From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v3 04/41] virtio: memory access APIs Date: Mon, 24 Nov 2014 20:49:09 +0200 Message-ID: <20141124184909.GA19382@redhat.com> References: <1416829787-14252-1-git-send-email-mst@redhat.com> <1416829787-14252-5-git-send-email-mst@redhat.com> <20141124121503.GB14353@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Geert Uytterhoeven Cc: Bjarke Istrup Pedersen , Anup Patel , rusty@au1.ibm.com, Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , virtualization@lists.linux-foundation.org, Sakari Ailus , linux-api@vger.kernel.org, Paolo Bonzini , Pranavkumar Sawargaonkar , David Miller , Alexei Starovoitov List-Id: linux-api@vger.kernel.org On Mon, Nov 24, 2014 at 01:58:43PM +0100, Geert Uytterhoeven wrote: > On Mon, Nov 24, 2014 at 1:15 PM, Michael S. Tsirkin wrote: > > On Mon, Nov 24, 2014 at 01:03:24PM +0100, Geert Uytterhoeven wrote: > >> On Mon, Nov 24, 2014 at 12:52 PM, Michael S. Tsirkin wrote: > >> > virtio 1.0 makes all memory structures LE, so > >> > we need APIs to conditionally do a byteswap on BE > >> > architectures. > >> > > >> > To make it easier to check code statically, > >> > add virtio specific types for multi-byte integers > >> > in memory. > >> > > >> > Add low level wrappers that do a byteswap conditionally, these will be > >> > useful e.g. for vhost. Add high level wrappers that > >> > query device endian-ness and act accordingly. > >> > >> > diff --git a/include/linux/virtio_byteorder.h b/include/linux/virtio_byteorder.h > >> > new file mode 100644 > >> > index 0000000..824ed0b > >> > --- /dev/null > >> > +++ b/include/linux/virtio_byteorder.h > >> > >> > +static inline u16 __virtio16_to_cpu(bool little_endian, __virtio16 val) > >> > +{ > >> > + if (little_endian) > >> > + return le16_to_cpu((__force __le16)val); > >> > + else > >> > + return (__force u16)val; > >> > +} > >> > >> What's wrong with just using le16-to_cpu() ... > > > > le16-to_cpu() is simply wrong: virtio needs to be > > LE or native endian, depending on whether it's running > > in 0.9 or 1.0 mode. > > IC, that was not clear from the description for this patch. > I thought it was dependent on BE architectures. > > Nevertheless, any chance you can get rid of the "conditional"? I don't see how - this is fundamental to any virtio device that wants to support both 0.9 and 1.0 from the same codebase. > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds