quoted

quoted

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We already support this for IPv6, we can do that also for IPv4, but
this syntax may not be trivially expected for ipv4?

I tried this for IPv6 and it doesn't work. Here's what I get:
$ sudo nvme discover -g -G -t tcp -s 8009 -a fe80::800:27ff:fe00:0
Failed to write to /dev/nvme-fabrics: Invalid argument $ sudo nvme
discover -g -G -t tcp -s 8009 -a fe80::800:27ff:fe00:0%enp0s8 Failed
to write to /dev/nvme-fabrics: Invalid argument $ sudo nvme discover
-g -G -t tcp -s 8009 -a [fe80::800:27ff:fe00:0] failed to resolve
host [fe80::800:27ff:fe00:0] info $ sudo nvme discover -g -G -t tcp
-s 8009 -a [fe80::800:27ff:fe00:0%enp0s8] failed to resolve host
[fe80::800:27ff:fe00:0%enp0s8] info

# nvme discover -t tcp -a fe80::5054:ff:fef1:9f3b -w
fe80::5054:ff:fe28:5edb%enp6s0

Thanks for clarifying the syntax. However, that doesn't work for me.

# nvme discover -t tcp -a fe80::800:27ff:fe00:0 -w
fe80::9266:4855:6cf2:f7e9%enp0s8 Failed to write to /dev/nvme-fabrics:
Connection refused

Are you using the linux target? connection refused means that you don't
have a listener on it, it's not a resolution error.

did you have the target listen on fe80::800:27ff:fe00:0%<intf> ?

Doh! You are correct. In my setup, I run the nvme-cli client on a VM and I run the target (nvmet) on the host computer. I had nvmet configured for "0.0.0.0" instead of "::" (i.e. listen on all interfaces). 

After changing nvmet's configuration, I was able to query the discovery log pages, using this syntax:
nvme discover -t tcp -a fe80::800:27ff:fe00:0 -w fe80::9266:4855:6cf2:f7ea%enp0s8

Note that it doesn't work when I append the interface to the Destination IP address as per RFC4007 (like ping) as follows.
nvme discover -t tcp -a fe80::800:27ff:fe00:0%enp0s8 -w fe80::9266:4855:6cf2:f7ea

quoted

Note that the above syntax does not comply with RFC4007. The '%'

delimiter is supposed to be appended to the Destination IP address and not
the Source Address. In other words, to be RFC4007-compliant, the syntax
should be (using your example):

quoted

# nvme discover -t tcp -a fe80::5054:ff:fef1:9f3b%enp6s0 -w
fe80::5054:ff:fe28:5edb

This tells nvme-cli to connect to a controller at address

fe80::5054:ff:fef1:9f3b using interface enp6s0 for the connection. And set the
Source address to fe80::5054:ff:fe28:5edb.

This also seems to work, not sure that it does what we want though...
nvme discover -t tcp -a fe80::5054:ff:fef1:9f3b%enp6s0 -w
fe80::5054:ff:fe28:5edb%enp6s0

Discovery Log Number of Records 1, Generation counter 5 =====Discovery
Log Entry 0======
trtype:  tcp
adrfam:  ipv6
subtype: nvme subsystem
treq:    not specified, sq flow control disable supported
portid:  3
trsvcid: 8009
subnqn:  testnqn1
traddr:  fe80::5054:ff:fef1:9f3b%enp6s0
sectype: none

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The '%' may be confusing when it comes to other transports as well (e.g.
rdma/fc would have to either reject or ignore it, but regardless of
how we add it that would be the case). Having host-traddr accept
either ip or interface seems the most desirable, however that won't
work if there are 2 interfaces that share multiple ip addresses. So
if this is a requirement we'll probably need to add --host-iface as another

option...

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I don’t grok what you mean by "that won't work if there are 2 interfaces

that share multiple ip addresses". Why not? If one specifies the interface by
its name (e.g. enp0s8), there is no possible confusion even if multiple
interfaces share the same IP addresses.

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The following are some examples of how nvme-cli should work to comply

with RFC4007 and be consistent to the way ping operates.

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Example 1 - IPv4, Specify Interface with -w and let Linux select Source

address:

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nvme discover -t tcp -a 192.168.1.9 -w enp0s8

Example 2 - IPv4, Specify Interface and Source address with repeated -w:
nvme discover -t tcp -a 192.168.1.9 -w enp0s8 -w 192.168.56.103

I meant without the repetitions, which you only need if you have 2 devices
that share more than one address, which again, is not a clear use-case to
me, but without repetitions we won't support that.

I've been thinking about what you said regarding the need to repeat the -w option when two interfaces share the same IP address. I think we're looking at the problem from a different point of view. The current implementation uses an IP address to identify an interface. I, on the other hand, believe that the best way to identify an interface is by its "interface name or index". In previous emails, I provided examples of the problems that may occur when using an IP address to identify an interface. For example, one can assign the same IP address to different interfaces making it impossible to distinguish interfaces by their IP address alone. Another example is that the low level APIs (e.g. setsockopt(SO_BINDTODEVICE) don’t even require the source IP address. They only need the interface name/index. So, why go through the trouble of performing a reverse address lookup to retrieve the interface name/index when the address is not used at all? 

By the way, if nvme-cli/linux-nvme allowed specifying interfaces by name/index, then we would not really need to repeat the -w option unless we also wanted to set the source address at the same time. Setting the source address is a completely different thing from setting the interface. One should be allowed to set one independently from the other, or both, or none.

If you look at how ping is implemented, they do not infer the interface from the IP address. If one wants to force ping to go over an interface, then one must provide the interface by name/index using the -I option. If one wants to change the source IP address (without forcing a specific interface), then one provides the IP address to the -I option. It's simple and intuitive. And ping also supports appending the interface to the Destination IP using the '%' delimiter for IPv6-only as per RFC4007.

I think that nvme-cli/linux-nvme should follow the ping approach. Interfaces should never be inferred from source IP addresses, but instead be clearly identified by their name or index. And setting the source address should be independent from setting the interface.

Regards,
Martin

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Example 3 - IPv6, Specify Interface with'%' delimiter and let Linux select

Source address:

quoted

nvme discover -t tcp -a fe80::800:27ff:fe00:0%enp0s8

Example 4 - IPv6, Specify Interface with -w and let Linux select Source

address:

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nvme discover -t tcp -a fe80::800:27ff:fe00:0 -w enp0s8

Example 5 - IPv6, Specify Interface with'%' delimiter and Source address

with -w:

quoted

nvme discover -t tcp -a fe80::800:27ff:fe00:0%enp0s8 -w
fe80::9266:4855:6cf2:f7e9

Example 6 - IPv6, Specify Interface and Source address with repeated -w:
nvme discover -t tcp -a fe80::800:27ff:fe00:0 -w enp0s8 -w
fe80::9266:4855:6cf2:f7e9

Martin

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