Merge ~mwhudson/casper:lp-1926137-focal into casper:focal

[Michael Hudson-Doyle]

only use a partition from the blockdev holding the livefs for auto logs

https://bugs.launchpad.net/ubuntu/+source/casper/+bug/1926137 describes
a situation where a partition called "writable" on the disk the user
wanted to install to was mounted and then caused the install to fail.
To avoid this, change things to only write logs to a partition on the
same block device as that holding the livefs by default.

This is a backport from tip. It fixes a bug that doesn't have a simple workaround but it does change behaviour: previously if you'd burnt the installer to an ISO and created a USB stick with a filesystem with label 'writable', logs would have been written to the USB stick. With this branch, they won't. But that doesn't seem like a particularly common case (it's certainly not the default case this code is intended to cover).

Unmerged commits

b588f36... by Michael Hudson-Doyle on 2021-07-19

only use a partition from the blockdev holding the livefs for auto logs

https://bugs.launchpad.net/ubuntu/+source/casper/+bug/1926137 describes
a situation where a partition called "writable" on the disk the user
wanted to install to was mounted and then caused the install to fail.
To avoid this, change things to only write logs to a partition on the
same block device as that holding the livefs by default.

diff --git a/debian/changelog b/debian/changelog
index d995221..746a3e8 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+casper (1.445.2) UNRELEASED; urgency=medium
+
+  * Only use a partition from the blockdev holding the livefs for auto logs.
+    (LP: #1926137)
+
+ -- Michael Hudson-Doyle <[e-mail]>  Mon, 19 Jul 2021 12:39:36 +1200
+
 casper (1.445.1) focal; urgency=medium
 
   * casper SRU for point release LP: #1884933:
diff --git a/scripts/casper b/scripts/casper
index f1d09ee..b7d74e4 100644
--- a/scripts/casper
+++ b/scripts/casper
@@ -843,6 +843,59 @@ find_livefs() {
     return 1
 }
 
+setup_auto_log_persistence() {
+    # If there is a writable (or casper-rw) filesystem on a partition
+    # of the same block device we found the live filesystem on and
+    # we're not already using it for persistence, use it for logs and
+    # crash reports.
+    #
+    # The goal here is to do this in the common case where the image
+    # has been dd-ed onto a USB stick that has some extra space that
+    # can be used for logs. Any kind of deviation from this scenario
+    # and we just abort to avoid situations like
+    # https://bugs.launchpad.net/ubuntu/+source/casper/+bug/1926137
+    # where a partition called "writable" on the disk the user wanted
+    # to install to was mounted and then caused the install to fail.
+    if [ -n "$PERSISTENT" ] || [ -n "$NOPERSISTENT" ]; then
+        return
+    fi
+    if [ ! -e "/dev/disk/by-label/$(root_persistence_label)" ]; then
+        return
+    fi
+    livefs_src_dev=$(what_is_mounted $mountpoint)
+    if [ -z "$livefs_src_dev" ]; then
+        return
+    fi
+    livefs_src_sysfs=$(readlink -f "/sys/class/block/$(basename $livefs_src_dev)")
+    if [ ! -f $livefs_src_sysfs/partition ]; then
+        return
+    fi
+    livefs_dev=$(cat $livefs_src_sysfs/../dev)
+    pers_dev=$(readlink -f "/dev/disk/by-label/$(root_persistence_label)")
+    pers_sysfs=$(readlink -f "/sys/class/block/$(basename $pers_dev)")
+    if [ ! -f $pers_sysfs/partition ]; then
+        return
+    fi
+    pers_dev=$(cat $pers_sysfs/../dev)
+    if [ $livefs_dev != $pers_dev ]; then
+        return
+    fi
+    mkdir /log-persistence
+    if mount -w "/dev/disk/by-label/$(root_persistence_label)" /log-persistence; then
+        local i=0 d=$(date -uIdate) pdir
+        while :; do
+            pdir=/log-persistence/install-logs-$d.$i
+            if [ ! -e $pdir ]; then
+                mkdir -p $pdir/log $pdir/crash
+                mount --bind $pdir/log "${rootmnt}/var/log"
+                mount --bind $pdir/crash "${rootmnt}/var/crash"
+                break
+            fi
+            i=$((i+1))
+        done
+    fi
+}
+
 mountroot() {
     exec 6>&1
     exec 7>&2
@@ -923,24 +976,7 @@ mountroot() {
 
     mount_images_in_directory "${livefs_root}" "${rootmnt}"
 
-    if [ -z "$PERSISTENT" ] && [ -z "$NOPERSISTENT" ] && [ -e "/dev/disk/by-label/$(root_persistence_label)" ]; then
-        # If there is a casper-rw filesystem and we're not using it
-        # for persistence, use it for logs and crash reports.
-        mkdir /log-persistence
-        if mount -w "/dev/disk/by-label/$(root_persistence_label)" /log-persistence; then
-            local i=0 d=$(date -uIdate) pdir
-            while :; do
-                pdir=/log-persistence/install-logs-$d.$i
-                if [ ! -e $pdir ]; then
-                    mkdir -p $pdir/log $pdir/crash
-                    mount --bind $pdir/log "${rootmnt}/var/log"
-                    mount --bind $pdir/crash "${rootmnt}/var/crash"
-                    break
-                fi
-                i=$((i+1))
-            done
-        fi
-    fi
+    setup_auto_log_persistence
 
     # initialize the /var/crash directory in overlayfs so that inotify for
     # /var/crash works and update-notifier will notify of crashes
diff --git a/scripts/casper-helpers b/scripts/casper-helpers
index 7479d98..01e419f 100644
--- a/scripts/casper-helpers
+++ b/scripts/casper-helpers
@@ -65,6 +65,10 @@ where_is_mounted() {
     return 1
 }
 
+what_is_mounted() {
+    cat /proc/mounts | awk -v P=$1 '$2 == P { print $1 }'
+}
+
 lastline() {
     while read lines ; do
         line=${lines}