[RFC PATCH 1/3] ethdev: add set link state on close API

[Ivan Malov]

Hi Ciara,

On Fri, 29 Aug 2025, Ciara Loftus wrote:

> Allow the user to configure the state a link should be in after
> the device has been stopped/closed. Make this configurable
> through the new experimental rte_eth_dev_set_link_state_on_close
> API. Three states are allowed:
> 1. down: bring (or keep) the link down
> 2. up: bring (or keep) the link up
> 3. initial: restore the link to the state it was in when the device was
> started.
>

Perhaps it pays to name it 'status' instead of 'state', as the latter is not
confined to just 'up/down' but also includes the speed, technology, FEC, etc.

As for the three cases:

(3)
When the driver gets probed, it may discover the link being in some state that
the previous driver left us, (A). Then if the user does not invoke any APIs to
tweak the link settings and proceeds straight to 'rte_eth_dev_start', the link
will be in some best-effort state (B). Otherwise it will be in other state, (C).

Which one is implied by 'when the device was started'?

(2)
Does 'keep' describe the link being up prior to 'close'? If so, then if the
link is not 'up' prior to 'close', this commands to bring it up, which may
not be possible if the link partner is gone or the cable is unplugged.

(1)
This is OK. If the driver is capable to force link down, in electrical idle,
it will do that. If it can't do this, the whole API won't be supported.

Thank you.