linux-kernel - Re: USB: on suspend to ram/disk all usb devices are replugged

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Message-Id: <20070327110524.975e7113.zaitcev@redhat.com>
Date:	Tue, 27 Mar 2007 11:05:24 -0700
From:	Pete Zaitcev <zaitcev@...hat.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Maxim Levitsky <maximlevitsky@...il.com>, gregkh@...e.de,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB development list <linux-usb-devel@...ts.sourceforge.net>,
	zaitcev@...hat.com, davidz@...hat.com
Subject: Re: USB: on suspend to ram/disk all usb devices are replugged

On Tue, 27 Mar 2007 13:15:14 -0400 (EDT), Alan Stern <stern@...land.harvard.edu> wrote:

> > Suspend to disk still causes "virtual replugging"  and I think that controller is reset and will unplug/replug devices anyway
> > Resolving this problem is very difficult. Maybe it possible to check on unplugging event that this caused by suspend  if the same device is
> > replugged then don't remove/reinstall driver, but this is very difficult to implement properly,
> > Maybe just refuse to suspend if some valuable device is connected (sorry if it is done this way already)
> 
> Long ago I posted a patch that would take care of all this.  Not just for
> UHCI, but for any USB controller.  Maybe I should dig it out, update it,
> and submit it.

Alan, BTW, look at this please:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=233697

> From David Zeuthen

> If I suspend my box, then on the resume path I see all my USB devices being
> removed and then added back. This is a problem with storage devices connected
> via USB.
.....
> The kernel not send an "remove" event if it's going to send an "add" right
> after. Instead it should enumerate the bus on resume and only send the events
> that represents how to get from the previous device tree to the current one.

> From Pete Zaitcev

> What does happen if a user suspends, unplugs a USB key, modifies its contents,
> plugs it back, and resumes? In such a case, there would be no change between
> the state of USB bus between the before-suspend state and after-resume state.

> From David Zeuthen

> In that case the user would see data corruption - just as if he mounts a piece
> of removable media in a USB card reader; yanks out the card and modifies it
> elsewhere, and then puts it back in.

> I my opinion we can't really defend ourselves against such users... We can of
> course add checks in the file system drivers in the resume hooks to validate the
> super block and mount read-only if something change. 

The GNOME hath spoken?

-- Pete
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