Bug#516258: ITP: ozerocdoff -- temporarily disables ZeroCD
Hi Henrique,
Sorry for top-posting, I CC Aurélien and Didier as they are dealing with
usb-modeswitch which plays the same role as ozerocdoff hence leave your
full answer below.
Thanks for your help and explanations. I think we can work with both
Aurélien and Didier to fill these bugs. If we can avoid using userspace
utilities (be it rezero, oozerocdoff or usb-modeswitch), that would
indeed be great, but do you think kernel developers will agree to
completely de-activate CD emulation possibilities? Don't you think they
**might** have a use for Linux users in the future?
Again, many thanks!
Julien
Le samedi 21 février 2009 à 10:30 -0300, Henrique de Moraes Holschuh a
écrit :
> On Sat, 21 Feb 2009, Julien Valroff wrote:
> > Le vendredi 20 février 2009 à 21:54 -0300, Henrique de Moraes Holschuh a
> > écrit :
> > > On Fri, 20 Feb 2009, Julien Valroff wrote:
> > > > The new USB Option WWAN modem device support a CDROM device, which holds
> > > > the needed Windows driver to use the WWAN modem.
> > > >
> > > > Therefore the firmware of the WWAN modem announce during the USB enumeration
> > > > process to work as a virtual CDROM device with its vendor name "ZOPTION".
> > > >
> > > > This device is now called ZERO-CD.
> > > >
> > > > ozerocdoff is a solution to switch off the ZERO-CD and allow the modem to
> > > > be a modem.
> > >
> > > Why is it needed? Are there devices that malfunction as modems while the
> > > emulated cdrom is active?
> >
> > Yes.
> >
> > > I ask because I have tested a bunch of Huawei E226, which do have this
> > > stupid cdrom emulation hack from hell to bypass Windows security policies.
> > > While option does allow it to register the mass storage device with
> > > usb-storage, it also works as a GSM modem just fine at the same time...
> >
> > That is not the case of (at least) Option WWAN modems.
>
> Fair enough.
>
> > > If there is a pressing need to disable that stupid emulated cdrom, maybe a
> > > bug should be filled to fix it right in the kernel, so that the emulated
> > > device is never bound to usb-storage to begin with?
> >
> > I attach the original README file shipped with ozerocdoff, which
> > explains much better than I could.
>
> [... ozerocdoff readme below ...]
>
> > The Linux OS does currently not use this ZERO-CD, because the image can
> > not hold all the needed binary kernel drivers, which
>
> And it never will, it is just plain impossible. Source it could hold, but
> that's useless from a normal user perspective, so it is a completely useless
> feature for Linux, and it can be unconditionally disabled on all WWAN modems
> (not just "Option WWAN"), IMO.
>
> That makes it the kernel's business. I am not against Debian adding these
> userspace utilities, mind you (so I am not against your ITP), they will be
> needed for at least one year...
>
> > it off. Once you send this switch off command to the WWAN modem, another
> > new USB enumeration will be requested by the WWAN modem firmware.
> > Afterwards the real WWAN modem interface is available on the USB bus.
>
> That's the clinch, then. It only becomes usable after the cdrom emulator is
> disabled, so the kernel driver is incomplete if it doesn't do it (again,
> IMO).
>
> > Looking on the Linux USB core system, it has another restriction. If there
> > are more than one possible drivers, which can work successfully with that
> > USB WWAN modem, the USB core system will allow probing the WWAN modem by
> > these drivers in a special order. First the already loaded driver will be
> > allowed to do the probe. If then this driver do a successful probe,
> > another potential driver will never become a chance to do also a probing
> > with that hardware. Therefore it is (currently) impossible to use the
> > final WWAN modem driver to send the ZERO-CD switch off command, because
> > often the USB mass storge driver will be already loaded and is working in
> > your Linux system. If the probing of an already loaded module is not
> > successful or no module is loaded, the udev system will trigger a
> > modeprobe to load the needed driver(s). But the loading order of the
> > drivers is not clear specified, although is may depends on the order of
> > the appearance in the modules dependency files created by depmod.
>
> This is a kernel deficiency, and it can and should be fixed (if it isn't
> already by adding quirks to the option module or whatever).
>
> > But this probe order is also important to know for some old Option WWAN
> > modems, which could be handled by the mainstream 'option' kernel driver.
> > Unfortunately this is a bug, because the mainstream 'option' driver looks
> > on the wrong USB device ID.
>
> This should also be fixed in the kernel, and appears to be a consequence of
> the stuff above.
>
> > The ZERO-CD switch off command is simple a SCSI 'rezero' command. The
> > easiest way to send this command to the WWAN modem is by using the
> > standard Linux USB mass storage driver. Because the WWAN modem will
> > initiate a hard disconnect from the SCSI bus connection after receiving
> > that rezero command and the USB mass storage driver is not prepared for
> > such a situation, we risk a possible system freeze. Therefore we use a
>
> This is ALSO a kernel bug that needs to be fixed, unless "a hard disconnect"
> is something that violates some spec, which I very much doubt, since SCSI is
> supposed to support target-initiated disconnection.
>
> [...]
>
> > Solution use the correct HSO Option driver:
> >
> > Because we have now two drivers for some Option WWAN-modems, we simply
> > blacklist the mainstream 'option' kernel module driver, which we do not
> > like to use. Note that this 'option' driver does support only Option WWAN
> > modem with Version 3 Interface, which support only virtual serial modem
> > ports. The new 'hso' driver supports the newer Version 4 Interface. Here
> > also an IP network device is available, which allow high speed
> > communication also by using the slow USB 1.1 bus system. Note also that
> > this network interface is not identical to a virtual ethernet, because it
> > "speaks" only IP. So e.g. running a dhcpclient is here not possible,
> > because this would require the support of the simple ether transport
> > package frames. The 'option' mainstream driver can be prevent to be
> > automatically loaded be adding a line like: blacklist option
>
> Again, stuff that needs to be fixed in the kernel properly.
>
> You can file a bug on bugzilla.kernel.org, mentioning this mailinglist
> thread, AND attaching the ozerocdoff README (make it clear that it explains
> the hoops that are being done to get that hardware to work).
>
> You need two bugs: one for the "usb-storage might freeze on a SCSI hard
> disconnect from an "Option WWAN Modem with an emulated CDROM mass-storage
> device", and the other for the rest of the stuff dealing with the "option"
> module not doing the right thing to *select* the proper module to drive the
> "Option WWAN modem".
>
> Or you can file the two bugs against the Debian kernel, tag them upstream,
> and ask the Debian kernel maintainers to forward it upstream (write THAT on
> the top of the bug reports, or someone might thing by mistake that the
> upstream tag means you have already forwarded it upstream, etc).
>
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