[PATCH] nvme_fc auto-connect scripts

[Hannes Reinecke]

On 10/09/2017 10:10 PM, James Smart wrote:
> Sagi recently posted a "one-shot" call to nvme-connect via a systemd
> script. FC has no problems operating with it assuming all the required
> connect fields are present (host_traddr required).
> 
> However FC is a bit more dynamic, and we've built up scripts that can
> be triggered whenever a new FC remote port with a discovery subsytem is
> detected. Whenever such a port is detected (by registration of the
> remoteport with the nvme_fc transport by the lldd), the transport
> generates a udev event.  A udev rule is created that parses the event
> information into the FC remote port (traddr) that supports a discovery
> subsystem and the FC host port that is connected to the FC remote port
> (host_traddr). The rule then invokes an instance-based systemd service
> to perform a "nvme connect-all" with the traddr and host-traddr info.
> 
> To resolve some issues seen by discovery of remote ports before the udev
> service was running and where the events were not replayed, there is an
> additional systemd service that runs once and invokes a script which
> locates the FC host ports on the system, looks for any connected FC
> remote ports with discovery subsystems, and invokes a connect-all for
> them.  The FC port information is specific to lpfc attributes currently,
> but when the shared transport is in place, they will be common.
> 
> I don't claim to be a systemd expert, so comments are certainly welcome.
> 
In general I'm not in favour of calling 'systemctl start' from a udev
rule; this typically will cause systemd to rearrange the internal
dependency chain, and might trigger various services to be enabled or
disabled.

The 'normal' flow of events is:

kernel device -> uevent -> udev rules -> systemd services

ie for the autoconnect it would be _far_ better if we could have an
event per NVMe lport device, as then we could call 'connect' on the
lport device.

So a better workflow would be to have the 'discovery' event trigger a
'change' (or 'add'?) event on the lports, and then we could have
per-lport udev rules triggering the actualy connect.

Let's see if I can come up with something along these lines.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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