linux-kernel - Re: [PATCH net-next 0/2] Expose netdev name in netdev netlink APIs

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Date: Wed, 21 Feb 2024 11:21:23 -0800
From: Joe Damato <jdamato@...tly.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexei Starovoitov <ast@...nel.org>,
	Amritha Nambiar <amritha.nambiar@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Larysa Zaremba <larysa.zaremba@...el.com>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Sridhar Samudrala <sridhar.samudrala@...el.com>,
	Stanislav Fomichev <sdf@...gle.com>,
	Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net-next 0/2] Expose netdev name in netdev netlink APIs

On Wed, Feb 21, 2024 at 11:09:52AM -0800, Jakub Kicinski wrote:
> On Wed, 21 Feb 2024 07:57:28 -0800 Joe Damato wrote:
> > Greetings:
> > 
> > The netdev netlink APIs currently provide the ifindex of a device
> > associated with the NIC queue or NAPI when the netlink API is used. In
> > order for user applications to map this back to a human readable device
> > name, user applications must issue a subsequent ioctl (SIOCGIFNAME) in
> > order to map an ifindex back to a device name.
> 
> To be clear, if_indextoname() is doing it, right? I wanted to be sure
> the concern is really number of syscalls, not the difficulty in getting
> the name.

It seemed a bit odd to me to require the user to hit different APIs -- one
to get the ifindex and then another to get the name. I didn't realize you
had intentionally left the name out, though.

> > This patch set adds ifname to the API so that when queue or NAPI
> > information is retrieved, the human readable string is included. The netdev
> > netlink YAML spec has been updated to include this field, as well.
> > 
> > This saves the subsequent call to ioctl and makes the netlink information
> > more user friendly. Applications might use this information in conjunction
> > with SO_INCOMING_NAPI_ID to map NAPI IDs to specific NICs with application
> > specific configuration (e.g. NUMA zone and CPU layout information).
> 
> For context, the reason why I left the names out is that they can change
> at any moment, but primarily because there are also altnames now:
> 
> 2: eth0:
> [...]
>     altname enp2s0np0
> 
> Most of the APIs try to accept altnames as well as the "main" name.
> If we propagate the name we'll step back into the rtnetlink naming
> mess :(

OK, I see. I didn't realize this was a thing. I suppose what you are saying
is that we wouldn't want to expose names at all and stick with ifindexes
only, is that right?