Issue configuring bandwidth rate on a certain network interface about tcconfig HOT 1 CLOSED

@dastergon
Thank you for your detailed investigation and the pull request.
That's good to know.
I did not know that the para-virtualized network drivers return -1 to /sys/class/net/<iface>/speed.

ethtool seems to accept SPEED_UNKNOWN (-1):
https://github.com/torvalds/linux/blob/a090bd4ff8387c409732a8e059fbf264ea0bdd56/include/uapi/linux/ethtool.h#L1509

static inline int ethtool_validate_speed(__u32 speed)
{
	return speed <= INT_MAX || speed == SPEED_UNKNOWN;
}

https://github.com/torvalds/linux/blob/a090bd4ff8387c409732a8e059fbf264ea0bdd56/include/uapi/linux/ethtool.h#L1652

 * struct ethtool_link_settings - link control and status
...
 * is up they represent the negotiated link mode; if the link is down,
 * the speed is 0, %SPEED_UNKNOWN or the highest enabled speed and
 * @duplex is %DUPLEX_UNKNOWN or the best enabled duplex mode.

So would it make sense to add a handling in the code to default to the iproute2 upper bound when it encounters a -1 speed?

That makes sense.

I've made some modification for tests (no logic changes), and add test cases.
And now, published at tcconfig 0.13.1.
Thank you for your help.

from tcconfig.