[systemd-devel] udevadm settle hangs due to veths in seperate network namespaces

[Daniel P. Berrange]

On Fri, Jul 12, 2013 at 02:51:10PM +0100, Daniel P. Berrange wrote:
> We're hitting a problem in libvirt where 'udevadm settle' will get stuck
> in a loop until it eventually times out. Eventually we realized this
> happens when we have any LXC containers active with veth devices in a
> separate network namespace.

Incidentally, I recall reading something by (iirc) Lennart saying that
apps really should use 'udevadm settle' at all. Libvirt uses it in a
couple of places, all related to code which obtains lists of storage
devices

 - After adding a disk partition in parted, we use it to wait for
   the /dev/sdXXNNN device nodes to all show up

 - After logging into an iscsi target with iscsiadm, we use it to
   wait for all the /dev/sdXXX devices nodes associated with the
   iSCSI target to appear.

 - After triggering a SCSI HBA rescan via sysfs, we use it to wait
   for all the /dev/sdXXX devices nodes associated with the SCI HBA
   to appear

 - After creating an NPIV virtual HBA via sysfs, we use it to wait
   for all the /dev/sdXXX devices nodes associated with the vHBA
   to appear

 - After activating an LVM volume group, we use it to wait for all
   the /dev/VGNAME/XXXX device nodes to appear

 - After deleting an LVM  volume we use it to wait for the device
   node to be removed

 - After adding an LVM  volume we use it to wait for the device
   node to be added

You can see a pattern there - after doing some action related to
storage, we need to synchronize wrt the creation/deletion of device
nodes in /dev, otherwise we miss out LUNs when we scan for the list
of device nodes associated with a HBA/VolGroup/etc. Any suggestions
for alternative techniques / approaches here ?

Daniel
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