Re: [dpdk-dev] [PATCH] bus/pci: nvme on Windows requires class id and bus

[Nick Connolly <nick.connolly@mayadata.io>]

Hi Tal,

Thanks for the comments.

>> +       /* Try and find PCI class ID */
>> +       for (cp = buf; !(cp[0] == 0 && cp[1] == 0); cp++)
> How about
> for (cp = buf; cp[0] || cp[1]; cp++)
That would be my preferred idiom, but the DPDK coding style (1.9.1) says 
'do not use ! for tests unless it is a boolean' (but somewhat 
confusingly does so in a section on NULL pointers).  I interpreted it as 
a general prohibition on conditionals without an explicit operator 
(except for booleans).  I'd love to be corrected here!

>> +               if (*cp == '&' && sscanf_s(cp, "&CC_%" PRIx32, &class_id) == 1)
> Could there be a case where PCI\\VEN_v(4)&DEV_d(4)&CC_c(2)s(2) exist but PCI\\VEN_v(4)&DEV_d(4)&CC_c(2)s(2)p(2) doesn't? In that case the parsing would be incorrect.
The MSDN documentation says that the most specific string will be 
returned first, in this case &CC_c(2)s(2)p(2), so if there is a 6-digit 
class ID we will return it.  That left me wondering what to do if we 
only encounter a 4-digit class ID.  If we ignore it, then we won't be 
able to match on the class ID.  We could parse it as 4-digits and supply 
zero for the p(2) field, but that left me wondering why Windows wouldn't 
have already done that for us.  What I see on my own systems is that 
there is always a 6-digit class ID defined, even if the pci-ids 
repository doesn't list any values for p(2) (e.g. 
https://pci-ids.ucw.cz/read/PD/07/80 reports as &CC_078000).

My conclusion was that was probably best just to return the first class 
ID that Windows reports even if it's only 4-digits.  That way the device 
can still be found and will match the CC_ info displayed in device manager.

Thanks,
Nick