From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v6 11/12] KVM: introduce readonly memslot Date: Sun, 09 Sep 2012 15:52:24 +0200 Message-ID: <504C9F18.30904@web.de> References: <5032F8FD.2020306@linux.vnet.ibm.com> <5032FA5B.5040308@linux.vnet.ibm.com> <5049CB36.4080000@siemens.com> <5049D0AA.2060202@linux.vnet.ibm.com> <5049D722.5090305@siemens.com> <504C9CA9.5010708@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigC87A82FE9CE0F9CCCC2C1F29" Cc: Xiao Guangrong , Marcelo Tosatti , LKML , KVM To: Avi Kivity Return-path: In-Reply-To: <504C9CA9.5010708@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigC87A82FE9CE0F9CCCC2C1F29 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 2012-09-09 15:42, Avi Kivity wrote: > On 09/07/2012 02:14 PM, Jan Kiszka wrote: >>> >>> $ grep __KVM_HAVE include/linux/kvm.h | wc -l >>> 20 >> >> Yes, mistakes of the past. >> >>> >>> As your suggestion, userspace will always use the CAP even if the CAP= >>> is not really supported. We do not need care the overload on other ar= ches? >> >> Generally, userspace can only find out if a CAP is supported by testin= g >> during runtime. Sometimes, the CAP may also be used to switch features= >> that are only available on certain archs. But this particular feature >> should surely become a generic one soon, and the code you could skip i= n >> userspace is truly minimal. >=20 > You also need them for build time, to see if the ioctl names and > structures are defined. qemu chose not to do this ifdeffery but we mus= t > not make that choice for other userspace. I disagree. We switched QEMU to the pattern the kernel officially recommends: carry your own headers if you cannot rely on a recent distribution. The only valid use case for #ifdef KVM_CAP is to allow disabling of generic code that only some archs can make use of. I'm not arguing for cleaning up legacy CAPs but for applying this rule on newly introduced ones. Jan --------------enigC87A82FE9CE0F9CCCC2C1F29 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://www.enigmail.net/ iEYEARECAAYFAlBMnx4ACgkQitSsb3rl5xRy1gCdFmyHVBLQzDc/RAG/OGQ+cCTX LGwAoJLNc1I7BpSwQw/8joVYjWHcUOMK =IGA4 -----END PGP SIGNATURE----- --------------enigC87A82FE9CE0F9CCCC2C1F29--