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From: "Belanger, Martin" <Martin.Belanger@dell.com>
To: Hannes Reinecke <hare@suse.de>, Sagi Grimberg <sagi@grimberg.me>,
	Martin Belanger <nitram_67@hotmail.com>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>
Cc: "kbusch@kernel.org" <kbusch@kernel.org>,
	"axboe@fb.com" <axboe@fb.com>, "hch@lst.de" <hch@lst.de>
Subject: RE: [PATCH 1/1] Add 'Transport Interface' (triface) option. This can be used to specify the IP interface to use for the connection. The driver uses that to set SO_BINDTODEVICE on the socket before connecting.
Date: Wed, 12 May 2021 12:12:30 +0000
Message-ID: <SJ0PR19MB454488E95A2A00E5ABC757DBF2529@SJ0PR19MB4544.namprd19.prod.outlook.com> (raw)
In-Reply-To: <2d747a9f-d29d-de1c-7bdc-69e11bf5d9da@suse.de>

> On 5/11/21 7:13 PM, Sagi Grimberg wrote:
> >
> >> 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.
> >
> > I'm starting to think that we are going in circles, I'm getting to the
> > point that having host_iface is the right way to go.
> >
> > We can have nvme-cli convert <addr>%iface notation to
> > "..,host_traddr=<addr>,host_iface=<iface>,.." when creating the
> > controller string...
> 
> That was my thinking, too; the only _other_ way would be to have a
> host_traddr _imply_ a binding to the underlying interface.
> We could define that, but having a single option doing _two_ different
> things is not good software design.
> So let's do the 'host_iface' thingie.
> 
> Cheers,
> 
> Hannes
> --
> Dr. Hannes Reinecke                Kernel Storage Architect
> hare@suse.de                              +49 911 74053 688
> SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809
> (AG Nürnberg), Geschäftsführer: Felix Imendörffer

Thanks Hannes and Sagi. I will resubmit the 'host_iface' patch after running more IPv6 tests. Sagi made me realize that IPv6 has a few subtle differences and I need to double check that the current host_iface implementation works as well for IPv6 as it does for IPv4.
Martin
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Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210415192848.962891-1-nitram_67@hotmail.com>
2021-04-15 19:28 ` Martin Belanger
2021-05-01 11:34   ` Hannes Reinecke
2021-05-03 16:59     ` Belanger, Martin
2021-05-04 13:25       ` Hannes Reinecke
2021-05-04 19:56   ` Sagi Grimberg
2021-05-05  8:47     ` Hannes Reinecke
2021-05-05 14:31       ` Belanger, Martin
2021-05-05 18:33         ` James Smart
2021-05-05 20:32         ` Sagi Grimberg
2021-05-06 18:27           ` Michael Christie
2021-05-06  6:05         ` Hannes Reinecke
2021-05-06  7:00           ` Hannes Reinecke
2021-05-06 15:46             ` Belanger, Martin
2021-05-07 18:20               ` Sagi Grimberg
2021-05-10 13:49                 ` Belanger, Martin
2021-05-10 18:13                   ` Sagi Grimberg
2021-05-10 19:18                     ` Belanger, Martin
2021-05-11  0:28                       ` Sagi Grimberg
2021-05-11 13:41                         ` Belanger, Martin
2021-05-11 17:13                           ` Sagi Grimberg
2021-05-12  6:09                             ` Hannes Reinecke
2021-05-12 12:12                               ` Belanger, Martin [this message]
2021-05-12 22:12                                 ` Sagi Grimberg

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