netdev - Re: [PATCH rdma-next 1/5] RDMA/core: Provide getter and setter to access IB device name

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Message-ID: <20180920164039.GM3519@mtr-leonro.mtl.com>
Date:   Thu, 20 Sep 2018 19:40:39 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        linux-s390@...r.kernel.org, Ursula Braun <ubraun@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Selvin Xavier <selvin.xavier@...adcom.com>,
        Steve Wise <swise@...lsio.com>, Lijun Ou <oulijun@...wei.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Ariel Elior <Ariel.Elior@...ium.com>,
        Christian Benvenuti <benve@...co.com>,
        Adit Ranadive <aditr@...are.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>
Subject: Re: [PATCH rdma-next 1/5] RDMA/core: Provide getter and setter to
 access IB device name

On Thu, Sep 20, 2018 at 09:15:41AM -0600, Jason Gunthorpe wrote:
> On Thu, Sep 20, 2018 at 02:21:58PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...lanox.com>
> >
> > Prepare IB device name field to rename operation by ensuring that all
> > accesses to it are protected with lock and users don't see part of name.
>
> Oh dear, no, that isn't going to work, there is too much stuff using
> dev_name.. Did you read the comment on device_rename??
>
> https://elixir.bootlin.com/linux/v4.19-rc4/source/drivers/base/core.c#L2715

Yes, I read, it was mentioned in the cover letter.

>
> > The protection is done with global device_lock because it is used in
> > allocation and deallocation phases. At this stage, this lock is not
> > busy and easily can be moved to be per-device, once it will be needed.
> >
> > Signed-off-by: Leon Romanovsky <leonro@...lanox.com>
> >  drivers/infiniband/core/device.c | 24 +++++++++++++++++++++++-
> >  include/rdma/ib_verbs.h          |  8 +++++++-
> >  2 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c
> > index 5a680a88aa87..3270cde6d806 100644
> > +++ b/drivers/infiniband/core/device.c
> > @@ -170,6 +170,14 @@ static struct ib_device *__ib_device_get_by_name(const char *name)
> >  	return NULL;
> >  }
> >
> > +void ib_device_get_name(struct ib_device *ibdev, char *name)
> > +{
> > +	down_read(&lists_rwsem);
> > +	strlcpy(name, ibdev->name, IB_DEVICE_NAME_MAX);
> > +	up_read(&lists_rwsem);
> > +}
> > +EXPORT_SYMBOL(ib_device_get_name);
>
> I think we have to follow netdev and just rely on device_rename()
> being 'good enough'.
>
> Switch everything to use dev_name()/etc rather than try and do
> something like this so the responsibility is on the device core to
> keep this working, not us.
>
> Turns out I have a series for that for unrelated reasons..

And what should I do now with this knowledge?

>
> >  static int alloc_name(char *name)
> >  {
> >  	unsigned long *inuse;
> > @@ -202,6 +210,21 @@ static int alloc_name(char *name)
> >  	return 0;
> >  }
> >
> > +int ib_device_alloc_name(struct ib_device *ibdev, const char *pattern)
> > +{
> > +	int ret = 0;
> > +
> > +	mutex_lock(&device_mutex);
> > +	strlcpy(ibdev->name, pattern, IB_DEVICE_NAME_MAX);
> > +	if (strchr(ibdev->name, '%'))
> > +		ret = alloc_name(ibdev->name);
> > +
> > +	mutex_unlock(&device_mutex);
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL(ib_device_alloc_name);
>
> Can't call alloc_name() without also adding to the list, this will
> allow duplicates.

I planned to change it in the future by moving to different name scheme
with unique naming.

>
> Jason

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