Re: [dpdk-dev] [PATCH] net/nfp: fix lock file usage

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/24/2018 3:02 PM, Alejandro Lucero wrote:
> 
> 
> On Thu, May 24, 2018 at 11:18 AM, Ferruh Yigit <ferruh.yigit@intel.com
> <mailto:ferruh.yigit@intel.com>> wrote:
> 
>     On 5/23/2018 5:50 PM, Alejandro Lucero wrote:
>     > 
>     > 
>     > On Wed, May 23, 2018 at 4:57 PM, Ferruh Yigit <ferruh.yigit@intel.com <mailto:ferruh.yigit@intel.com>
>     > <mailto:ferruh.yigit@intel.com <mailto:ferruh.yigit@intel.com>>> wrote:
>     > 
>     >     On 5/23/2018 1:28 PM, Alejandro Lucero wrote:
>     >     > DPDK apps can be executed as non-root users but current NFP lock
>     >     > file for avoiding concurrent accesses to CPP interface is precluding
>     >     > this option or requires to modify system file permissions.
>     >     > 
>     >     > When the NFP device is bound to VFIO, this driver does not allow this
>     >     > concurrent access, so the lock file is not required at all.
>     >     > 
>     >     > OVS-DPDK as executed in RedHat distributions is the main NFP user
>     >     > needing this fix.
>     >     > 
>     >     > Fixes: c7e9729da6b5 ("net/nfp: support CPP")
>     >     > 
>     >     > Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com
>     <mailto:alejandro.lucero@netronome.com>
>     <mailto:alejandro.lucero@netronome.com <mailto:alejandro.lucero@netronome.com>>>
>     > 
>     >     Hi Alejandro,
>     > 
>     >     As far as I understand this is to fix a common use case for nfp, but it looks
>     >     like there is already a workaround and only for non-root users.
>     > 
>     > 
>     > There is a patch submitted to stable versions because this lock was also with
>     > the old NSPU interface, but as far as I know, there is no patch yet for the
>     > current upstream tip.
>     > 
>     >  
>     > 
>     >     What is the priority of the patch, only critical but fixes allowed at this
>     >     point, can we push this one to next release?
>     > 
>     > 
>     > This is critical for us because RedHat wants to support OVS with our card, and
>     > when OVS-DPDK is used, this problem is precluding non-root users to execute
>     > OVS-DPDK.
> 
>     What exactly this lock for? Does it to prevent multiple primary process to
>     access CPP interface?
> 
>     If so this is the know limitation in DPDK, not two separate process can driver
>     same hardware, this is valid for all devices, why adding a lock unique to nfp?
> 
> 
> Time ago I had, by mistake, two different DPDK processes using same device, and
> with UIO, there is no one avoiding this.
> 
> You can bound a device to UIO, igb_uio, and then use two different processes
> opening the /dev/uiox file, and it works. 

But this is not anything specific to nfp, isn't it?

> 
> The VFIO driver does avoid this situation, but this lock is required for UIO.
>