From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH] igb_uio: allow multi-process access
Date: Thu, 8 Mar 2018 13:17:00 -0800
Message-ID: <20180308131700.1569797c@xeon-e3>
References: <1512784653-128951-1-git-send-email-xiao.w.wang@intel.com>
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Cc: ferruh.yigit@intel.com, dev@dpdk.org
To: Xiao Wang <xiao.w.wang@intel.com>
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On Fri,  8 Dec 2017 17:57:33 -0800
Xiao Wang <xiao.w.wang@intel.com> wrote:

> In some case, one device are accessed by different processes via
> different BARs, so one uio device may be opened by more than one
> process, for this case we just need to enable interrupt once, and
> pci_clear_master only when the last process closed.
> 
> Fixes: 5f6ff30dc507 ("igb_uio: fix interrupt enablement after FLR in VM")
> 
> Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> ---
>  lib/librte_eal/linuxapp/igb_uio/igb_uio.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
> index a3a98c1..c239d98 100644
> --- a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
> +++ b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
> @@ -45,6 +45,7 @@ struct rte_uio_pci_dev {
>  	struct uio_info info;
>  	struct pci_dev *pdev;
>  	enum rte_intr_mode mode;
> +	uint32_t ref_cnt;
>  };
>  
>  static char *intr_mode;
> @@ -336,6 +337,9 @@ struct rte_uio_pci_dev {
>  	struct pci_dev *dev = udev->pdev;
>  	int err;
>  
> +	if (++(udev->ref_cnt) > 1)

Minor nit: Parenthesis is unnecessary here.

> +		return 0;
> +
>  	/* set bus master, which was cleared by the reset function */
>  	pci_set_master(dev);
>  
> @@ -354,6 +358,9 @@ struct rte_uio_pci_dev {
>  	struct rte_uio_pci_dev *udev = info->priv;
>  	struct pci_dev *dev = udev->pdev;
>  
> +	if (--(udev->ref_cnt) > 0)
> +		return 0;
> +
>  	/* disable interrupts */
>  	igbuio_pci_disable_interrupts(udev);
>  

You might consider using new reference counting (refcnt_t) in kernel which
protects against accidental under/overflow.