linux-kernel - Re: [RFC PATCH net-next 4/7] net: ethtool: add a netlink command to list PHYs

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Message-ID: <72a5cd8f-d776-479c-9d7f-191900d19342@lunn.ch>
Date:   Tue, 12 Sep 2023 18:01:10 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Nicolò Veronese <nicveronese@...il.com>,
        thomas.petazzoni@...tlin.com,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [RFC PATCH net-next 4/7] net: ethtool: add a netlink command to
 list PHYs

On Thu, Sep 07, 2023 at 02:16:35PM +0200, Maxime Chevallier wrote:
> Hello Russell,
> 
> On Thu, 7 Sep 2023 11:00:24 +0100
> "Russell King (Oracle)" <linux@...linux.org.uk> wrote:
> 
> > On Thu, Sep 07, 2023 at 11:24:02AM +0200, Maxime Chevallier wrote:
> > > +#define PHY_MAX_ENTRIES	16
> > > +
> > > +struct phy_list_reply_data {
> > > +	struct ethnl_reply_data		base;
> > > +	u8 n_phys;
> > > +	u32 phy_indices[PHY_MAX_ENTRIES];  
> > 
> > Please could you detail the decision making behind 16 entries - is this
> > arbitary or based on something?
> > 
> > Also, please consider what we should do if we happen to have more than
> > 16 entries.
> 
> Ah indeed it was totally arbitrary, the idea was to have a fixed-size
> reply struct, so that we can populate the
> ethnl_request_ops.reply_data_size field and not do any manual memory
> management. But I can store a pointer to the array of phy devices,
> dynamically allocated and we won't have to deal with this fixed,
> arbitrary-sized array anymore.

I think Jakub already commented on this somewhere, but netlink should
allow for arbitrary long lists.

      Andrew