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Date: Mon, 11 Dec 2017 17:38:55 -0800
From: Stephen Hemminger <stephen@networkplumber.org>
To: Xiao Wang <xiao.w.wang@intel.com>
Cc: ferruh.yigit@intel.com, dev@dpdk.org
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Subject: Re: [dpdk-dev] [PATCH] igb_uio: allow multi-process access
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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")
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);
>