[PATCH v3] nvme-tcp: Print actual source IP address through sysfs "address" attr

[Belanger, Martin]

> > From: Martin Belanger <martin.belanger at dell.com>
> >
> > TCP transport relies on the routing table to determine which source
> > address and interface to use when making a connection. Currently,
> > there is no way to tell from userspace where a connection was made.
> > This patch exposes the actual source address using a new field named
> > "src_addr=" in the "address" attribute.
> >
> > This is needed to diagnose and identify connectivity issues. With the
> > source address we can infer the interface associated with each
> > connection.
> >
> > This was tested with nvme-cli 2.0 to verify it does not have any
> > adverse effect. The new "src_addr=" field will simply be displayed in
> > the output of the "list-subsys" or "list -v" commands as shown here.
> >
> > $ nvme list-subsys
> > nvme-subsys0 - NQN=nqn.2014-08.org.nvmexpress.discovery
> > \
> >   +- nvme0 tcp
> > traddr=192.168.56.1,trsvcid=8009,src_addr=192.168.56.101 live
> 
> I wonder how this works with udev events etc for auto-connect? and also for
> uniqueness checks...

Udev events are triggered by device properties (which are not the same as attributes).
The properties are found in the attribute "uevent". For example:

$ cat /sys/class/nvme/nvme1/uevent
MAJOR=238
MINOR=1
DEVNAME=nvme1
NVME_TRTYPE=tcp
NVME_TRADDR=::ffff:192.168.56.1
NVME_TRSVCID=8009
NVME_HOST_TRADDR=none
NVME_HOST_IFACE=enp0s8

The change I'm proposing does not affect device properties and therefore no impact on udev rules.

With regards to uniqueness checks, there is only one place in libnvme where we read and check the "address" attribute (file: tree.c, function: nvme_ctrl_alloc). The code will simply skip "src_address=" and extract all the other known keys from "address".

Martin