On Wed, Aug 24, 2011 at 05:18:57PM -0400, Alan Stern wrote:
> On Wed, 24 Aug 2011, Greg KH wrote:
>
> > 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.
>
> Yes, because the device file is held open by mkfs or fsck. You can
> test this easily enough, in a nondestructive way, by using this little
> shell script:
>
> echo -n 'Press RETURN to continue... '
> read </dev/tty
>
> Stick that in a file, and run the file with input redirected to the
> appropriate /dev/sd? file.
Ok, good, just wondering.
> > > @@ -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?
>
> It could be made to work that way. I had to choose, so I chose to make
> TRY_DISCONNECT work like DISCONNECT when the callback was missing.
> Doing it as you suggest might be better though, because then the user
> program could decide what to do if the kernel driver doesn't support
> TRY_DISCONNECT.
>
> What would be a good error code for that case? -EOPNOTSUPP? Or the
> traditional -ENOTTY?
-ENOTTY is the correct thing here.
> > I can't comment on the scsi layer, but what about devices that don't use
> > scsi? Like "raw" block drivers?
>
> You mean things like Pete Zaitcev's ub driver? They would need an
> equivalent change.
Ok, and if we return the correct error code, as shown above, if the
TRY_DISCONNECT was not there, then userspace could fall back on the
"what do I do now?" logic.
If you can get the scsi people to accept that part, I'll take the usb
portion, nice job.
greg k-h
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