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

From: Daniel Kiper
Subject: Re: [edk2] [grub PATCH] efinet: disable MNP background polling
Date: Wed, 14 Oct 2015 13:08:47 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

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 
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 
this is huge overhaul, so, we should think twice before choosing that way.


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