linux-kernel - Re: [RFC,net-next, 2/5] vrf: track associations between VRF devices and tables

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Message-ID: <20200613122859.4f5e2761@hermes.lan>
Date:   Sat, 13 Jun 2020 12:28:59 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Andrea Mayer <andrea.mayer@...roma2.it>
Cc:     David Ahern <dsahern@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Shrijeet Mukherjee <shrijeet@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Donald Sharp <sharpd@...ulusnetworks.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Dinesh Dutt <didutt@...il.com>,
        Stefano Salsano <stefano.salsano@...roma2.it>,
        Paolo Lungaroni <paolo.lungaroni@...t.it>,
        Ahmed Abdelsalam <ahabdels@...il.com>
Subject: Re: [RFC,net-next, 2/5] vrf: track associations between VRF devices
 and tables

On Fri, 12 Jun 2020 18:49:34 +0200
Andrea Mayer <andrea.mayer@...roma2.it> wrote:

> +	/* shared_tables:
> +	 * count how many distinct tables does not comply with the
> +	 * strict mode requirement.
> +	 * shared_table value must be 0 in order to switch to strict mode.
> +	 *
> +	 * example of evolution of shared_table:
> +	 *                                                        | time
> +	 * add  vrf0 --> table 100        shared_tables = 0       | t0
> +	 * add  vrf1 --> table 101        shared_tables = 0       | t1
> +	 * add  vrf2 --> table 100        shared_tables = 1       | t2
> +	 * add  vrf3 --> table 100        shared_tables = 1       | t3
> +	 * add  vrf4 --> table 101        shared_tables = 2       v t4
> +	 *
> +	 * shared_tables is a "step function" (or "staircase function")
> +	 * and is increased by one when the second vrf is associated to a table
> +	 *
> +	 * at t2, vrf0 and vrf2 are bound to table 100: shared_table = 1.
> +	 *
> +	 * at t3, another dev (vrf3) is bound to the same table 100 but the
> +	 * shared_table counters is still 1.
> +	 * This means that no matter how many new vrfs will register on the
> +	 * table 100, the shared_table will not increase (considering only
> +	 * table 100).
> +	 *
> +	 * at t4, vrf4 is bound to table 101, and shared_table = 2.
> +	 *
> +	 * Looking at the value of shared_tables we can immediately know if
> +	 * the strict_mode can or cannot be enforced. Indeed, strict_mode
> +	 * can be enforced iff shared_table = 0.
> +	 *
> +	 * Conversely, shared_table is decreased when a vrf is de-associated
> +	 * from a table with exactly two associated vrfs.
> +	 */
> +	int shared_tables;

Should this be unsigned?
Should it be a fixed size?