linux-kernel - Re: [RFC PATCH 04/13] switchtec: add link event notifier block

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Message-ID: <20170617051429.GF6040@kroah.com>
Date:   Sat, 17 Jun 2017 07:14:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-ntb@...glegroups.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <Allen.Hubbe@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kurt Schwemmer <kurt.schwemmer@...rosemi.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 04/13] switchtec: add link event notifier block

On Thu, Jun 15, 2017 at 02:37:20PM -0600, Logan Gunthorpe wrote:
> In order for the switchtec NTB code to handle link change events we
> create a notifier block in the switchtec code which gets called
> whenever an appropriate event interrupt occurs.
> 
> In order to preserve userspace's ability to follow these events,
> we compare the event count with a stored copy from last time we
> checked.
> 
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Reviewed-by: Stephen Bates <sbates@...thlin.com>
> Reviewed-by: Kurt Schwemmer <kurt.schwemmer@...rosemi.com>
> ---
>  drivers/pci/switch/switchtec.c | 53 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/switchtec.h      |  5 ++++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/drivers/pci/switch/switchtec.c b/drivers/pci/switch/switchtec.c
> index e9bf17b1934e..63e305b24fb9 100644
> --- a/drivers/pci/switch/switchtec.c
> +++ b/drivers/pci/switch/switchtec.c
> @@ -972,6 +972,50 @@ static const struct file_operations switchtec_fops = {
>  	.compat_ioctl = switchtec_dev_ioctl,
>  };
>  
> +static void link_event_work(struct work_struct *work)
> +{
> +	struct switchtec_dev *stdev;
> +
> +	stdev = container_of(work, struct switchtec_dev, link_event_work);
> +
> +	dev_dbg(&stdev->dev, "%s\n", __func__);

You do know about ftrace, right?  It's good to drop debugging code like
this for "final" versions.

> +
> +	blocking_notifier_call_chain(&stdev->link_notifier, 0, stdev);
> +}

Do you really need a notifier call chain?  How many different things are
going to "hook up" to this?  I ask as they tend to get really messy over
time while direct callbacks are easier to handle and manage.

thanks,

greg k-h