ON-15146: Enable ZF_ATTR shrub_controller_id for enabling tcpdirect stacks to work with a given shrub_controller

[krishd-amd]

TESTING DONE:
On machine 1)
sudo shrub_controller -c 37 -d
In a new terminal
ZF_ATTR="interface=enp1s0f0;shrub_controller_id=37" ./build/gnu_x86_64/bin/zf_apps/static/zfsink 224.0.2.23:8080

With the above, i see the interfaces negotiate with the shrub_controller
ci Info: shrub_controller created a new server on interface with ifindex 3 buffer_count 4 hwport 5

zf_stackdump dump also shows shrub_controller_id

[krishd@dellr230t tcpdirect]$ sudo ./build/gnu_x86_64/bin/zf_stackdump dump
============================================================
onload version=547533a0d5 2025-09-08 master
tcpdirect version=9.1.0 23d32e4 2025-09-10 ON-15146
name=enp1s0f0/003 interface=enp1s0f0 vlan_id=65535
  pool: pkt_bufs_n=18048 free=18048
  config: tcp_timewait_ticks=666 tcp_finwait_ticks=666 ctpio_threshold=65535
  config: tcp_initial_cwnd=0 ms_per_tcp_tick=90
  alts: n_alts=0
  stats: ring_refill_nomem=0 cplane_alien_ifindex=0
         tcp_retransmits=0
  discards: discard_csum_bad=0 discard_mcast_mismatch=0
         discard_crc_bad=0 discard_trunc=0 discard_rights=0
         discard_ev_error=0 discard_other=0 discard_inner_csum_bad=0
         non_tcpudp=0
]
nic0: vi=3 vi_flags=3000000 nic_flags=1 intf=enp1s0f0 index=3 hw=5A0
  txq: pio_buf_size=0 added=0 removed=0
============================================================
UDP RX enp1s0f0/003:0
  filter: lcl=224.0.2.23:8080 rmt=0.0.0.0:0
  rx: unread=0 begin=0 process=0 end=0
  udp rx: release_n=0 q_drops=0
------------------------------------------------------------
---------------------attributes-------------------------------
tx_ring_max=512
rx_ring_max=512
tx_timestamping=0
rx_timestamping=0
ctpio=1
ctpio_mode=sf-np
rx_datapath=express
phys_address_mode=0
shrub_controller_id=37

If a user attempts to set the shrub_controller as -2, or 100000
[krishd@dellr230t tcpdirect]$ ZF_ATTR="interface=enp1s0f0;shrub_controller_id=10000" ./build/bin/zf_apps/static/zfsink 224.0.2.23:808
0
1000 | Bad shrub_controller_id; value must be -1 or in range 0 to 9999
ERROR: main: ZF_TRY(zf_stack_alloc(attr, &stack)) failed
ERROR: at src/tests/zf_apps//zfsink.c:265
ERROR: rc=-22 (Invalid argument) errno=0

If a user attempts to connect to a controller that is not running.
[krishd@dellr230t tcpdirect]$ ZF_ATTR="interface=enp1s0f0;shrub_controller_id=38" ./build/bin/zf_apps/static/zfsink 224.0.2.23:8080
1000 | Failed to allocate VI (rc = -2)
ERROR: main: ZF_TRY(zf_stack_alloc(attr, &stack)) failed
ERROR: at src/tests/zf_apps//zfsink.c:265
ERROR: rc=-2 (No such file or directory) errno=2
Aborted (core dumped)

[krishd-amd]

Would you prefer I adjust the ef_alloc_vi_from_pd to functions to take the shrub_controller parameter here? This just seems like an easier solution with fewer wider changes.

[jfeather-amd]

I'm not too sure how I feel about setenv here. It does indeed feel like it's probably the easiest way to get this done, but equally some kind of ef_vi_set_shrub_controller function might feel more pragmatic. I'm not too familiar with the structure of shrub though, so if such an approach is too cumbersome it might be a good idea to stick with setenv for now.

[jfeather-amd]

Looks reasonable, mainly just a few notes on avoiding magic numbers.

[jfeather-amd]

Not sure if appropriate to add here, but I think it would be nice to have a macro (or otherwise) for the "no shrub" value, e.g.:

#define ZF_SHRUB_CONTROLLER_ID_NO_SHRUB -1

[jfeather-amd]

I'm not too sure how I feel about setenv here. It does indeed feel like it's probably the easiest way to get this done, but equally some kind of ef_vi_set_shrub_controller function might feel more pragmatic. I'm not too familiar with the structure of shrub though, so if such an approach is too cumbersome it might be a good idea to stick with setenv for now.