From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit offset macro Date: Tue, 04 May 2010 19:08:23 +0300 Message-ID: <4BE04677.4060608@redhat.com> References: <20100504215645.6448af8f.takuya.yoshikawa@gmail.com> <20100504220500.7695cd66.takuya.yoshikawa@gmail.com> <201005041703.00549.arnd@arndb.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Cc: linux-arch@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, kvm-ia64@vger.kernel.org, fernando@oss.ntt.co.jp, mtosatti@redhat.com, agraf@suse.de, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, yoshikawa.takuya@oss.ntt.co.jp, linuxppc-dev@ozlabs.org, mingo@redhat.com, paulus@samba.org, hpa@zytor.com, tglx@linutronix.de, Takuya Yoshikawa To: Arnd Bergmann Return-path: In-Reply-To: <201005041703.00549.arnd@arndb.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org List-Id: kvm.vger.kernel.org On 05/04/2010 06:03 PM, Arnd Bergmann wrote: > On Tuesday 04 May 2010, Takuya Yoshikawa wrote: > >> Although we can use *_le_bit() helpers to treat bitmaps le arranged, >> having le bit offset calculation as a seperate macro gives us more freedom. >> >> For example, KVM has le arranged dirty bitmaps for VGA, live-migration >> and they are used in user space too. To avoid bitmap copies between kernel >> and user space, we want to update the bitmaps in user space directly. >> To achive this, le bit offset with *_user() functions help us a lot. >> >> So let us use the le bit offset calculation part by defining it as a new >> macro: generic_le_bit_offset() . >> > Does this work correctly if your user space is 32 bits (i.e. unsigned long > is different size in user space and kernel) in both big- and little-endian > systems? > > I'm not sure about all the details, but I think you cannot in general share > bitmaps between user space and kernel because of this. > That's why the bitmaps are defined as little endian u64 aligned, even on big endian 32-bit systems. Little endian bitmaps are wordsize agnostic, and u64 alignment ensures we can use long-sized bitops on mixed size systems. -- error compiling committee.c: too many arguments to function