linux-kernel - Re: [PATCH] efi: add efivars kobject to efi sysfs folder

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Date:	Thu, 04 Oct 2012 09:54:35 +0100
From:	Matt Fleming <matt.fleming@...el.com>
To:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	glin@...e.com, "Lee, Chun-Yi" <jlee@...e.com>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Matthew Garrett <mjg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Peter Jones <pjones@...hat.com>
Subject: Re: [PATCH] efi: add efivars kobject to efi sysfs folder

On Thu, 2012-10-04 at 10:24 +0800, Lee, Chun-Yi wrote:
> UEFI variable filesystem need a new mount point, so this patch add
> efivars kobject to efi_kobj for create a /sys/firmware/efi/efivars
> folder.
> 
> Cc: Matt Fleming <matt.fleming@...el.com>
> Cc: Jeremy Kerr <jeremy.kerr@...onical.com>
> Cc: Matthew Garrett <mjg@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
> ---
>  drivers/firmware/efivars.c |   11 +++++++++++
>  include/linux/efi.h        |    1 +
>  2 files changed, 12 insertions(+), 0 deletions(-)

Jeremy, did you want to pick this up as part of your series?

Actually, shouldn't the new filesystem be called "efivarfs", or "efifs"
to make it more explicit that it is a filesystem?

We also need something in Documentation/filesystems/ describing the old
EFI variable method, why it's no longer any good, and why the new
filesystem is favoured. Does anybody have anything to add to the
following?

diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX
index 8c624a1..ddf5a83 100644
--- a/Documentation/filesystems/00-INDEX
+++ b/Documentation/filesystems/00-INDEX
@@ -38,6 +38,8 @@ dnotify_test.c
 	- example program for dnotify
 ecryptfs.txt
 	- docs on eCryptfs: stacked cryptographic filesystem for Linux.
+efivars.txt
+	- info for the efivars filesystem.
 exofs.txt
 	- info, usage, mount options, design about EXOFS.
 ext2.txt
diff --git a/Documentation/filesystems/efivars.txt b/Documentation/filesystems/efivars.txt
new file mode 100644
index 0000000..4350c1a
--- /dev/null
+++ b/Documentation/filesystems/efivars.txt
@@ -0,0 +1,16 @@
+
+efivars - a (U)EFI variable filesystem
+
+The efivars filesystem was created to address the shortcomings of
+using entries in sysfs to maintain EFI variables. The old sysfs EFI
+variables code only supported variables of up to 1024 bytes. This
+limitation existed in version 0.99 of the EFI specification, but was
+removed before any full releases. Since variables can now be larger
+than a single page, sysfs isn't the best interface for this.
+
+Variables can be created, deleted and modified with the efivars
+filesystem.
+
+The efivars filesystem is typically mounted like this,
+
+	mount -t efivars none /sys/firmware/efi/efivars


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