Re: [PATCH] pci: fix check uio bind

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

On Sat, Oct 21, 2017 at 12:47:14AM +0800, Tan, Jianfeng wrote:
> Hi Gaëtan,
> 
> 
> On 10/19/2017 7:42 PM, Gaëtan Rivet wrote:
> >Hi Jianfeng,
> >
> >On Thu, Oct 19, 2017 at 11:18:29AM +0000, Jianfeng Tan wrote:
> >>When checking if any devices bound to uio, we did not exclud
> >>those which are blacklisted (or in the case that a whitelist
> >>is specified).
> >>
> >>This patch fixes it by only checking whitelisted devices.
> >>
> >>Fixes: 815c7deaed2d ("pci: get IOMMU class on Linux")
> >>
> >>Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
> >>---
> >>  lib/librte_eal/linuxapp/eal/eal_pci.c | 18 ++++++++++++++++++
> >>  1 file changed, 18 insertions(+)
> >>
> >>diff --git a/lib/librte_eal/linuxapp/eal/eal_pci.c b/lib/librte_eal/linuxapp/eal/eal_pci.c
> >>index b4dbf95..2b23d67 100644
> >>--- a/lib/librte_eal/linuxapp/eal/eal_pci.c
> >>+++ b/lib/librte_eal/linuxapp/eal/eal_pci.c
> >>@@ -516,8 +516,26 @@ static inline int
> >>  pci_one_device_bound_uio(void)
> >>  {
> >>  	struct rte_pci_device *dev = NULL;
> >>+	struct rte_devargs *devargs;
> >>+	int check_all = 1;
> >>+	int need_check;
> >>+
> >>+	if (rte_pci_bus.bus.conf.scan_mode == RTE_BUS_SCAN_WHITELIST)
> >>+		check_all = 0;
> >>  	FOREACH_DEVICE_ON_PCIBUS(dev) {
> >>+		devargs = dev->device.devargs;
> >>+
> >>+		need_check = 0;
> >>+		if (check_all)
> >Unless I'm mistaken, you will check blacklisted devices as well here.
> 
> Thank you for pointing out this.
> 
> I was referring to rte_pci_probe(), which also only check "probe_all" and
> (devargs && RTE_DEV_WHITELISTED); but turns out it double checks the
> blacklisted devices in rte_pci_probe_one_driver().
> 
> I'll fix it.
> 
> >The condition should be something like:
> >
> >if (check_all && devargs == NULL)
> 
> >Which means that both ifs can be refactored as
> >
> >if ((check_all ^ (devargs != NULL)) == 0)
> >         continue;
> >
> >Removing need_check. But it can be hard to read.
> 
> Yes, I prefer to make it easy to understand. Please let me know if you are
> OK with below code (remove check_all):
> 
>         FOREACH_DEVICE_ON_PCIBUS(dev) {
>                 devargs = dev->device.devargs;
> 
>                 need_check = 0;
>                 switch (rte_pci_bus.bus.conf.scan_mode) {
>                 case RTE_BUS_SCAN_UNDEFINED:
>                         need_check = 1;
>                         break;
>                 case RTE_BUS_SCAN_WHITELIST:
>                         if (devargs && devargs->policy ==
> RTE_DEV_WHITELISTED)
>                                 need_check = 1;
>                         break;
>                 case RTE_BUS_SCAN_BLACKLIST:
>                         if (!devargs || devargs->policy !=
> RTE_DEV_BLACKLISTED)
>                                 need_check = 1;
>                         break;
>                 }
> 
>                 if (!need_check)
>                         continue;
> ...

I like the switch, two remarks however:

1. The SCAN_UNDEFINED basically means blacklist mode for the PCI bus.
   This is the reason probe_all was set by testing for WHITELIST
   mode: either of the other too would thus trigger the blacklist
   behavior.

   Thus, I think you could write a fallthrough case for UNDEFINED, that
   would go into the BLACKLIST mode.

2. For pointers in general I would test against NULL instead of using
   the unary '!'.
   I think it is the general policy in DPDK to always explicitly check
   against the constant value, but I personally think that for booleans
   like need_check the "not" operator is ok.
   So I will only highlight the !devargs :)

> 
> Thanks,
> Jianfeng

-- 
Gaëtan Rivet
6WIND