How to disable ata driver on Hyper-V

[Hongjiang Zhang]

Hi Scott,

FreeBSD on Hyper-V already has a customized ata driver, which returns "BUS_PROBE_DEFAULT" or "EXNIO" for enabling or disabling the driver on ata controller. But this implementation has issues. If the ata controller has a CD/DVD device on it, the /dev/cd0 device failed to be created if I put CD/DVD on an ata controller which has been disabled.

What I want is disable the /dev/ada device but bypass the /dev/cd device. I found it is difficult for me to determine what type of device will be created in my customized ata probe function. That is why I want to disable ata driver.

Thanks
Hongjiang Zhang

-----Original Message-----
From: Scott Long [mailto:scott4long at yahoo.com] 
Sent: Thursday, August 18, 2016 12:22 AM
To: Hongjiang Zhang <honzhan at microsoft.com>
Cc: freebsd-scsi at freebsd.org
Subject: Re: How to disable ata driver on Hyper-V

Hi,

There’s no direct way to disable a specific driver or specific instance of a driver.  There are ways to disable a particular PCI function, but I’m not sure if that’s what you want.  Are you looking to override the default ata driver with your own custom driver?  The way to do that is have your custom driver provide a higher priority return code from its dev_probe routine.  The way this works is that positive return codes indicate an error.  Negative return codes indicate a priority, with the numbers closer to zero being a higher priority.  Zero is the highest priority, but should be used only with great care.  The priority for the default ahci driver is BUS_PROBE_DEFAULT, which resolves to (-20).  You might consider using BUS_PROBE_VENDOR, which resolves to (-10).  By having your driver look at the PCI bus:device:function tuple, you can selectively override the default driver for specific hardware.

Scott

> On Aug 17, 2016, at 2:49 AM, Hongjiang Zhang via freebsd-scsi <freebsd-scsi at freebsd.org> wrote:
> 
> Hi all,
> 
> I'm want to disable the default ata driver for FreeBSD on Hyper-V. How to do that?
> 
> Thanks
> Hongjiang Zhang
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