Re: [dpdk-dev] [PATCH] igb_uio: allow multi-process access

[Stephen Hemminger <stephen@networkplumber.org>]

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")


Yes, this makes sense.

> 
> 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;

Simple unsigned reference count is not SMP safe on all architectures.
In kernel it is recommended to use refcount_t and associated API's.
Note: refcount_t was introduced in last 2 years and some DPDK users
still have ancient kernels.

>  };
>  
>  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)
> +		return 0;

Do not use (unnecessary) parenthesis. C precedence order is well defined.


>  	/* 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);
>