`inet:setopts/2` return 'ok' for `add_membership` and `multicast_if` even if `IfAddress` is not avail

[miaxon]

Describe the bug
inet:setpopts/2 return ok when {error, Error} expected.

To Reproduce
In erlang shell try set multicat_if option with unavail address:

1> {ok, S} = gen_udp:open(0).
{ok,#Port<0.4>}
2> inet:setopts(S, [{multicast_if, {1,2,3,4}}]).
ok

Expected behavior
Expected return {error, eaddrnotavail}

Affected versions
26.1.2

Additional context
Debug output:

1> {ok, S} = gen_udp:open(0).
INET-DRV-DBG[10723][-1,<0.86.0>] inet_ctl -> SETOPTS
INET-DRV-DBG[13970][<0.86.0>] packet_inet_ctl -> OPEN
INET-DRV-DBG[10723][19,<0.86.0>] inet_ctl -> SETOPTS
INET-DRV-DBG[6795][19,<0.86.0>] inet_set_opts -> opt: 7
INET-DRV-DBG[7177][19,<0.86.0>] inet_set_opts(rcvbuf) -> 8192
INET-DRV-DBG[7673][19,<0.86.0>] inet_set_opts -> try set opt (1) 8
inet_setopt -> try trick setopt with
   fd:        19
   proto:     1
   type:      8
   sz:        4
   propagate: 0
INET-DRV-DBG[7680][19,<0.86.0>] inet_set_opts -> set opt result: 0
INET-DRV-DBG[6795][19,<0.86.0>] inet_set_opts -> opt: 22
INET-DRV-DBG[6839][19,<0.86.0>] inet_set_opts(active) -> active (ival): active (1)
(drivers/common/inet_drv.c / 7718) sock_select(0x000055f2fe967f60): flags=01, onoff=1, event_mask=01
INET-DRV-DBG[11023][19,<0.86.0>] inet_ctl -> BIND
{ok,#Port<0.4>}

2> inet:setopts(S, [{multicast_if, {1,2,3,4}}]).
INET-DRV-DBG[10723][19,<0.86.0>] inet_ctl -> SETOPTS
INET-DRV-DBG[6795][19,<0.86.0>] inet_set_opts -> opt: 11
INET-DRV-DBG[7376][19,<0.86.0>] inet_set_opts(multicast-if) -> 16909060 (67305985)
inet_set_opts(0x000055f2fe967f60): s=19, IP_MULTICAST_IF = 1020304
INET-DRV-DBG[7673][19,<0.86.0>] inet_set_opts -> try set opt (0) 32
inet_setopt -> try trick setopt with
   fd:        19
   proto:     0
   type:      32
   sz:        4
   propagate: 0
INET-DRV-DBG[7680][19,<0.86.0>] inet_set_opts -> set opt result: -1
ok

inet_set_opts return -1, but inet:setopts/2 return ok.

strace :

[pid 58502] getsockopt(19, SOL_SOCKET, SO_PRIORITY, [0], [4]) = 0
[pid 58502] getsockopt(19, SOL_IP, IP_TOS, [0], [4]) = 0
[pid 58502] setsockopt(19, SOL_SOCKET, SO_RCVBUF, [8192], 4) = 0
[pid 58502] setsockopt(19, SOL_IP, IP_TOS, [0], 4) = 0
[pid 58502] setsockopt(19, SOL_SOCKET, SO_PRIORITY, [0], 4) = 0
[pid 58502] bind(19, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
[pid 58502] getsockname(19, {sa_family=AF_INET, sin_port=htons(42147), sin_addr=inet_addr("0.0.0.0")}, [112 => 16]) = 0
[pid 58502] getsockopt(19, SOL_SOCKET, SO_PRIORITY, [0], [4]) = 0
[pid 58502] getsockopt(19, SOL_IP, IP_TOS, [0], [4]) = 0
[pid 58502] setsockopt(19, SOL_IP, IP_MULTICAST_IF, [67305985], 4) = -1 EADDRNOTAVAIL (Cannot assign requested address)

[miaxon]

Looks like propagate variable must be set to 1 (true) for multicat_if. Or not?

https://github.com/erlang/otp/blob/master/erts/emulator/drivers/common/inet_drv.c#L6764

I'm not sure I understand this comment correctly:

/* Set to 1 if failure to set this option
should be propagated to erlang (not all
errors can be propagated for BC reasons) */

What is BC in this context?

[miaxon]

Similar behavior is also implemented for the option add_membership

2> gen_udp:open(0, [{add_membership,{{232,252,0,100},{1,2,3,4}}}]).
{ok,#Port<0.5>}

[pid 14876] socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP) = 20
[pid 14876] getsockopt(20, SOL_SOCKET, SO_PRIORITY, [0], [4]) = 0
[pid 14876] getsockopt(20, SOL_IP, IP_TOS, [0], [4]) = 0
[pid 14876] setsockopt(20, SOL_IP, IP_ADD_MEMBERSHIP, {imr_multiaddr=inet_addr("232.252.0.100"), imr_interface=inet_addr("1.2.3.4")}, 12) = -1 ENODEV (No such device)
[pid 14876] getsockopt(20, SOL_SOCKET, SO_PRIORITY, [0], [4]) = 0
[pid 14876] getsockopt(20, SOL_IP, IP_TOS, [0], [4]) = 0
[pid 14876] setsockopt(20, SOL_SOCKET, SO_RCVBUF, [8192], 4) = 0
[pid 14876] setsockopt(20, SOL_IP, IP_TOS, [0], 4) = 0
[pid 14876] setsockopt(20, SOL_SOCKET, SO_PRIORITY, [0], 4) = 0
[pid 14876] bind(20, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
[pid 14876] getsockname(20, {sa_family=AF_INET, sin_port=htons(36052), sin_addr=inet_addr("0.0.0.0")}, [112 => 16]) = 0

Still looks like a bug.

propagate must be 1 for add_membersip and multicast_if

[bmk]

If you do the same with 'socket' it works as expected.
I will look into it.

[bmk]

Also do not know what BC stands for. Unless it was supposed to be PC (Politically Correct).

[bmk]

Raimo knew: BC = Backwards Compatibility

[bmk]

Also:
`8> {ok, S2} = gen_udp:open(0, [{inet_backend, socket}]).
{ok,{'$inet',gen_udp_socket,
{<0.95.0>,
{'$socket',#Ref<0.2221571745.2128216065.255332>}}}}

9> inet:setopts(S2, [{multicast_if, {1,2,3,4}}]).
{error,eaddrnotavail}
`

[miaxon]

Thank you for answer. I see this is not a bug.