gve: Add feature to adjust RX/TX queue counts

[veethebee_google.com]

Summary

This change introduces new sysctl handlers that allow the user to change
RX/TX queue counts. As before, the default queue counts will be the max
value the device can support. When chaning queue counts, the interface turns
down momentarily while allocating/freeing resources as necessary.

Signed-off-by: Vee Agarwal <[e-mail]>

[veethebee_google.com]

Update man page

[veethebee_google.com]

Set priv rx/tx fields to NULL after free

[markj]

share/man/man4/gve.4

241

It'd be nicer IMO to document the two sysctls together rather than effectively duplicating the description.

243

sys/dev/gve/gve_main.c

214

Please use C-style /* */ comments in the kernel.

568

Why do we alloc resources for max_queues queues instead of num_queues queues?

sys/dev/gve/gve_sysctl.c

288

369

I would suggest using a plain CTLTYPE_UINT instead of constraining the queue count to 16. It feels a bit strange to encode the type of max_queues in the sysctl ABI. For command-line usage it doesn't matter, but for consistency with other NIC drivers it might be nicer to use a more generic type when accessing the sysctl from C.

370

374

[veethebee_google.com]

Fix from comments

[markj]

Seems ok to me modulo the comments.

sys/dev/gve/gve_sysctl.c

329

IMO printing a message in this case is overkill and not typical for sysctl handlers. The sysctl handler will return the current number of queues currently configured, so code which modifies the queue count can see how many queues were registered before.

359

Same comment here about the print.

[veethebee_google.com]

Don't log if queue count doesn't change