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    SubjectRe: Flames over -- Re: Which is simpler?
    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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