linux-kernel - Re: access efi variables

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Message-ID: <20130917154630.GG3409@console-pimps.org>
Date:	Tue, 17 Sep 2013 16:46:30 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Arend van Spriel <arend@...adcom.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Matt Fleming <matt.fleming@...el.com>,
	linux-efi@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: access efi variables

On Sat, 14 Sep, at 07:01:19PM, Arend van Spriel wrote:
> On 09/14/13 00:37, H. Peter Anvin wrote:
> >On 09/13/2013 08:37 AM, Arend van Spriel wrote:
> >>I need to obtain a uefi variable so I went looking at the API in
> >>include/linux/efi.h. I found the following definition:
> >>
> >>But according to the specs the variable I need to obtain is 2k bytes.
> >>Should I expect trouble :-p
> >>
> >
> >efivarfs doesn't have those limitations.
> 
> Thanks, Peter
> 
> Looking into efivarfs it seems to use the functions that I looked at
> in efi.h so I guess I am misinterpreting the 1024 bytes limitation
> in the comment (either that or you are mistaken ;-) ). I need to
> access the variable from within a device driver so using efivarfs
> does not feel like the way to go here.

Look at how efivarfs_file_read() is implemented, e.g. using
efivar_entry_get(). In particular, note how it kmalloc()'s a buffer for
reading the variable data into, thereby avoiding any 1024-byte
limitation.

-- 
Matt Fleming, Intel Open Source Technology Center
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