>  		     struct kobject *kobject)
>  {
> +	int error;
> +
>  	if (down_interruptible(&efivars_lock))
>  		return -EINTR;
>  
> @@ -1191,6 +1193,19 @@ int efivars_register(struct efivars *efivars,
>  
>  	up(&efivars_lock);
>  
> +	/* and the standard mountpoint for efivarfs */
> +	if (efi_kobj) {

Why test for this?  Can it race?

thanks,

greg k-h