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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.
This rule appeared in udev v152 and it helps us to support spurious events
where we didn't have any flags set (events originated in udevadm trigger
or the watch rule). These flags are important to direct the rule application.
Now, with the help of this rule, we can regenerate old udev db content.
To implement this correctly, we need to flag all proper DM udev events with
DM_UDEV_PRIMARY_SOURCE_FLAG. That happens automatically for all ioctls
generating events originated in libdevmapper.
This prevents some confusion when libudev was not found so udev_sync was disabled
automatically. Configure was successful though giving only a tiny warning.
Also, if "dmsetup udevcreatecookie" is used, never return 0x000000 as a result if
udev is not running and keep the output blank.
We need to know whether we should wait for any uevent or not when
using udev_sync. A kernel patch was posted recently that changed the
way uevents are sent on dm device resume - it is sent only if the
device has been suspended before. There's also a new DM_UEVENT_GENERATED_FLAG
in the ioctl to notify userspace whether the event was generated.
If the uevent was not generated (e.g. the situation where the device is
*not* suspended and we call a resume), we just call dm_udev_complete
explicitly from within libdevmapper itself to prevent infinite waiting
while trying to synchronise with udev processing.
