netdev - Re: [PATCH v3 3/3] IB/ipoib: Log sysfs 'dev

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Date:   Fri, 07 Sep 2018 13:14:37 -0400
From:   Doug Ledford <dledford@...hat.com>
To:     Leon Romanovsky <leon@...nel.org>,
        Arseny Maslennikov <ar@...msu.ru>
Cc:     linux-rdma@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>,
        netdev@...r.kernel.org
Subject: Re: [PATCH v3 3/3] IB/ipoib: Log sysfs 'dev_id' accesses from
 userspace

On Thu, 2018-09-06 at 16:03 +0300, Leon Romanovsky wrote:
> On Thu, Sep 06, 2018 at 10:04:33AM +0300, Arseny Maslennikov wrote:
> > On Wed, Sep 05, 2018 at 04:50:35PM +0300, Leon Romanovsky wrote:
> > > On Mon, Sep 03, 2018 at 07:13:16PM +0300, Arseny Maslennikov wrote:
> > > > Signed-off-by: Arseny Maslennikov <ar@...msu.ru>
> > > > ---
> > > >  drivers/infiniband/ulp/ipoib/ipoib_main.c | 38 +++++++++++++++++++++++
> > > >  1 file changed, 38 insertions(+)
> > > > 
> > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > > index 30f840f874b3..7386e5bde3d3 100644
> > > > --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > > @@ -2386,6 +2386,42 @@ int ipoib_add_pkey_attr(struct net_device *dev)
> > > >  	return device_create_file(&dev->dev, &dev_attr_pkey);
> > > >  }
> > > > 
> > > > +/*
> > > > + * We erroneously exposed the iface's port number in the dev_id
> > > > + * sysfs field long after dev_port was introduced for that purpose[1],
> > > > + * and we need to stop everyone from relying on that.
> > > > + * Let's overload the shower routine for the dev_id file here
> > > > + * to gently bring the issue up.
> > > > + *
> > > > + * [1] https://www.spinics.net/lists/netdev/msg272123.html
> > > > + */
> > > > +static ssize_t dev_id_show(struct device *dev,
> > > > +			   struct device_attribute *attr, char *buf)
> > > > +{
> > > > +	struct net_device *ndev = to_net_dev(dev);
> > > > +	ssize_t ret = -EINVAL;
> > > > +
> > > > +	if (ndev->dev_id == ndev->dev_port) {
> > > > +		netdev_info_once(ndev,
> > > > +			"\"%s\" wants to know my dev_id. "
> > > > +			"Should it look at dev_port instead?\n",
> > > > +			current->comm);
> > > > +		netdev_info_once(ndev,
> > > > +			"See Documentation/ABI/testing/sysfs-class-net for more info.\n");
> > > > +	}
> > > > +
> > > > +	ret = sprintf(buf, "%#x\n", ndev->dev_id);
> > > > +
> > > > +	return ret;
> > > > +}
> > > > +static DEVICE_ATTR_RO(dev_id);
> > > > +
> > > 
> > > I don't see this field among exposed by IPoIB, why should we expose it now?
> > > 
> > 
> > To deviate from standard netdev behaviour, which only prints the
> > field out. Doug wanted this to also print a deprecation message, and
> > netdev (obviously) does not do that. See below.
> > 
> > > > +int ipoib_intercept_dev_id_attr(struct net_device *dev)
> > > > +{
> > > > +	device_remove_file(&dev->dev, &dev_attr_dev_id);
> > > > +	return device_create_file(&dev->dev, &dev_attr_dev_id);
> > > 
> > > Why isn't enough to rely on netdev code?
> > > 
> > 
> > Netdev code relies on macros around a *static* function 'netdev_show',
> > which is defined in net/core/net-sysfs.c; it is not listed in any header
> > files, and the macros aren't as well. This all leads me to believe it
> > was not really meant to be used from outside net/core/net-sysfs.
> > 
> > The only way we could use any netdev code here is to set up our own
> > handler (again), printk() a message, then call netdev_show — but we have
> > no access to it.
> > 
> > Of course, it also may be that I'm terribly missing a clue.
> 
> Thanks,
> 
> IMHO, the end result of adequate Doug's request is a little bit too much.
> I don't think that it justifies such remove->create construction.
> 
> Personal opinion.

I agree with you that the end result is kinda bulky, *but*, we will need
to know if there are things using the old dev_id before we can remove
it.  In particular, I'm concerned the IPoIB handling code of
NetworkManager uses it.  It's worth the cost I think.

-- 
Doug Ledford <dledford@...hat.com>
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