From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51456) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dxFDV-0008Uy-Tx for qemu-devel@nongnu.org; Wed, 27 Sep 2017 12:29:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dxFDV-000625-26 for qemu-devel@nongnu.org; Wed, 27 Sep 2017 12:29:45 -0400 References: <20170926175942.GE14717@localhost.localdomain> From: Max Reitz Message-ID: Date: Wed, 27 Sep 2017 18:29:33 +0200 MIME-Version: 1.0 In-Reply-To: <20170926175942.GE14717@localhost.localdomain> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="HxlUI1j4tWXKA68Gn3xup8fUDf901WDVV" Subject: Re: [Qemu-devel] blockdev-commit design List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, eblake@redhat.com, stefanha@redhat.com, jcody@redhat.com This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --HxlUI1j4tWXKA68Gn3xup8fUDf901WDVV From: Max Reitz To: Kevin Wolf , qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, eblake@redhat.com, stefanha@redhat.com, jcody@redhat.com Message-ID: Subject: Re: blockdev-commit design References: <20170926175942.GE14717@localhost.localdomain> In-Reply-To: <20170926175942.GE14717@localhost.localdomain> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 2017-09-26 19:59, Kevin Wolf wrote: [...] > * The old block-commit command decides between an "actual" commit job= > and the mirror-based active commit based on whether top is the > active layer. >=20 > We don't get an option for the active layer any more now, so this > isn't how things can work for blockdev-commit. We could probably > check whether top has a BlockBackend parent, but that's not really > what we're interested in anyway. Maybe the best we could do to > decide this automatically is to check whether there is any parent o= f > top that requires write permissions. If there is, we need active > commit, otherwise the "normal" one is good enough. >=20 > However, who says that the intentions of the user stay as we deduce= > them at the start of the block job? Who says that the user doesn't > want to add a writable disk as a user of the node while the block > job is running? >=20 > The optimal solution to this would be that the commit filter node > responds to permission requests and switches between active and > "normal" commit mode. I'm not sure how hard this would be to > implement. >=20 > As long as we don't have the automatic switch, do we have to allow > the user to specify explicitly which mode they want instead of > automatically choosing one? Probably a stupid question: What advantage does the commit job have over the mirror job? I.e. would it be possible to just always do a mirror? Max --HxlUI1j4tWXKA68Gn3xup8fUDf901WDVV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQFGBAEBCAAwFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAlnL0e0SHG1yZWl0ekBy ZWRoYXQuY29tAAoJEPQH2wBh1c9A2hYH/17Suss87xN6J/8//NfJJyCKzLC/g66S AcmNNwhCi6CV/SRUi4J1sEvWHpFHfr8N3jCJOMIlTKqtQNYWwBZ6xpCirG06W3ic w8mHXvtdBcmoY4UUHbvtGAuB00dWNFTYN4oJCY34r8q+WR7PeT6Iiqw9DjRpCn0x /Cepsw0447xj1llLGwdFWp3ZfEJXlsj2xvV4VUO4JOh0KQckC132gi/pDMEKijdc wfL3LaFtMOXZFVBjmthSrzIs3wjRsH2jOhDUBkxzxY2Idc8nWTSSDudjXfTwvZi5 6TfudZgW4cMzVHnhtbtSvPtDwzQOXNhpCQ8ryTcGKBCAjyE+XahGEx4= =v6rl -----END PGP SIGNATURE----- --HxlUI1j4tWXKA68Gn3xup8fUDf901WDVV--