Messages in this thread | | | Date | Thu, 5 Jan 2012 10:18:57 -0800 | From | Greg KH <> | Subject | Re: Revoking filesystems [was Re: Sysfs attributes racing with unregistration] |
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On Thu, Jan 05, 2012 at 10:13:31AM -0500, Alan Stern wrote: > On Wed, 4 Jan 2012, Eric W. Biederman wrote: > > > > Ted Ts'o has been talking about something similar but not the same -- a > > > way to revoke an entire filesystem. For example, see commit > > > 7c2e70879fc0949b4220ee61b7c4553f6976a94d (ext4: add ext4-specific > > > kludge to avoid an oops after the disk disappears). > > > > > > The use case for that is obvious and widespread: Somebody yanks out a > > > USB drive without unmounting it first. > > > > Agreed. The best I have at the moment is a library that can wrap > > filesystem methods to implement the hotplug bits. > > > > Do you know how hard it is to remove event up to the filesystem that > > sits on top of a block device? > > I don't have a clear idea of what's involved (in particular, how to go > from a block_device structure to a mounted filesystem). But the place > to do it would probably be block/genhd.c:invalidate_partition(). Ted > can tell you if there's a better alternative. > > > Do you know how hard it is to detect at mount time if a block device > > might be hot-plugable? We can always use a mount option here and > > make userspace figure it out, but being to have a good default would > > be nice. > > I don't think it's possible to tell if a device is hot-unpluggable. > For example, the device itself might not be removable from its parent, > but the parent might be hot-unpluggable. You'll probably have to > assume that every device can potentially be unplugged, one way or > another.
These days, _any_ block device is hot unplugable, what with PCI hotplug and the like (running in a virtual machine, etc.) So you always need to assume that any device can go away at any point in time.
thanks,
greg k-h
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