netdev - Re: [PATCH net-next 01/12] net: homa: define user-visible API for Homa

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Message-ID: <fc86b958-3e31-42f6-a174-3ea7c7fc3377@lunn.ch>
Date: Fri, 1 Nov 2024 19:01:09 +0100
From: Andrew Lunn <andrew@...n.ch>
To: John Ousterhout <ouster@...stanford.edu>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH net-next 01/12] net: homa: define user-visible API for
 Homa

On Fri, Nov 01, 2024 at 10:47:20AM -0700, John Ousterhout wrote:
> On Wed, Oct 30, 2024 at 5:41 AM Andrew Lunn <andrew@...n.ch> wrote:
> >
> > > > Did you build for 32 bit systems?
> > >
> > > Sadly no: my development system doesn't currently have any
> > > cross-compiling versions of gcc :-(
> >
> > I'm not sure in this case it is actually a cross compile. Your default
> > amd64 tool chain should also be able to compile for i386.
> >
> > export ARCH=i386
> > unset CROSS_COMPILE
> > make defconfig
> > make
> 
> Thanks for this additional information. I have now compiled Homa
> (along with the rest of the kernel) for ARCH=i386; in the process I
> learned about uintptr_t and do_div.
> 

> Question: is the distinction between the types u64 and __u64
> significant? If so, is there someplace where it is explained when I
> should use each? So far I have been using __u64 (almost) everywhere.

/include/uapi/asm-generic/int-ll64.h says:

/*
 * __xx is ok: it doesn't pollute the POSIX namespace. Use these in the
 * header files exported to user space
 */

So for files you export to userspace, anything in include/uapi, you
should be using __u64. In the kernel, i think it does not matter, and
i did find:

typedef __u64 u64;

so they probably end up identical. u64 seems more popular in net/ than
__u64, probably because it is shorter.

	Andrew