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

[Andrei Borzenkov]

14.10.2015 11:00, Ye, Ting пишет:
> Could you please describe the details how does GRUB use UEFI network protocols?

When efinet driver is loaded it enumerates handles with SNP; these 
handles represent network cards for grub. If driver is part of initial 
core.img (default for network boot image) it additionally queries loaded 
image handle for PXE for DhcpAck using EFI_PXE_BASE_CODE_PROTOCOL and is 
using it for autoconfiguration. Before the first send/receive request on 
network card SNP on associated handle is opened exclusively and SNP 
Transmit/Receive are used.

> I see the thread says that EXCLUSIVE open SNP causes PXE boot fail.
>
> If you read below description about 'EXCLUSIVE' in UEFI specification, you will 
> find when GRUB exclusive opens SNP protocol, the UEFI will remove any drivers 
> that opened SNP with BY_DRIVER by calling the driver's Stop() function. In UEFI 
> network stack, MNP driver will open SNP 'BY_DRIVER'. So if GRUB/iPXE exclusive 
> opens SNP, MNP will uninstall itself and the whole UEFI network stack is 
> disconnected except SNP and UNDI. Hence, the UEFI PXE no longer work.
>
>
> > > 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.
>
>
> If GRUB would like to call SNP protocol only, it should use EXCLUSIVE open to 
> gain the exclusive access and disconnect UEFI network stack since MNP. Then the 
> MNP background polling is also disabled.

It does it already.

> If GRUB still needs UEFI PXE capability, it should utilize PXE base code 
> protocol to continue the process, rather than calling SNP, as SNP is already 
> consumed by UEFI network stack.

It does not use PXE after initial autoconfiguration as described above 
nor does it need it. All data transmission is performed using SNP only.

> Thanks,
> Ye Ting
>
>
> -----Original Message-----
> From: edk2-devel [mailto:address@hidden On Behalf Of Andrei Borzenkov
> Sent: Wednesday, October 14, 2015 2:58 PM
> To: Ye, Ting; Laszlo Ersek; address@hidden; address@hidden
> Cc: edk2-devel-01; Mark Salter; address@hidden; address@hidden; address@hidden
> Subject: Re: [edk2] [grub PATCH] efinet: disable MNP background polling
>
> 14.10.2015 09:15, Ye, Ting пишет:
> > May I know the details what problems it causes in some cases?
>
> One is being discussed in this thread:
>
> http://lists.gnu.org/archive/html/grub-devel/2015-10/msg00013.html
> http://lists.gnu.org/archive/html/grub-devel/2015-10/msg00068.html
>
> Another was reported recently:
>
> http://lists.gnu.org/archive/html/help-grub/2015-09/msg00033.html
> http://lists.gnu.org/archive/html/grub-devel/2015-10/msg00071.html
>
>
> > Thanks,
> > Ye Ting
> >
> > -----Original Message-----
> > From: Andrei Borzenkov [mailto:address@hidden
> > Sent: Wednesday, October 14, 2015 1:58 PM
> > To: Ye, Ting; Laszlo Ersek; address@hidden; address@hidden
> > Cc: address@hidden; edk2-devel-01; address@hidden; address@hidden; Mark Salter
> > Subject: Re: [edk2] [grub PATCH] efinet: disable MNP background polling
> >
> > 14.10.2015 08:19, Ye, Ting пишет:
> > > 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.
> >
> > That is exactly what grub currently does - it opens SNP exclusively.
> > Apparently it is causing problems in some cases.
>
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