Re: Making rte_eal_pci_probe() in rte_eal_init() optional?

["Roger B. Melton" <rmelton@cisco.com>]

Hi Thomas, in-line  -Roger

On 11/17/15 10:46 AM, Thomas Monjalon wrote:
> 2015-11-17 08:56, Roger B. Melton:
>> Hi David,  in-line -Roger
>>
>> On 11/16/15 4:46 AM, David Marchand wrote:
>>> Hello Roger,
>>>
>>> On Sun, Nov 15, 2015 at 3:45 PM, Roger B. Melton <rmelton@cisco.com
>>> <mailto:rmelton@cisco.com>> wrote:
>>>
>>>      I like the "-b all" and "-w none" idea, but I think it might be
>>>      complicated to implement it the way we would need it to work.  The
>>>      existing -b and -w options  persist for the duration of the
>>>      application, and we would need the "-b all"/"-w none" to persists
>>>      only through rte_eal_init() time.  Otherwise our attempt to to
>>>      attach a device at a later time would be blocked by the option.
>>>
>>> I agree, the black/white lists should only apply to initial scan.
>>> I forgot about this problem ...
>>> I had started some cleanup in the pci scan / attach code but this is
>>> too late for 2.2, I will post this in the next merge window.
>>>
>>>
>>>      Wouldn't it be simpler to have an option to disable the
>>>      rte_eal_init() time the probe.  Would that address the issue with
>>>      VFIO, prevent automatically attaching to devices while permitting
>>>      on demand attach?
>>>
>>>
>>> I suppose we can do this yes (I think Thomas once proposed off-list an
>>> option like --no-pci-scan).
>>> Do you think you can send a patch ?
>> What about --no-pci-init-probe?  I know it's long, but it is more
>> descriptive of it's purpose to disable only the init time pci probe.
> Why not a "-b all"?
> Making it work would also solve the case where you to scan only part of
> the devices and initialize the blacklisted ones later.
> .
>
Do you envision "-b all" setting a flag that would be used to block 
rte_eal_init() invocation of rte_eal_pci_probe()?  e.g. If we have a new 
API, *rte_eal_pci_blacklist_all_get()* that returns a non-zero value if 
"-b all" was specified, then in rte_eal_init() we would have something like:

...
     /* Probe & Initialize PCI devices */
*    if (!rte_eal_pci_blacklist_all_get())**  <--- New check*
         if (rte_eal_pci_probe())
             rte_panic("Cannot probe PCI\n");
...


Or setting a flag that would be checked in rte_eal_probe_one() similar 
to the existing per device blacklist check?  e.g. Again with a new API, 
*rte_eal_pci_blacklist_all_get()* that returns a non-zero value if "-b 
all" was specified, then in rte_eal_pci_probe_one_driver() we would have 
something like:

         /* no initialization when blacklisted, return without error */
         if (*rte_eal_pci_blacklist_all_get() ||  <--- New check*
             (dev->devargs != NULL &&
              dev->devargs->type == RTE_DEVTYPE_BLACKLISTED_PCI)) {
             RTE_LOG(DEBUG, EAL, "  Device is blacklisted, not 
initializing\n");
             return 1;
         }

The former would work, but I think it would be confusing for "-b all" to 
only apply to init.

The latter would be consistent with how "-b <PCI DBDF>" works, but in 
order to initialize devices at a later time, we would need a way to 
clear the blacklist all state at run time so that 
*rte_eal_pci_blacklist_all()* would return false. For example, something 
like *rte_eal_pci_blacklist_all_clear()*.

Or do you have something else in mind entirely?