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We can't rely on the fact that udev should prepare the node with right major
and minor number to trigger the module autoloading. We have to take into
account that the node could be missing or it could exist with improper
major and minor number assigned (e.g. from previous kernel versions in
an environment with static nodes and without udev). Make any corrections
if needed!
This can happen with older rules (without support for synthesized events)
that are still part of initrd while using new udev rules in the system itself.
The consequence was that new udev rules incorrectly assumed that not having
DM_UDEV_PRIMARY_SOURCE_FLAG set always means the uevent is synthesized and
inappropriate (device is still not properly activated) and so it should be
ignored. However, initrd is not updated automatically while updating the
libdevmapper/udev rules in the system and so we end up with the rules not
detecting and setting crucial parts in the initrd environment and the rules
in the system that rely on the information that should have been stored in
udev db (which is incorrect in this configuration, of course).
The overall consequence is that the update of libdevmapper/lvm2 without
regenerating the initrd could end up with a boot failure! Ignoring the event
means removing any existing symlinks in /dev!
To fix this, increase udev rules version to make a difference. So from now on,
mark rules without proper support for synthesized events as
DM_UDEV_RULES_VSN="1" and 2 (or higher) if that support is included.
We still need to detect this one! We're not so strict with CHANGE events as
with the ADD events while applying filters in the rules so this one would
pass and it would process the rules prematurely (because it appears *before*
the actual CHANGE event used when resuming a DM device while setting read-only
state at the same time).
udev_sync feature requires semaphores (part of System V IPC) to be configured
in kernel (CONFIG_SYSVIPC). Check whether it is supported and if not, give
a warning message and disable udev synchronisation code automatically to
avoid any further error states and associated problems.
One should use the kernel with System V IPC support enabled or libdevmapper
with udev_sync feature disabled.
Switch dmeventd to use dm_create_lockfile and drop duplicate code.
Allow clvmd pidfile to be configurable.
Switch cmirrord and clvmd to use dm_create_lockfile.
For now, this is just a precaution. Normally, all the other (non-dm) rules
should check DM_UDEV_DISABLE_OTHER_RULES_FLAG and therefore avoid setting
any inotify watches as well. But let's make sure.
Support for final assignment of the "nowatch" rule (the use of ":=") will
appear in next udev release, v160. This should also work in previous udev
versions but the setting won't be sealed so any further OPTIONS="watch" will
always prevail there.
We may want to add more specific "nowatch" rules later if needed.
We can use DM_UDEV_PRIMARY_SOURCE_FLAG to identify the spurious events
and use it as an indication that the device has already been activated before
(and hence we can find this property in udev database).
WARNING: This change requires udev startup script to preserve udev database
from initrd. All the information stored there during activation of devices
is important for the initial "udevadm trigger --action=add" call that is
used in udev startup script. If not done this way, udev startup script needs
to define DM_UDEV_PRIMARY_SOURCE_FLAG=1 property for any ADD events it uses.
A kernel patch is on its way for 2.6.35 adding support for dm-mod module
autoload. Udev v155 and higher is able to read static node information given
in modules.devname (extracted by depmod before) and will create such nodes
at its start. The first access to such node will load the module automatically
(directly in kernel) before the actual read/write operation is processed.
