From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Date: Tue, 04 May 2010 16:08:23 +0000 Subject: Re: [RFC][PATCH resend 8/12] asm-generic: bitops: introduce le bit Message-Id: <4BE04677.4060608@redhat.com> List-Id: References: <20100504215645.6448af8f.takuya.yoshikawa@gmail.com> <20100504220500.7695cd66.takuya.yoshikawa@gmail.com> <201005041703.00549.arnd@arndb.de> In-Reply-To: <201005041703.00549.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Arnd Bergmann Cc: Takuya Yoshikawa , mtosatti@redhat.com, agraf@suse.de, yoshikawa.takuya@oss.ntt.co.jp, fernando@oss.ntt.co.jp, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-ia64@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, benh@kernel.crashing.org, paulus@samba.org, linuxppc-dev@ozlabs.org, linux-arch@vger.kernel.org, linux-kernel@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