From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33927) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aJOWq-0001nW-RF for qemu-devel@nongnu.org; Wed, 13 Jan 2016 11:44:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aJOWm-0003lg-PU for qemu-devel@nongnu.org; Wed, 13 Jan 2016 11:44:12 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59804) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aJOWm-0003la-Jt for qemu-devel@nongnu.org; Wed, 13 Jan 2016 11:44:08 -0500 References: <567A4EB0.1040807@parallels.com> <1450856816-9816-1-git-send-email-den@openvz.org> <1450856816-9816-2-git-send-email-den@openvz.org> <20160111173106.GL9454@noname.redhat.com> <56949140.1010800@openvz.org> <20160112101031.GB4841@noname.redhat.com> <20160112113331.GA16191@ad.usersys.redhat.com> <569522CF.40504@openvz.org> <20160113001016.GB25517@ad.usersys.redhat.com> From: Eric Blake Message-ID: <56967ED5.9050300@redhat.com> Date: Wed, 13 Jan 2016 09:44:05 -0700 MIME-Version: 1.0 In-Reply-To: <20160113001016.GB25517@ad.usersys.redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="wxl7vrNJWl08bq7UxAVFL8OgR0r3EEVC8" Subject: Re: [Qemu-devel] [PATCH 1/5] block: added lock image option and callback List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng , "Denis V. Lunev" Cc: Kevin Wolf , Olga Krishtal , qemu-devel@nongnu.org, Max Reitz This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --wxl7vrNJWl08bq7UxAVFL8OgR0r3EEVC8 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 01/12/2016 05:10 PM, Fam Zheng wrote: >> If we will switch default in my patch from 'nolock' to 'lock' then >> pour guys which are calling qemu-img etc stuff will see the lock >> as necessary while 'proper management software' aka libvirt >> will be able to call qemu/qemu-img etc with proper 'nolock' >> flag as they do care about the locking. >=20 > That is wrong because then we break old libvirt with the new qemu-img (= acquires > lock by default), which is IMO a breakage of backward compatibility. In the big software stack picture, it is okay to reject 'old libvirt/new qemu' as an invalid combination. Upgrade-wise, we specifically support 'new libvirt/old qemu' - but it is fair game to say that 'if you want to run new qemu, you must first upgrade to new libvirt that knows how to drive it'. That said, minimizing back-compat breaks, so that old libvirt can (usually) correctly drive new qemu, is a worthy design goal for qemu. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --wxl7vrNJWl08bq7UxAVFL8OgR0r3EEVC8 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 Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJWln7VAAoJEKeha0olJ0NqfycH/1U3m5CH5nSdlCvstcdS7Q2e 7WoucK68zzJve9uBxjY8Tq2BQrToTxMLoet3/oyKnPlp2D/VgzjTrPwTTQDPb3Nu vT+UvK9M57lYjIejio4Kp8mWPP5Kh00hmRcuYmerRtrHok7l7UTKBfYg2hLXdIIK drPpI6oGQ6IbQvUItd2MYCkaZnjD2Rg/5S0ql6L9Y5Nylx4CAkCqucGYqz54n0LN Ft9NTk28qSChidblkD0gvssTBbr5hdauCSVHldxft2+k1HS1IMlL9nSArjE1Ysj9 PCob8gwZWZcPp6rxt543D+DOxKzvk4NVa44xNAtriEEckGcUhgWtBH0okP0cptE= =LMr1 -----END PGP SIGNATURE----- --wxl7vrNJWl08bq7UxAVFL8OgR0r3EEVC8--