Bug 954041

Description of problem:
Switching from non-multipathed /boot to multipathed boot is simple,  You simply need to enable multipathing on the /boot device, and rerun dracut, adding the multipath module.

However, if you remake the initramfs while you have multipathed /boot, switching back fails in the initramfs.

This is because when dracut makes an initramfs with non-multipathed boot it has the following scripts:

# cat usr/lib/dracut/hooks/emergency/80-\\x2fdev\\x2fdisk\\x2fby-uuid\\x2f5c9be980-d811-41e2-aac5-c4a5cbd8ff09.sh 
[ -e "/dev/disk/by-uuid/5c9be980-d811-41e2-aac5-c4a5cbd8ff09" ] || warn ""/dev/disk/by-uuid/5c9be980-d811-41e2-aac5-c4a5cbd8ff09" does not exist"

# cat usr/lib/dracut/hooks/initqueue/finished/devexists-\\x2fdev\\x2fdisk\\x2fby-uuid\\x2f5c9be980-d811-41e2-aac5-c4a5cbd8ff09.sh 
[ -e "/dev/disk/by-uuid/5c9be980-d811-41e2-aac5-c4a5cbd8ff09" ]

which checks for the /boot device by uuid, and works with either multipath or non-multipathed devices.

When dracut makes an initramfs with multipathed /boot it has the following scripts:

# cat usr/lib/dracut/hooks/emergency/80-\\x2fdev\\x2fmapper\\x2fmpathgp1.sh 
[ -e "/dev/mapper/mpathgp1" ] || warn ""/dev/mapper/mpathgp1" does not exist"

# cat usr/lib/dracut/hooks/initqueue/finished/devexists-\\x2fdev\\x2fmapper\\x2fmpathgp1.sh 
[ -e "/dev/mapper/mpathgp1" ]

which explicitly checks for a multipath device.

Version-Release number of selected component (if applicable):

dracut-027-36.git20130418.fc20.x86_64

How reproducible:
Always

Steps to Reproduce:
These steps will reproduce the problem without actually needing multiple paths to your /boot device

1. install multipath

# yum install device-mapper-multipath

2. setup multipath with a default config

# mpathconf --enable

3. Get the UID for the device with your boot partition

# udevadm info --export-db | less

you want ID_SERIAL from the scsi device that includes your boot partition
(so /dev/sda if your boot partition is on /dev/sda1)

4. Force multipath to set up a multipath device on your boot device, even
though it only has a single device.

# echo /<ID_SERIAL>/ >> /etc/multipath/wwids

for example

# echo /WDC_WD800JD-75MSA3_WD-WMAM9FU71040/ >> /etc/multipath/wwids

5. backup a copy of your current initramfs, so you can boot into it later

6. Remake you initramfs with multipathing

# dracut -H --add "multipath" -f <initramfs> <version>

7. Reboot

Your machine should come up with multipathed /boot (and root if they are on the
same device)

8. (optional, remake the intramfs again, reboot, and verify that you can boot
just fine with this initramfs.  It will now be specifically looking for
your multipath device)

9. Disable multipathing on /boot

delete the

/<ID_SERIAL>/

line for your boot device from /etc/multipath/wwids

10. remake you initramfs again

This initramfs will not start up multipath on your /boot device.  However it will explicitly look for that multipath device on bootup

11. reboot

Actual results:
Boot fails in the initramfs

dracut-initqueue[182]: Warning: Could not boot.
dracut-initqueue[182]: Warning: /dev/mapper/mpathgp1 does not exist
         Starting Dracut Emergency Shell...
Warning: /dev/mapper/mpathgp1 does not exist


Expected results:
Your machine boots up without multipathed /boot

Additional info:
If I manually unpack the broken initramfs, replace the multipath specific files with the /dev/disk/by-uuid versions of the files in usr/lib/dracut/hooks/emergency and usr/lib/dracut/hooks/initqueue/finished, and then reassemble the initramfs and reboot, everything works fine.