Messages in this thread | | | Date | Tue, 14 Feb 2006 14:26:31 -0500 (EST) | From | Alan Stern <> | Subject | Re: Flames over -- Re: Which is simpler? |
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On Mon, 13 Feb 2006, Rafael J. Wysocki wrote:
> Hi, > > On Monday 13 February 2006 22:24, Alan Stern wrote: > > On Mon, 13 Feb 2006, Phillip Susi wrote: > }-- snip --{ > > You are complaining because you don't like the way USB was designed. > > That's fine, but it leaves you advocating a non-standardized position. > > > > Can you suggest a _reliable_ way to tell if the USB device present at a > > port after resuming is the same device as was there before suspending? > > It seems to follow from your discussion that if I have a mounted filesystem > on a USB device and I suspend to disk, I can lose data unless the filesystem > has been mounted with "sync".
That's right. It depends on your hardware, and it could be true even for suspend-to-RAM. In fact, even with "-o sync" you can lose data if your programs have information in buffers they haven't written out to disk.
If you're lucky, your hardware will support low-power modes for USB controllers while the system is asleep. Lots of hardware doesn't, however. Shutting off the power to a USB controller is equivalent to unplugging all the attached devices.
Remember that it's always a bad idea to unplug a disk drive containing a mounted filesystem. With USB that's true even when your system is asleep! The safest thing is to unmount all USB-based filesystems before suspending and remount them after resuming.
> If this is the case, there should be a big fat warning in the swsusp > documentation, but there's nothing like that in there (at lease I can't find > it easily). > > [If this is not the case, I've missed something and sorry for the noise.]
I'm not aware of any warnings about this in the documentation. If you would like to add something, please go ahead.
Alan Stern
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