With the Fibre Channel NPIV (N_Port ID Virtualization) feature,
a single physical N_Port (e.g., PCI address) can have multiple
N_Port IDs (e.g., different fc_host nodes) - which can connect
to the same target LUN (e.g., fc_remote_port's port_name and
LUN number).

Thus, in order to be unique, the device persistent path should
include the fc_vport's port_name (only if the fc_vport is used),
in addition to the already in use PCI address, fc_remote_port's
port_name and LUN number.

The patch merges the 2 proposals submitted upstream, addressing
some problems with both:
- #2500 (don't replace the fc_rport's port_name with fc_vport's)
- #2665 (don't add a fc_host/fc_vport's port_name if not needed)

Links
- #2500
- #2665

Built, checked, tested on RHEL Server 7.1 with no regressions.

With the patch, /dev/disk/by-path symlinks are created correctly,
and are unique, backward-compatible with the physical port case:
- physical port (no vport field)
- virtual ports (w/ vport field)

    # ls -l /dev/disk/by-path | grep 0001:09:00.0
    <...> pci-0001:09:00.0-fc-0x500507680b2255fe-lun-0 -> ../../sdh
    <...> pci-0001:09:00.0-fc-0x500507680b2255ff-lun-0 -> ../../sdi
    <...> pci-0001:09:00.0-vport-0x5001a4aaf00a6785-fc-0x500507680b2255fe-lun-0 -> ../../sde
    <...> pci-0001:09:00.0-vport-0x5001a4aaf00a6785-fc-0x500507680b2255ff-lun-0 -> ../../sdd
    <...> pci-0001:09:00.0-vport-0x5001a4ad99d8c2de-fc-0x500507680b2255fe-lun-0 -> ../../sdc
    <...> pci-0001:09:00.0-vport-0x5001a4ad99d8c2de-fc-0x500507680b2255ff-lun-0 -> ../../sdb

Accordingly w/ sysfs:

    # ls -ld /sys/block/sd* | grep host1
    <...> /sys/block/sdb -> ../devices/pci0001:00/<...>/0001:09:00.0/host1/vport-1:0-0/host3/rport-3:0-1/target3:0:0/3:0:0:0/block/sdb
    <...> /sys/block/sdc -> ../devices/pci0001:00/<...>/0001:09:00.0/host1/vport-1:0-0/host3/rport-3:0-2/target3:0:1/3:0:1:0/block/sdc
    <...> /sys/block/sdd -> ../devices/pci0001:00/<...>/0001:09:00.0/host1/vport-1:0-2/host5/rport-5:0-1/target5:0:0/5:0:0:0/block/sdd
    <...> /sys/block/sde -> ../devices/pci0001:00/<...>/0001:09:00.0/host1/vport-1:0-2/host5/rport-5:0-2/target5:0:1/5:0:1:0/block/sde
    <...> /sys/block/sdh -> ../devices/pci0001:00/<...>/0001:09:00.0/host1/rport-1:0-3/target1:0:0/1:0:0:0/block/sdh
    <...> /sys/block/sdi -> ../devices/pci0001:00/<...>/0001:09:00.0/host1/rport-1:0-4/target1:0:1/1:0:1:0/block/sdi

The symlinks still include the fc_remote_port's (target) port_name:

    # grep . /sys/class/fc_remote_ports/rport-{3:0-{1,2},5:0-{1,2},1:0-{3,4}}/port_name
    /sys/class/fc_remote_ports/rport-3:0-1/port_name:0x500507680b2255ff
    /sys/class/fc_remote_ports/rport-3:0-2/port_name:0x500507680b2255fe
    /sys/class/fc_remote_ports/rport-5:0-1/port_name:0x500507680b2255ff
    /sys/class/fc_remote_ports/rport-5:0-2/port_name:0x500507680b2255fe
    /sys/class/fc_remote_ports/rport-1:0-3/port_name:0x500507680b2255fe
    /sys/class/fc_remote_ports/rport-1:0-4/port_name:0x500507680b2255ff

And now include the fc_vport's (virtual host) port_name *if* it's from a fc_vport:

    # grep . /sys/class/fc_host/host1/port_name /sys/class/fc_vports/vport-1:0-{0,2}/port_name
    /sys/class/fc_host/host1/port_name:0x10000090fa8f0ebc
    /sys/class/fc_vports/vport-1:0-0/port_name:0x5001a4ad99d8c2de
    /sys/class/fc_vports/vport-1:0-2/port_name:0x5001a4aaf00a6785

Signed-off-by: Mauricio Faria de Oliveira <[email protected]>
Reported-by: Srikanth B. Aithal <[email protected]>