casper-helpers:where_is_mounted fails in obscure cases

Binary package hint: casper

where_is_mounted() in casper-helpers contains the following line:

grep "^$device " /proc/mounts | read d mountpoint rest

This will not work, as the read command is executed in a subshell because of the pipeline and so does not set the variables in the main script. The following should work instead:

mountpoint=`grep "^$device " /proc/mounts | awk '{print $2}'`

(tested at the commandline from an interrupted initramfs)

This will only cause problems if casper is looking for files to mount persistently on an already-mounted device, and that device is not mounted on whatever directory was left in $mountpoint from its previous use. The situation I encountered it in was trying to loopback mount an ext3 casper-rw file which was on the same partition as an iso image I was using with "iso-scan/filename=xxx."

This might explain bug #258990.

(OT: is there a reason to restrict find_cow_device to only looking for loopback-mountable images on vfat filesystems?)