From the smb.conf man page:

---
In order to support SMB3 multi-channel configurations, smbd understands some extra data that can be appended after the actual interface with this extended syntax:

interface[;key1=value1[,key2=value2[...]]]

Known keys are speed, capability, and if_index. Speed is specified in bits per second. Known capabilities are RSS and RDMA. The if_index should be used with care: the values must not coincide with indexes used by the kernel. Note that these options are mainly intended for testing and development rather than for production use. At least on Linux systems, these values should be auto-detected, but the settings can serve as last a resort when autodetection is not working or is not available.
---

This feature is currently broken. The interfaces line is parsed as type P_CMDLIST. This type treats comma, semicolon, and whitespace as token delimiters. A line like this:

interfaces = eth0;capability=RSS,speed=10000000000

effectively gets treated like this:

interfaces = [ 'eth0', 'capability=RSS', 'speed=10000000000' ]

So the extra properties get treated as interface names but since it can't match them to anything, it silently drops them on the floor. (One of the higher log levels does mention that they couldn't be matched to anything.)

The code to parse the extra properties is all in there, but it is non-functional due to how the tokens are separated before being handled by interpret_interface().

The simplest fix would probably be to use different delimiters than semicolon and comma. I chose pipe for my use case:

https://git.uplinklabs.net/steven/projects/archlinux/misc-packages.git/tree/samba/0001-interface-treat-as-separator-for-parameters.patch?id=98dfa667c37d7132dcfb5471c7da3a96c2dea337

e.g. "interfaces = lan0|capability=RSS|speed=10000000000"

Comma would be ambiguous in this context anyway, as I know I've seen smb.conf files with e.g. "interfaces = eth0,eth1" and such. Maybe the pipe isn't the best replacement for delimiting the properties, but it worked for me.


Another issue with handling these extra properties, delimiter issues aside, is that they would be ignored when appended to named interfaces, e.g. "interfaces = eth0;capability...". The properties only correctly apply where IP addresses are used instead. So I patched that too:

https://git.uplinklabs.net/steven/projects/archlinux/misc-packages.git/tree/samba/0002-interface-allow-overriding-speed-cap-if_index-for-na.patch?id=98dfa667c37d7132dcfb5471c7da3a96c2dea337


I'm also considering writing a patch to auto-detect the "RSS" capability, because it currently never set unless explicitly specified in the "interfaces" line (which isn't possible right now due to the delimiter issue). Detecting it would probably be as simple as looking in /sys/class/net/$interfacename/queues and seeing if there is more than one directory starting with "rx-". We could also populate the field currently marked as "reserved" in fsctl_net_iface_info with the number of RSS queues we found. According to Wireshark, the "reserved" field is used to encode the RSS queue count, though filling it is apparently not necessary to make Windows clients successfully negotiate multi-channel sessions.