From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zachary Palmer <zep_bcache-J5qI5MFTcs8@public.gmane.org>
Subject: Suspend and Hibernation Bugs
Date: Sun, 01 Sep 2013 14:10:11 -0400
Message-ID: <52238303.6040509@bahj.com>
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Hello there.  I'm not sure if this is the appropriate venue, so please 
let me know if this information should be somewhere else.  I have 
configured a Debian 7.0 installation on a Dell Inspiron 17R SE laptop to 
use a bcache root device.  The previous known working configuration for 
the laptop was:

     /dev/sda (1TB HDD)
         ...
         /dev/sda7 (used as LUKS encrypted volume)
             /dev/mapper/sda7_crypt (used as LVM PV)
                 /dev/vg0/home
                 /dev/vg0/root
                 ...
         /dev/sda8 (used as ext3 /boot)

The new configuration is

     /dev/sda (1TB HDD)
         ...
         /dev/sda7 (used as bcache backing device)
             /dev/bcache0 (used as LUKS encrypted volume)
                 /dev/mapper/bcache_crypt (used as LVM PV)
                     /dev/vg0/home
                     /dev/vg0/root
                     ...
         /dev/sda8 (used as ext3 /boot)
     /dev/sdb (32GB SSD)
         ...
         /dev/sdb3 (used as bcache caching device)

In order to get things booting, I also:

     * Installed a Linux 3.10 kernel from wheezy-backports 
(3.10-0.bpo.2-686-pae)
     * Obtained a copy of the bcache-tools source from the git repo and 
compiled it
     * Constructed a Debian package for bcache-tools using checkinstall
     * Because udev recognition wasn't enough at boot time, added a 
script /etc/initramfs-tools/scripts/init-premount/z-bcache which looks 
like this:
             #!/bin/sh -e

             # ZEP - Added (2013-08-29) because some bcache devices were 
not being detected
             #       at startup by udev.  This sloppy hack should do the 
job.

             PREREQS=""

             prereqs() { echo "$PREREQS"; }

             case "$1" in
                 prereqs)
                     prereqs
                     exit 0
                     ;;
             esac

             . /scripts/functions

             if [ -e '/sys/fs/bcache/register_quiet' ]; then
                 log_begin_msg "Scanning for bcache devices..."
                 for d in `ls /dev/sd*`; do
                     echo "$d" > /sys/fs/bcache/register_quiet 
2>/dev/null || true
                 done
                 log_end_msg "bcache device scan complete"
             else
                 log_warning_msg "/sys/fs/bcache/register_quiet not 
found; not registering devices"
             fi
     * Executed update-initramfs -u -k all to get everything working

My machine boots from /dev/sda8 and the initramfs has enough machinery 
to get the root drive mounted.  I was thrilled until I discovered that 
neither suspend nor hibernate seems to work; the suspend process seizes 
up while suspending devices and never comes back.  I booted the laptop 
from a custom Debian live disk using the same kernel 
(3.10-0.bpo.2-686-pae) and performed a series of tests:

     * When the bcache kernel module was not loaded, suspend to RAM 
worked correctly.
     * When the bcache kernel module was loaded but no devices were 
registered, suspend to RAM worked correctly.
     * When a single bcache device was registered using "echo /dev/sda7 
 > /sys/fs/bcache/register; echo /dev/sdb3 > /sys/fs/bcache/register", 
suspend to RAM failed to change the power state of the machine.
     * With a /dev/bcache0 device in use as an encrypted volume, running 
"echo freezer > /sys/power/pm_test; echo platform > /sys/power/disk; 
echo disk > /sys/power/state" allows the machine to awaken from the test 
correctly.
     * With a /dev/bcache0 device in use as an encrypted volume, running 
"echo devices > /sys/power/pm_test; echo platform > /sys/power/disk; 
echo disk > /sys/power/state" causes the machine to hang.

Has suspend/hibernate been tested with bcache?  Is it supported? I'm 
trying to figure out if it's my specific laptop hardware causing the 
issue or if bcache is somehow at fault.  (Clearly, I can get 
suspend/hibernate back if I migrate back to using just my HDD, but 
caching blocks in a fashion designed for SSDs seems like such a lovely 
idea.)

Thanks,

Zach