On Mon, Sep 17, 2012 at 04:46:08PM -0600, Kay Sievers wrote: > We are currently playing around with native btrfs multi-device support > in systemd. We already committed the needed pieces to systemd git, to > register all detected btrfs filesystems with the kernel. > > For volumes which are listed in fstab for mounting, we delay the > actual mount-attempt of a multi-device volume until we see READY > returned from BTRFS_IOC_DEVICES_READY. A line with UUID= in /etc/fstab > with "nofail" in the options field, and we can boot up without any > device plugged in. Now plugging in devices one-after-the-other until > the volume has a full tree of devices; with the last device there, > systemd just mounts the volume as expected. > > This seems to work very well so far, unless a device which is already > registered disappears, which is a kind of valid hotplug scenario we > should handle better: > > If one device of a 2-device volume is registered with the in-kernel > cache, and then the device is unplugged from the system, the cache > state does not get updated. If then the other device of the 2-device > volume is registered, BTRFS_IOC_DEVICES_READY indicates ready; but in > fact only one of two needed devices are available at that time, and > mounting fails. > > Can we somehow subscribe to device media-changes/removal to prevent > the stale device state in the in-kernel cache? > > Or alternatively make BTRFS_IOC_DEVICES_READY re-validate all involved > block devices before it returns READY?
Hrm excellent question, I'll look at what options we have in kernel to check and see if a device is still present and figure something out. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
