Comment 34 for bug 1673350

------- Comment From <email address hidden> 2017-07-11 16:24 EDT-------
Verified on 16.04 with the daily ISO (2017/07/11).

Just noticed a glitch with grub-installer and multipath,
but that's not related to this bug. I'll report a new one.

1) The dm-queue-length module is present in the installer udebs:

~ # uname -r
4.4.0-83-generic

~ # find /lib/modules/ -name dm-queue-length.ko
/lib/modules/4.4.0-83-generic/kernel/drivers/md/dm-queue-length.ko

2) And it can be used by multipath in the installer:

~ # cat <<EOF >/etc/multipath.conf
defaults {
path_selector "queue-length 0"
user_friendly_names yes
find_multipaths no
}
EOF

~ # multipath
...

~ # multipath -l
mpatha (0QEMU_QEMU_HARDDISK_drive-scsi0-0-0-0) dm-0 QEMU,QEMU HARDDISK
size=128G features='0' hwhandler='0' wp=rw
`-+- policy='queue-length 0' prio=0 status=active
`- 0:0:0:0 sda 8:0 active undef running

3) The hw-detect/disk-detect is loading the modules too.

~ # grep dm- /bin/disk-detect
<...>
log-output -t disk-detect modprobe -v -b dm-round-robin || true
log-output -t disk-detect modprobe -v -b dm-service-time || true
log-output -t disk-detect modprobe -v -b dm-queue-length || true

4) Versions used by the installer:

~ # grep multipath /var/log/syslog
<...>
Jul 11 18:52:49 anna[8788]: DEBUG: retrieving multipath-modules-4.4.0-83-generic-di 4.4.0-83.106
Jul 11 18:52:49 anna[8788]: DEBUG: retrieving multipath-udeb 0.5.0+git1.656f8865-5ubuntu2.5
<...>

~ # grep hw-detect /var/log/syslog
<...>
Jul 11 18:52:00 anna[4126]: DEBUG: retrieving hw-detect 1.117ubuntu2.2
<...>

5) initramfs is installed with the dm-queue-length module:

~ # grep dm-queue-length /target/usr/share/initramfs-tools/hooks/multipath
for x in dm-multipath dm-service-time dm-round-robin dm-queue-length; do

(initramfs) find /lib/modules -name dm-queue-length.ko
/lib/modules/4.4.0-85-generic/kernel/drivers/md/dm-queue-length.ko

6) multipath root uses the dm-queue-length module:

(initramfs) multipath -l
mpatha (0QEMU_QEMU_HARDDISK_drive-scsi0-0-0-0) dm-0 QEMU,QEMU HARDDISK
size=128G features='0' hwhandler='0' wp=rw
`-+- policy='queue-length 0' prio=0 status=active
`- 0:0:0:0 sda 8:0 active undef running

ubuntu@ubuntu:~$ mount | grep ' / '
/dev/mapper/mpatha-part2 on / type ext4 (rw,relatime,errors=remount-ro,data=ordered)

ubuntu@ubuntu:~$ sudo multipath -l mpatha
mpatha (0QEMU_QEMU_HARDDISK_drive-scsi0-0-0-0) dm-0 QEMU,QEMU HARDDISK
size=128G features='0' hwhandler='0' wp=rw
`-+- policy='queue-length 0' prio=0 status=active
`- 0:0:0:0 sda 8:0 active undef running