linux-kernel - Re: [PATCH net-next v15 10/14] tcp: RX path for devmem TCP

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Date: Tue, 2 Jul 2024 11:14:53 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org, 
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Subject: Re: [PATCH net-next v15 10/14] tcp: RX path for devmem TCP

On Tue, Jul 2, 2024 at 8:25 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, Jun 28, 2024, at 02:32, Mina Almasry wrote:
> > --- a/arch/alpha/include/uapi/asm/socket.h
> > +++ b/arch/alpha/include/uapi/asm/socket.h
> > @@ -140,6 +140,11 @@
> >  #define SO_PASSPIDFD         76
> >  #define SO_PEERPIDFD         77
> >
> > +#define SO_DEVMEM_LINEAR     78
> > +#define SCM_DEVMEM_LINEAR    SO_DEVMEM_LINEAR
> > +#define SO_DEVMEM_DMABUF     79
> > +#define SCM_DEVMEM_DMABUF    SO_DEVMEM_DMABUF
>
> Something is still wrong with the number assignment:
>
> > --- a/arch/mips/include/uapi/asm/socket.h
> > +++ b/arch/mips/include/uapi/asm/socket.h
> > @@ -151,6 +151,11 @@
> >  #define SO_PASSPIDFD         76
> >  #define SO_PEERPIDFD         77
> >
> > +#define SO_DEVMEM_LINEAR     78
> > +#define SCM_DEVMEM_LINEAR    SO_DEVMEM_LINEAR
> > +#define SO_DEVMEM_DMABUF     79
> > +#define SCM_DEVMEM_DMABUF    SO_DEVMEM_DMABUF
> > +
> >  #if !defined(__KERNEL__)
> >
> >  #if __BITS_PER_LONG == 64
>
> so alpha and mips use the same numbering system as
> the generic version for existing numbers
>
> > diff --git a/arch/parisc/include/uapi/asm/socket.h
> > b/arch/parisc/include/uapi/asm/socket.h
> > index be264c2b1a117..2b817efd45444 100644
> > --- a/arch/parisc/include/uapi/asm/socket.h
> > +++ b/arch/parisc/include/uapi/asm/socket.h
> > @@ -132,6 +132,11 @@
> >  #define SO_PASSPIDFD         0x404A
> >  #define SO_PEERPIDFD         0x404B
> >
> > +#define SO_DEVMEM_LINEAR     78
> > +#define SCM_DEVMEM_LINEAR    SO_DEVMEM_LINEAR
> > +#define SO_DEVMEM_DMABUF     79
> > +#define SCM_DEVMEM_DMABUF    SO_DEVMEM_DMABUF
>
> parisc uses a different number, but you start using the
> generic version here. This is probably fine but needs
> a comment.
>
> > index 8ce8a39a1e5f0..25a2f5255f523 100644
> > --- a/include/uapi/asm-generic/socket.h
> > +++ b/include/uapi/asm-generic/socket.h
> > @@ -135,6 +135,11 @@
> >  #define SO_PASSPIDFD         76
> >  #define SO_PEERPIDFD         77
> >
> > +#define SO_DEVMEM_LINEAR     98
> > +#define SCM_DEVMEM_LINEAR    SO_DEVMEM_LINEAR
> > +#define SO_DEVMEM_DMABUF     99
> > +#define SCM_DEVMEM_DMABUF    SO_DEVMEM_DMABUF
>
> These on the other hand look like a typo: did you
> mean number 78 and 79 instead of 98 and 99?
>

Ooops, I think this is a typo or error indeed. I will fix.

> Alternatively, you could continue with number 87,
> which is the next unused number on sparc, and have
> the same numbers on all architectures?
>

I don't know enough about the tradeoffs of either approach to be
honest, so I'll do what you prefer. I think I'll just fix the ones in
asm-generic/socket.h since that is what we aligned on from previous
iterations I believe, unless you tell me to do differently.

-- 
Thanks,
Mina