Re: [PATCH] usb: storage: skip only when uas driver is loaded

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jul 02, 2019 at 10:36:59AM +0800, JC Kuo wrote:
> On 7/1/19 4:52 PM, Greg KH wrote:
> > On Mon, Jul 01, 2019 at 04:48:48PM +0800, JC Kuo wrote:
> >> When usb-storage driver detects a UAS capable device, it ignores the
> >> device if CONFIG_USB_UAS is enabled. usb-storage driver assumes uas
> >> driver certainly will be loaded. However, it's possible that uas
> >> driver will not be loaded, for example, uas kernel module is not
> >> installed properly or it is in modprobe blacklist.
> >>
> >> In case of uas driver not being loaded, the UAS capable device will
> >> not fallback to work at Bulk-only-transfer mode. The device just
> >> disappears without any notification to user/userspace.
> >>
> >> This commit changes usb-storage driver to skip UAS capable device
> >> only when uas driver is already loaded to make sure the device will
> >> at least work with Bulk protocol.
> > 
> > But what happens if the driver is loaded afterward, because 'modprobe'
> > was called by the driver core (or it should have been, because this is a
> > device that supports that protocol)?
> If uas driver is loaded after usb-storage driver probed the device,
> the device will still work with Bulk-only protocol, though it can't
> make uses of streams.

Which is not a good thing, and is what the original code was there to
prevent happening.

> > I think you just broke working systems :(
> > 
> > Why wouldn't the UAS driver get loaded automatically if it is configured
> > in the system as it is today?
> An user might want to completely disable uas for some reason so he/she
> adds "blacklist uas" to modprobe conf file. I think in case of this,
> usb-storage driver has to enable this device with the legacy Bulk-only
> protocol instead of ignoring the device.

Why would they want to do that?  Where are people doing this in ways
that breaks their systems?

> As an alternative to this patch, I thought I could get uas driver
> loaded before usb-storage driver so I tried moving the functions in
> drivers/usb/storage/uas-detect.h into uas.c and letting usb-storage
> links uas_use_uas_driver() of uas.ko. However, that didn't work
> because uas driver actually depends on usb-storage driver for
> usb_stor_adjust_quirks(). There will be a recursive dependency.
> 
> Please let me know if there is better approach to avoid the issue.

If users blacklist the uas driver, that's their choice and they should
rebuild their kernel :)

Or better yet, talk to us to get the issue fixed for why they would want
to blacklist such a driver.

As it is, this patch is not acceptable.

thanks,

greg k-h