Bug 883416

Summary:	Need a way to easily fallback to non-udev operation in libdevmapper/lvm2
Product:	Red Hat Enterprise Linux 6	Reporter:	Peter Rajnoha <prajnoha>
Component:	lvm2	Assignee:	Peter Rajnoha <prajnoha>
Status:	CLOSED ERRATA	QA Contact:	Cluster QE <mspqa-list>
Severity:	urgent	Docs Contact:
Priority:	urgent
Version:	6.4	CC:	agk, ccui, czhang, dwysocha, gbai, gholms, heinzm, jbrassow, lvm-team, lwang, msnitzer, nperic, prajnoha, prockai, qcai, thornber, tlavigne, vgoyal, zkabelac
Target Milestone:	rc	Keywords:	Regression
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:	lvm2-2.02.98-4.el6	Doc Type:	Enhancement
Doc Text:	Feature: Recognize DM_DISABLE_UDEV environment variable while using LVM2 tools, dmsetup and libdevmapper to fallback to non-udev operation fully. Setting this variable acts as a shortcut for using --noudevsync, --noudevrules and --verifyudev option in dmsetup and setting devices/obtain_device_list_from_udev=0, activation/udev_sync=0 (or --noudevsync LVM2 command line option), activation/udev_rules=0 and activation/verify_udev_operations=1 option in LVM2. Changes also apply for any libdevmapper users. Reason: Setting the DM_DISABLE_UDEV environment variable provides a more convenient way of disabling udev support in libdevmapper, dmsetup and LVM2 tools globally without a need to modify any existing configuration settings. This is mostly useful if the system environment does not use udev. Result (if any): Refer to dmsetup manual page and LVM2 manual pages as well as the comments in lvm.conf itself and descriptions of the options mentioned above.	Story Points:	---
Clone Of:	880040	Environment:
Last Closed:	2013-02-21 08:15:08 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	880040

Description Peter Rajnoha 2012-12-04 14:53:02 UTC

Add the DM_DISABLE_UDEV env var instead of setting various options directly.  The DM_DISABLE_UDEV env var gets top priority over all existing settings.

Comment 1 Peter Rajnoha 2012-12-04 14:55:29 UTC

Upstream commits:

  http://git.fedorahosted.org/cgit/lvm2.git/commit/?id=fb8cc7c63f7f5ab9e0d6d2d38f29169346a54087

  http://git.fedorahosted.org/cgit/lvm2.git/commit/?id=4891a735d343db26460f1b6218169c458d59f2a1

  http://git.fedorahosted.org/cgit/lvm2.git/commit/?id=b13d45d21d616c5512593617bbf5ed4c623805ed

  http://git.fedorahosted.org/cgit/lvm2.git/commit/?id=ed9751d9fa6638e0cae5aa38727f971eeac6516c

Comment 2 Peter Rajnoha 2012-12-04 15:22:30 UTC

To QA:

To test this, use the DM_DISABLE_UDEV=1 environment variable and then try to create/remove dm/lvm devices. This should have the same effect as setting/using:

For dmsetup:
  --noudevsync in dmsetup
  --noudevrules
  --verifyudev


For LVM2:
  devices/obtain_device_list_from_udev=0
  activation/udev_sync=0 (or --noudevsync lvm2 cmd line option)
  activation/udev_rules=0
  activation/verify_udev_operations=1


You can check that udev is bypassed by:

 - checking the /dev/mapper dir - the nodes should be created here instead of symlinks
 - /dev/<vg_name>/<lv_name> should be a symlink to /dev/mapper instead of 
/dev/dm-X
 - also checking the udev database, for example:

   udevadm info --query=all --name=/dev/mapper/vg-lvol0

P: /devices/virtual/block/dm-0
N: dm-0
S: disk/by-id/dm-name-vg-lvol0
S: disk/by-id/dm-uuid-LVM-lLYHEhwf9yDVwsA2KAIj2BGE2Tmrfa59gGQny4UDP2xCa6vl275fepLDPCG8LQLJ
E: DEVLINKS=/dev/disk/by-id/dm-name-vg-lvol0 /dev/disk/by-id/dm-uuid-LVM-lLYHEhwf9yDVwsA2KAIj2BGE2Tmrfa59gGQny4UDP2xCa6vl275fepLDPCG8LQLJ
E: DEVNAME=/dev/dm-0
E: DEVPATH=/devices/virtual/block/dm-0
E: DEVTYPE=disk
E: DM_LV_NAME=lvol0
E: DM_NAME=vg-lvol0
E: DM_SUSPENDED=0
E: DM_UDEV_DISABLE_DM_RULES_FLAG=1
E: DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG=1
E: DM_UDEV_PRIMARY_SOURCE_FLAG=1
E: DM_UDEV_RULES_VSN=2
E: DM_UUID=LVM-lLYHEhwf9yDVwsA2KAIj2BGE2Tmrfa59gGQny4UDP2xCa6vl275fepLDPCG8LQLJ
E: DM_VG_NAME=vg
E: MAJOR=253
E: MINOR=0
E: SUBSYSTEM=block

So no symlink "S:" record for /dev/mapper/vg-lvol0 and /dev/vg/lvol0. And also there are DM_UDEV_DISABLE_{DM, SUBSYSTEM}_FLAG=1 variables set.


Compared to udev records *without DM_DISABLE_UDEV*:

P: /devices/virtual/block/dm-0
N: dm-0
S: disk/by-id/dm-name-vg-lvol0
S: disk/by-id/dm-uuid-LVM-lLYHEhwf9yDVwsA2KAIj2BGE2Tmrfa59gGQny4UDP2xCa6vl275fepLDPCG8LQLJ
S: mapper/vg-lvol0
S: vg/lvol0
E: DEVLINKS=/dev/disk/by-id/dm-name-vg-lvol0 /dev/disk/by-id/dm-uuid-LVM-lLYHEhwf9yDVwsA2KAIj2BGE2Tmrfa59gGQny4UDP2xCa6vl275fepLDPCG8LQLJ /dev/mapper/vg-lvol0 /dev/vg/lvol0
E: DEVNAME=/dev/dm-0
E: DEVPATH=/devices/virtual/block/dm-0
E: DEVTYPE=disk
E: DM_LV_NAME=lvol0
E: DM_NAME=vg-lvol0
E: DM_SUSPENDED=0
E: DM_UDEV_DISABLE_LIBRARY_FALLBACK_FLAG=1
E: DM_UDEV_PRIMARY_SOURCE_FLAG=1
E: DM_UDEV_RULES_VSN=2
E: DM_UUID=LVM-lLYHEhwf9yDVwsA2KAIj2BGE2Tmrfa59gGQny4UDP2xCa6vl275fepLDPCG8LQLJ
E: DM_VG_NAME=vg
E: MAJOR=253
E: MINOR=0
E: SUBSYSTEM=block

The S:mapper/vg-lvol0 and S:vg/lvol0 is there and DM_UDEV_DISABLE_LIBRARY_FALLBACK=1 is set and no DM_UDEV_DISABLE_*_FLAG set.

Comment 3 Peter Rajnoha 2012-12-04 15:25:36 UTC

Also, if you use DM_DISABLE_UDEV=1 and at the same time udevd daemon is running, you should get these warning messages:

$ export DM_DISABLE_UDEV=1
$ lvchange -ay vg
  Udev is running and DM_DISABLE_UDEV environment variable is set. Bypassing udev, LVM will manage logical volume symlinks in device directory.
  Udev is running and DM_DISABLE_UDEV environment variable is set. Bypassing udev, LVM will obtain device list by scanning device directory.
  Udev is running and DM_DISABLE_UDEV environment variable is set. Bypassing udev, device-mapper library will manage device nodes in device directory.

Comment 4 Nenad Peric 2012-12-04 15:34:13 UTC

Adding QA ACK based on Comment #2

Comment 6 Nenad Peric 2012-12-11 15:18:07 UTC

Verified by setting DM_DISABLE_UDEV and by changing the lvm.conf
The behavior is the same, save for the lack of warnings:

  Udev is running and DM_DISABLE_UDEV environment variable is set. Bypassing udev, LVM will manage logical volume symlinks in device directory.
  Udev is running and DM_DISABLE_UDEV environment variable is set. Bypassing udev, LVM will obtain device list by scanning device directory.
  Udev is running and DM_DISABLE_UDEV environment variable is set. Bypassing udev, device-mapper library will manage device nodes in device directory.


Just a note of warning:
Even though it is possible, it is highly _not recommended_ mixing the udev and non-udev devices in a VG. 
This can cause issues later when manipulating those different LVs, especially after deleting the VG which had LVs created in such a combined way (left over orphaned/dangling nodes in /dev and /dev/mapper).

Comment 7 errata-xmlrpc 2013-02-21 08:15:08 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2013-0501.html