This patch goes some way towards fixing USB-backed persistence by
configuring the live initramfs to contain the "sd_mod" module and adding
a hacky workaround to a udev-related race condition.
For some reason, the usual udevtrigger/udevsettle pairing does not block
after we have loaded our USB modules and /dev/sda1 (for example) is ready.
Because of this, we sleep for a little while and break if a new block
device appears.
This seems to be a bug either in udev or in my understanding of how the
tool is meant to work. Some information may be gained from the casper bug:
https://bugs.launchpad.net/ubuntu/+source/casper/+bug/84591
Sleep-based hacks like this are really ugly, but I take some comfort in
finding them elsewhere in the source.
manual_add_modules sbp2
manual_add_modules sr_mod
+# Hardware: usb
+manual_add_modules sd_mod
+
# Hardware: network
auto_add_modules net
# Looking for "${root_persistence}" device or file
if [ -n "${PERSISTENT}" ] && [ -z "${NOPERSISTENT}" ]
then
+ # Load USB modules
+ num_block=$(ls -l /sys/block | wc -l)
+ for module in sd_mod uhci-hcd ehci-hcd ohci-hcd usb-storage
+ do
+ modprobe -q -b ${module}
+ done
+
+ udevtrigger
+ udevsettle
+
+ # For some reason, udevsettle does not block in this scenario,
+ # so we sleep for a little while.
+ #
+ # See https://bugs.launchpad.net/ubuntu/+source/casper/+bug/84591
+ for timeout in 5 4 3 2 1
+ do
+ sleep 1
+
+ if [ $(ls -l /sys/block | wc -l) -gt ${num_block} ]
+ then
+ break
+ fi
+ done
+
cowprobe=$(find_cow_device "${root_persistence}")
if [ -b "${cowprobe}" ]