[dm-devel] [PATCH] multipathd: handle fpin events

[Muneendra Kumar M]

Hi  Martin,
Apologies for the delayed response .

>Interesting idea. Are you aware of a technology for non-FC transports
that could take the role of FPIN? I have to admit I'm not, but that
doesn't mean they don't exist or won't exist in the future.
....
...
>If we want to modularize this, we need a *generic* event listener thread.
A module would basically provide an fd for that thread to poll on, and a
callback to be called when an event occurs. This idea appeals to me a lot,
in particular because we already have an event listener (the uevent
listener thread) >which is sitting idle most of the time.
>So Muneendra, instead of creating a new receiver thread, you would extend
the existing uevent listener to handle the FPIN events as well.
>The thread would now add uevents to the uevent list and FPIN events to
the FPIN events list.

[Muneendra] Could you please refer to my query below
....
....
....

>One word of caution here: we must be careful not to over-engineer.
>As long as no other mechanism like FPIN for other transports is
conceivable, generalizing the concept makes only so much sense.
>Therefore we shouldn't hold back the FPIN patches until we have conceived
of a generic mechanism, which may take a lot of time to develop. If
another mechanism becomes available, we could still try to generalize the
concept, if we keep the current additions clean and well-separated from
the core >multipathd code.

>However I am really thrilled by the prospect of generalizing event
handling and reusing the uevent threads for FPIN. That would reduce
complexity a lot, which is a good thing IMO.

I have a query with respect to generalizing event handling and reusing the
uevent threads  .
Please correct me if iam wrong.

FPIN events work on NETLINK_SCSITRANSPORT
	netlink_kernel_create(&init_net, NETLINK_SCSITRANSPORT,  &cfg);
==>scsi_netlink.c

whereas uvents  works on NETLINK_KOBJECT_UEVENT.
	   netlink_kernel_create(net, NETLINK_KOBJECT_UEVENT, &cfg);
==>kobject_uevent.c


I am not sure whether we can reuse the uevent threads for both uevents and
fpin events.
In case if my understanding is wrong could you please clarify on the same.

Best
Martin

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