Re: [edk2] [grub PATCH] efinet: disable MNP background polling

From: Seth Goldberg <seth.goldberg@oracle.com>
To: The development of GNU GRUB <grub-devel@gnu.org>
Cc: "Ye, Ting" <ting.ye@intel.com>,
	edk2-devel-01 <edk2-devel@ml01.01.org>,
	"arvidjaar@gmail.com" <arvidjaar@gmail.com>,
	"glin@suse.com" <glin@suse.com>, Mark Salter <msalter@redhat.com>,
	Laszlo Ersek <lersek@redhat.com>
Subject: Re: [edk2] [grub PATCH] efinet: disable MNP background polling
Date: Wed, 14 Oct 2015 08:39:12 -0700	[thread overview]
Message-ID: <1BAD7DA9-D60E-4743-9143-3327989DF6B6@oracle.com> (raw)
In-Reply-To: <20151014110847.GQ6226@olila.local.net-space.pl>

> On Oct 14, 2015, at 4:08 AM, Daniel Kiper <daniel.kiper@oracle.com> wrote:
> 
>> On Wed, Oct 14, 2015 at 05:19:32AM +0000, Ye, Ting wrote:
>> Hi all,
>> 
>> If I understand the issue correctly, I don't quite agree that UEFI
>> spec is imprecise about SNP constraints described as following.
>> The "constraint" described here is that the grub should use attribute
>> "EXCLUSIVE" to open SNP protocol to gain exclusive access. This usage
>> is clearly described in page 184, chapter 6.3 EFI_BOOT_SERVICES.OpenProtocol().
>> 
>> EXCLUSIVE        Used by applications to gain exclusive access to a protocol interface.
>>            If any drivers have the protocol interface opened with an attribute of BY_DRIVER,
>>            then an attempt will be made to remove them by calling the driver's Stop() function.
>> 
>> The grub code should not assume that the SNP is not occupied by other
>> drivers, instead, it should use EXCLUSIVE to open SNP protocol, or to
>> be more precise, use OpenProtocolInformation() to check whether SNP is
>> already opened by other driver, then decide whether need to use EXCLUSIVE
>> to disconnect the other drivers. This is the typical usage for all UEFI
>> protocol, not particular constraints to SNP protocol.
> 
> Looks good! Great! However, it looks that we still have a problem if somebody
> opens SNP in EXCLUSIVE mode. Then GRUB2 SNP open will fail according to UEFI spec.
> Sadly we do not have a control on other stuff and one day our approach may fail
> because somebody decided to open SNP in EXCLUSIVE mode in e.g. a driver. Does
> it mean that migration to MNP is one sensible solution for our problems? As I know
> this is huge overhaul, so, we should think twice before choosing that way.

   Then it is fortunate that when I wrote the MNP implementation that we ship with Oracle Solaris 11.2, that I tested it on many thousands of systems as well as on new UEFI implementations at the UEFI Plugfest ;).

  --S

> 
> Daniel
> 
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