From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33166) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zgl7P-0005s9-W6 for qemu-devel@nongnu.org; Mon, 28 Sep 2015 22:58:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zgkxw-00046u-Si for qemu-devel@nongnu.org; Mon, 28 Sep 2015 22:48:32 -0400 References: <56094B0F.7030900@redhat.com> From: Eric Blake Message-ID: <5609FBE7.1070705@redhat.com> Date: Mon, 28 Sep 2015 20:48:07 -0600 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="R2MWIT8pbfdvO7TJ0torjXfuDADoBd2Ja" Subject: Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jeff Cody , Paolo Bonzini Cc: kwolf@redhat.com, jcody@redhat.com, stefanha@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --R2MWIT8pbfdvO7TJ0torjXfuDADoBd2Ja Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 09/28/2015 03:32 PM, Jeff Cody wrote: > I guess that makes sense. What about the case when the target is a ra= w > device without zero init? There is no backing file... Of course, perha= ps > in the raw case the user should be using sync=3D=3Dfull anyways. >=20 >> >> 2) even with mode =3D=3D "existing" you expect the data to be consiste= nt at >> the end of the mirroring >> >=20 > The reason I added the "existing" exception was so the user could avoid= the > time penalty of zeroing out the data if they knew the target had alread= y > explicitly been zeroed. Do you think it is fair to assume that if the = user > specified existing, that they take responsibility for setting up the ta= rget > image how they like (including data initialization)? Or should we add > another option for mirror, to allow the user to bypass the zero fill? mode =3D=3D 'existing' puts the burden on the caller to ensure that the f= ile they are passing in starts with known contents (either contents don't matter because we are doing sync =3D=3D 'full' to write every sector, or contents MUST initially match what the guest would see looking at the backing image when doing a shallow clone). But if there is a way for a user to pass in an existing file which they have pre-zeroed, even though the file would normally be treated as though it did not have zero fill, then the option to bypass a redundant zero fill might be useful. I'm not sure it's worth implementing without a known user, though, and I don't know that libvirt would use it. --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org --R2MWIT8pbfdvO7TJ0torjXfuDADoBd2Ja 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/ iQEcBAEBCAAGBQJWCfvnAAoJEKeha0olJ0NqrncIAIanem7hF2kli6BziwiH4PAB MTBJdWi9tyI51fYKxvacn1pRTLHTMCbZDDJj1xcF+CDv0LiQItVVgYoChYs9NCRb 0ocOEFafzttJN/jIb9CMJs2G0zS5sLb1S6Nh60EvoIaU4LdZRJU6FMJXqxzIlVKy Kxeq+BRNpvW7+tyy9hNQQsr9DOjjyJIkcwq7hweryYlf0CVI2Kp9u9wFtdsWaoDs E6Tqx4hZJR3aMfLSwvNYMtuWfwAKURQytZjCitvhNoTjNTPacxxSO32nt8gJn7cn NcA5aWJ5dK6Iw/2XHKbRyCCI65nQbB85ujJfsXxVZvh0YCV/nYjA1NdCMDNottE= =qth3 -----END PGP SIGNATURE----- --R2MWIT8pbfdvO7TJ0torjXfuDADoBd2Ja--