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

["Wang, Xiao W" <xiao.w.wang@intel.com>]

Hi,

> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Tuesday, December 12, 2017 9:39 AM
> To: Wang, Xiao W <xiao.w.wang@intel.com>
> Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH] igb_uio: allow multi-process access
> 
> 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.

I think atomic_t associated API will be enough, without worry about kernel version.

> 
> >  };
> >
> >  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.

Agree. Will change it in v2.

Thanks for your comments,
Xiao