On Fri, Jul 08, 2022 at 04:04:05PM +0100, Matthew Wilcox wrote:
> On Fri, Jul 08, 2022 at 07:57:10AM -0700, Ira Weiny wrote:
> > > > I'll update this to be more clear in a V1 if it goes that far. But to clarify
> > > > here; the protocol information is a u16 vendor id and u8 protocol number. So
> > > > we are able to store that in the unsigned long value that would normally be a
> > > > pointer to something in the XArray.
> > >
> > > Er. Signed long.
> >
> > Sorry I misspoke, xa_mk_value() takes an unsigned long.
>
> It does, *but* ...
>
> static inline void *xa_mk_value(unsigned long v)
> {
> WARN_ON((long)v < 0);
> return (void *)((v << 1) | 1);
> }
>
> ... you can't pass an integer that has the top bit set to it.
>
> > Can't I use xa_mk_value() to store data directly in the entry "pointer"?
>
> Yes, that's the purpose of xa_mk_value(). From what you said, it sounded
> like you were just storing the integer directly, which won't work.
>
> > +static void *pci_doe_xa_prot_entry(u16 vid, u8 prot)
> > +{
> > + return xa_mk_value(((unsigned long)vid << 16) | prot);
> > +}
> >
> > Both Dan and I thought this was acceptable in XArray?
>
> You haven't tested that on 32-bit, have you? Shift vid by 8 instead of
> 16, and it'll be fine.
Ah ok.
>
> (Oh, and you don't need to cast vid; the standard C integer promotions
> will promote vid to int before shifting, and you won't lose any bits)
Will do, thanks!
Ira
