netdev - Re: [PATCH v4 4/8] PCI: replace pci_dev::driver usage that gets the driver name

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Message-ID: <20210929090401.qvpjng3jne76o6kw@pengutronix.de>
Date:   Wed, 29 Sep 2021 11:04:01 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alexander Duyck <alexanderduyck@...com>,
        oss-drivers@...igine.com, Paul Mackerras <paulus@...ba.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ido Schimmel <idosch@...dia.com>,
        Rafał Miłecki <zajec5@...il.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Uwe Kleine-König <uwe@...ine-koenig.org>,
        Vadym Kochan <vkochan@...vell.com>, Michael Buesch <m@...s.ch>,
        Jiri Pirko <jiri@...dia.com>,
        Salil Mehta <salil.mehta@...wei.com>, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        Taras Chornyi <tchornyi@...vell.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        linux-crypto@...r.kernel.org, kernel@...gutronix.de,
        Oliver O'Halloran <oohall@...il.com>,
        linuxppc-dev@...ts.ozlabs.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v4 4/8] PCI: replace pci_dev::driver usage that gets the
 driver name

Hello Simon,

On Wed, Sep 29, 2021 at 10:05:42AM +0200, Simon Horman wrote:
> On Tue, Sep 28, 2021 at 12:31:29PM +0200, Uwe Kleine-König wrote:
> > On Tue, Sep 28, 2021 at 12:01:28PM +0200, Simon Horman wrote:
> > > On Mon, Sep 27, 2021 at 10:43:22PM +0200, Uwe Kleine-König wrote:
> > > > From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > > 
> > > > struct pci_dev::driver holds (apart from a constant offset) the same
> > > > data as struct pci_dev::dev->driver. With the goal to remove struct
> > > > pci_dev::driver to get rid of data duplication replace getting the
> > > > driver name by dev_driver_string() which implicitly makes use of struct
> > > > pci_dev::dev->driver.
> > > > 
> > > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > 
> > > ...
> > > 
> > > > diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c b/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c
> > > > index 0685ece1f155..23dfb599c828 100644
> > > > --- a/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c
> > > > +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c
> > > > @@ -202,7 +202,7 @@ nfp_get_drvinfo(struct nfp_app *app, struct pci_dev *pdev,
> > > >  {
> > > >  	char nsp_version[ETHTOOL_FWVERS_LEN] = {};
> > > >  
> > > > -	strlcpy(drvinfo->driver, pdev->driver->name, sizeof(drvinfo->driver));
> > > > +	strlcpy(drvinfo->driver, dev_driver_string(&pdev->dev), sizeof(drvinfo->driver));
> > > 
> > > I'd slightly prefer to maintain lines under 80 columns wide.
> > > But not nearly strongly enough to engage in a long debate about it.
> > 
> > :-)
> > 
> > Looking at the output of
> > 
> > 	git grep strlcpy.\*sizeof
> > 
> > I wonder if it would be sensible to introduce something like
> > 
> > 	#define strlcpy_array(arr, src) (strlcpy(arr, src, sizeof(arr)) + __must_be_array(arr))
> > 
> > but not sure this is possible without a long debate either (and this
> > line is over 80 chars wide, too :-).
> 
> My main motivation for the 80 char limit in nfp_net_ethtool.c is
> not that I think 80 char is universally a good limit (although that is true),
> but rather that I expect that is the prevailing style in nfp_net_ethtool.c.

I sent out v5 with an additional line break now.
 
> So a macro more than 80 car wide somewhere else is fine by me.
> 
> However, when running checkpatch --strict over the patch it told me:
> 
>     WARNING: Prefer strscpy over strlcpy - see: https://lore.kernel.org/r/CAHk-=wgfRnXz0W3D37d01q3JFkr_i_uTL=V6A6G1oUZcprmknw@mail.gmail.com/
>     #276: FILE: drivers/net/ethernet/netronome/nfp/nfp_net_ethtool.c:205:
>     +	strlcpy(drvinfo->driver, dev_driver_string(&pdev->dev), sizeof(drvinfo->driver));
> 
>     total: 0 errors, 1 warnings, 0 checks, 80 lines checked
> 
> (Amusingly, more text wider than 80 column, perhaps suggesting the folly of
>  my original comment, but lets move on from that.)
> 
> As your patch doesn't introduce the usage of strlcpy() I was considering a
> follow-up patch to change it to strscpy(). And in general the email at the
> link above suggests all usages of strlcpy() should do so. So perhaps
> creating strscpy_array is a better idea?

What I read about strscpy() is that conversions for the sake of the
conversion are not welcome. When such a conversion comes from someone
involved with the driver that is also tested this is probably fine.
 
> I have not thought about this much, and probably this just leads us to a
> deeper part of the rabbit hole.

I assume so, too.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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