linux-kernel - Re: RFC: Add USBDEVFS_TRY

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Date:	Wed, 24 Aug 2011 13:45:33 -0700
From:	Greg KH <greg@...ah.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Hans de Goede <hdegoede@...hat.com>,
	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: RFC: Add USBDEVFS_TRY_DISCONNECT ioctl

On Wed, Aug 24, 2011 at 04:32:31PM -0400, Alan Stern wrote:
> Okay, here's a sample patch.  Actually it's three patches, listed one 
> after another, but people can apply it like a single patch.
> 
>      1.	Introduce the USBDEVFS_TRY_DISCONNECT ioctl and the check_busy
> 	callback it uses.  Implement the callback in the usbfs driver; 
> 	this gives a way for programs to unbind kernel drivers without
> 	unbinding other userspace drivers.
> 
>      2.	Implement device-file reference tracking in the SCSI layer,
> 	and the device_open and device_close callbacks it uses.

Does this handle if the filesystem is being created or fscked, as it's
not mounted at that time.

> @@ -1647,9 +1653,16 @@ static int proc_ioctl(struct dev_state *
>  	else switch (ctl->ioctl_code) {
>  
>  	/* disconnect kernel driver from interface */
> +	case USBDEVFS_TRY_DISCONNECT:
>  	case USBDEVFS_DISCONNECT:
>  		if (intf->dev.driver) {
>  			driver = to_usb_driver(intf->dev.driver);
> +			if (ctl->ioctl_code == USBDEVFS_TRY_DISCONNECT &&
> +					driver->check_busy) {
> +				retval = driver->check_busy(intf);
> +				if (retval)
> +					break;
> +			}

I don't like the fact that if a driver doesn't contain check_busy() then
it will automatically fall back to looking like it was a DISCONNECT
call, which could give userspace a false sense of "everything was fine"
when trying this out.

Why not fail if that callback is not present?


I can't comment on the scsi layer, but what about devices that don't use
scsi?  Like "raw" block drivers?

thanks,

greg k-h
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