Make an un-device?

Make an un-device?

[Tom Horsley]

Usually people want to know how to make udev recognize
devices. I have a device that is recognized just fine, but
I'd really like to declare it an un-device. I don't
want any /dev/ files created for it, I don't want the
driver loaded unless something else needs it. I want
it to disappear from creation completely.

Can custom udev rules do this?

Specifically, the device is the incredibly annoying fake CD
drive that appears along side my usb hard disk
when I plug it in.

Re: Make an un-device?

[David Zeuthen]

On Wed, 2010-03-24 at 12:43 -0400, Tom Horsley wrote:
> Usually people want to know how to make udev recognize
> devices. I have a device that is recognized just fine, but
> I'd really like to declare it an un-device. I don't
> want any /dev/ files created for it, I don't want the
> driver loaded unless something else needs it. I want
> it to disappear from creation completely.
> 
> Can custom udev rules do this?

Not specifically - ignore_device used to do something like this but we
removed that directive from udev... and even if we still had the
ignore_device directive, suppressing events at the udev level is wrong..
and that's why we removed ignore_device.

> Specifically, the device is the incredibly annoying fake CD
> drive that appears along side my usb hard disk
> when I plug it in.

One way to make such annoying drives disappear in GNOME and some other
desktop environments is to set the UDISKS_PRESENTATION_HIDE (or if you
are on an older distro than F13 vintage, it's called
DKD_PRESENTATION_HIDE) udev property like e.g. this

http://cgit.freedesktop.org/udisks/tree/data/80-udisks.rules#n188

Another way to solve this is adding an entry to something like one of
the unusual_* files under drivers/usb/storage in the kernel... but that
includes recompiling the kernel.

HTH,
David

Re: Make an un-device?

[Kay Sievers]

On Wed, Mar 24, 2010 at 17:43, Tom Horsley <horsley1953@gmail.com> wrote:
> Usually people want to know how to make udev recognize
> devices. I have a device that is recognized just fine, but
> I'd really like to declare it an un-device. I don't
> want any /dev/ files created for it, I don't want the
> driver loaded unless something else needs it. I want
> it to disappear from creation completely.
>
> Can custom udev rules do this?
>
> Specifically, the device is the incredibly annoying fake CD
> drive that appears along side my usb hard disk
> when I plug it in.

Udev can't really do anything here.

In many cases there are tools available from the disk vendor to
disable the fake cd drive.

Kay

Re: Make an un-device?

[Tom Horsley]

On Wed, 24 Mar 2010 13:07:52 -0400
David Zeuthen wrote:

> One way to make such annoying drives disappear in GNOME and some other
> desktop environments is to set the UDISKS_PRESENTATION_HIDE (or if you
> are on an older distro than F13 vintage, it's called
> DKD_PRESENTATION_HIDE) udev property like e.g. this

Yea, I found that, but it has already changed three times now
(first you used hal, then you used DKD, now you use UDISK).
I figured a lower level eradication might stick through
more changes :-).

Having some user configurable way to utterly hide devices
does seem useful. I recall having a "helpful" operating
system "upgrade" all the partitions on a disk once, thus
rendering it utterly useless in the multi-boot environment
that could boot older kernels.

Re: Make an un-device?

[Paul Fox]

tom wrote:
 > On Wed, 24 Mar 2010 13:07:52 -0400
 > David Zeuthen wrote:
 > 
 > > One way to make such annoying drives disappear in GNOME and some other
 > > desktop environments is to set the UDISKS_PRESENTATION_HIDE (or if you
 > > are on an older distro than F13 vintage, it's called
 > > DKD_PRESENTATION_HIDE) udev property like e.g. this
 > 
 > Yea, I found that, but it has already changed three times now
 > (first you used hal, then you used DKD, now you use UDISK).
 > I figured a lower level eradication might stick through
 > more changes :-).

in addition, the wouldn't the solution then apply to "all" desktops,
instead of "GNOME and some other" desktops?

given how often this comes up, i think it would be very useful
for there to be a page fully describing the reasons that the udev
project thinks the feature is a bad idea.  when i asked in
november for the reasons behind not being able to hide devices, i
got somewhat vague reasons.  (and i'm clearly still not
convinced. :-)  simply stating "suppressing events at the udev
level is wrong" isn't terribly compelling.

paul

 > 
 > Having some user configurable way to utterly hide devices
 > does seem useful. I recall having a "helpful" operating
 > system "upgrade" all the partitions on a disk once, thus
 > rendering it utterly useless in the multi-boot environment
 > that could boot older kernels.
 > --
 > To unsubscribe from this list: send the line "unsubscribe linux-hotplug" in
 > the body of a message to majordomo@vger.kernel.org
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=---------------------
 paul fox, pgf@laptop.org

Re: Make an un-device?

[David Zeuthen]

On Wed, 2010-03-24 at 13:52 -0400, Paul Fox wrote:
> given how often this comes up, i think it would be very useful
> for there to be a page fully describing the reasons that the udev
> project thinks the feature is a bad idea.  when i asked in
> november for the reasons behind not being able to hide devices, i
> got somewhat vague reasons.  (and i'm clearly still not
> convinced. :-)  simply stating "suppressing events at the udev
> level is wrong" isn't terribly compelling.

I'm sorry that you don't find this compelling but it came directly from
both myself and the udev maintainer (Kay Sievers) - you are free to
check the archives for better explanations. Or if you examine, in
detail, how uevents and libudev work, you will eventually understand why
ignore_device was a terrible idea to begin with [1].

> in addition, the wouldn't the solution then apply to "all" desktops,
> instead of "GNOME and some other" desktops?

FYI, the desktops that are covered by e.g. UDISKS_PRESENTATION_HIDE
includes desktops for which the following statements are true

 - they are using GVolumeMonitor to draw icons

 - they are shipping gvfs with the udisks (or DeviceKit-disks) volume
   monitor backend

which includes GNOME and, I think, XFCE, on most modern distros.

IMNSHO, it is rather naive to demand that "all" desktops need to
implement some feature (such as configuring what drives to ignore). It's
not like desktops share a lot of code or specs.

Good luck,
David

[1] : Hint: ignore_device only suppressed invocation of rules - the
uevent was still emitted and the device would still be part of any
enumeration either via libudev or sysfs.

<ramble>
What most people don't understand is that udev is just one tiny piece in
the *middle* of the stack... a stack where elements in the stack are
free to bypass layers - e.g. it is perfectly fine for a desktop app to
look in sysfs, thereby bypassing, say, udev and udisks.
 
So even if we still had ignore_device and things on top (like udisks ->
gvfs -> nautilus) actually respected it, it wouldn't work for the app
looking directly in sysfs (or /proc/scsi/scsi or whatever).
</ramble>.

Re: Make an un-device?

[Dan Nicholson]

On Wed, Mar 24, 2010 at 3:08 PM, David Zeuthen <david@fubar.dk> wrote:
>
> IMNSHO, it is rather naive to demand that "all" desktops need to
> implement some feature (such as configuring what drives to ignore). It's
> not like desktops share a lot of code or specs.

I think that's why he was suggesting that this be handled at the udev
level so that it _applied_ to all desktops.

--
Dan

Re: Make an un-device?

[Kay Sievers]

On Wed, Mar 24, 2010 at 23:08, David Zeuthen <david@fubar.dk> wrote:
> On Wed, 2010-03-24 at 13:52 -0400, Paul Fox wrote:
>> given how often this comes up, i think it would be very useful
>> for there to be a page fully describing the reasons that the udev
>> project thinks the feature is a bad idea.  when i asked in
>> november for the reasons behind not being able to hide devices, i
>> got somewhat vague reasons.  (and i'm clearly still not
>> convinced. :-)  simply stating "suppressing events at the udev
>> level is wrong" isn't terribly compelling.
>
> I'm sorry that you don't find this compelling but it came directly from
> both myself and the udev maintainer (Kay Sievers) - you are free to
> check the archives for better explanations. Or if you examine, in
> detail, how uevents and libudev work, you will eventually understand why
> ignore_device was a terrible idea to begin with [1].

Right, there is nothing we could "ignore" properly that way. "Hiding"
devices should probably be done by just unbinding the driver.

Kay