netdev - Re: [PATCH] net-sysfs: expose IRQ number

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Date:   Mon, 29 Apr 2019 18:45:28 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH] net-sysfs: expose IRQ number

On Mon, 29 Apr 2019 at 18:20, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> On Mon, 29 Apr 2019 08:01:07 +0200
> Rafał Miłecki <zajec5@...il.com> wrote:
>
> > From: Rafał Miłecki <rafal@...ecki.pl>
> >
> > Knowing IRQ number makes e.g. reading /proc/interrupts much simpler.
> > It's more reliable than guessing device name used by a driver when
> > calling request_irq().
> >
> > Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> > ---
> > I found a script parsing /proc/interrupts for a given interface name. It wasn't
> > working for me as it assumed request_irq() was called with a device name. It's
> > not a case for all drivers.
> >
> > I also found some other people looking for a proper solution for that:
> > https://unix.stackexchange.com/questions/275075/programmatically-determine-the-irqs-associated-with-a-network-interface
> > https://stackoverflow.com/questions/7516984/retrieving-irq-number-of-a-nic
> >
> > Let me know if this solution makes sense. I can say it works for me ;)
> > ---
> >  Documentation/ABI/testing/sysfs-class-net |  7 +++++++
> >  net/core/net-sysfs.c                      | 16 ++++++++++++++++
> >  2 files changed, 23 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
> > index 664a8f6a634f..33440fe77ca7 100644
> > --- a/Documentation/ABI/testing/sysfs-class-net
> > +++ b/Documentation/ABI/testing/sysfs-class-net
> > @@ -301,3 +301,10 @@ Contact: netdev@...r.kernel.org
> >  Description:
> >               32-bit unsigned integer counting the number of times the link has
> >               been down
> > +
> > +What:                /sys/class/net/<iface>/irq
> > +Date:                April 2019
> > +KernelVersion:       5.2
> > +Contact:     netdev@...r.kernel.org
> > +Description:
> > +             IRQ number used by device
> > diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> > index e4fd68389d6f..a3eb7c3f1f37 100644
> > --- a/net/core/net-sysfs.c
> > +++ b/net/core/net-sysfs.c
> > @@ -512,6 +512,21 @@ static ssize_t phys_switch_id_show(struct device *dev,
> >  }
> >  static DEVICE_ATTR_RO(phys_switch_id);
> >
> > +static ssize_t irq_show(struct device *dev, struct device_attribute *attr,
> > +                     char *buf)
> > +{
> > +     const struct net_device *netdev = to_net_dev(dev);
> > +     ssize_t ret;
> > +
> > +     if (!rtnl_trylock())
> > +             return restart_syscall();
> > +     ret = sprintf(buf, "%d\n", netdev->irq);
> > +     rtnl_unlock();
> > +
> > +     return ret;
> > +}
> > +static DEVICE_ATTR_RO(irq);
> > +
> >  static struct attribute *net_class_attrs[] __ro_after_init = {
> >       &dev_attr_netdev_group.attr,
> >       &dev_attr_type.attr,
> > @@ -542,6 +557,7 @@ static struct attribute *net_class_attrs[] __ro_after_init = {
> >       &dev_attr_proto_down.attr,
> >       &dev_attr_carrier_up_count.attr,
> >       &dev_attr_carrier_down_count.attr,
> > +     &dev_attr_irq.attr,
> >       NULL,
> >  };
> >  ATTRIBUTE_GROUPS(net_class);
>
> Can't you find this on the PCI side already?
> $ ls /sys/class/net/eno1/device/msi_irqs/
> 37  38  39  40  41

I'm dealing with bgmac supported ethernet device on bcma bus (not
PCI). I could make bcma bus provide IRQ numbers, but I thought
something at net subsystem level will be more generic.

I'm going to review Willem's solution/idea for now.

-- 
Rafał