From mboxrd@z Thu Jan 1 00:00:00 1970 From: Doug Ledford Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Date: Wed, 06 Feb 2019 16:12:06 -0500 Message-ID: References: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> <20190206095000.GA12006@quack2.suse.cz> <20190206173114.GB12227@ziepe.ca> <20190206175233.GN21860@bombadil.infradead.org> <47820c4d696aee41225854071ec73373a273fd4a.camel@redhat.com> <20190206183503.GO21860@bombadil.infradead.org> <20190206185233.GE12227@ziepe.ca> <671e7ebc8e125d1ebd71de9943868183e27f052b.camel@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-Wt2EcFKp3kDyEr43gL+b" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Dan Williams Cc: Jason Gunthorpe , Matthew Wilcox , Jan Kara , Ira Weiny , lsf-pc@lists.linux-foundation.org, linux-rdma , Linux MM , Linux Kernel Mailing List , John Hubbard , Jerome Glisse , Dave Chinner , Michal Hocko List-Id: linux-rdma@vger.kernel.org --=-Wt2EcFKp3kDyEr43gL+b Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2019-02-06 at 13:04 -0800, Dan Williams wrote: > On Wed, Feb 6, 2019 at 12:14 PM Doug Ledford wrote: > > On Wed, 2019-02-06 at 11:45 -0800, Dan Williams wrote: > > > On Wed, Feb 6, 2019 at 10:52 AM Jason Gunthorpe wrote: > > > > On Wed, Feb 06, 2019 at 10:35:04AM -0800, Matthew Wilcox wrote: > > > >=20 > > > > > > Admittedly, I'm coming in late to this conversation, but did I = miss the > > > > > > portion where that alternative was ruled out? > > > > >=20 > > > > > That's my preferred option too, but the preponderance of opinion = leans > > > > > towards "We can't give people a way to make files un-truncatable"= . > > > >=20 > > > > I haven't heard an explanation why blocking ftruncate is worse than > > > > giving people a way to break RDMA using process by calling ftruncat= e?? > > > >=20 > > > > Isn't it exactly the same argument the other way? > > >=20 > > > If the > > > RDMA application doesn't want it to happen, arrange for it by > > > permissions or other coordination to prevent truncation, > >=20 > > I just argued the *exact* same thing, except from the other side: if yo= u > > want a guaranteed ability to truncate, then arrange the perms so the > > RDMA or DAX capable things can't use the file. >=20 > That doesn't make sense. All we have to work with is rwx bits. It's > possible to prevents writes / truncates. There's no permission bit for > mmap, O_DIRECT and RDMA mappings, hence leases. There's ownership. What you can't open, you can't mmap or O_DIRECT or whatever... Regardless though, this is mostly moot as Dave's email makes it clear the underlying issue that is the problem is not ftruncate, but other things. > >=20 --=20 Doug Ledford GPG KeyID: B826A3330E572FDD Key fingerprint =3D AE6B 1BDA 122B 23B4 265B 1274 B826 A333 0E57 2FDD --=-Wt2EcFKp3kDyEr43gL+b Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEErmsb2hIrI7QmWxJ0uCajMw5XL90FAlxbTaYACgkQuCajMw5X L91UVRAAxQypVAaB7i52h2wDJpx5+mYhH6IiQWrtqd8xa0l2UZ2VHrRkdsn4wzGt BQFhIJZKPh3b7yzsYKzhe9HicMCXRIXPKw/KmgJLDcDmi1hU1QCMHKohniWUbJ6G g0IfJrLoPmMhNKn0Cm7J4s5jsP2QW6/CUn6/CGOQhWG1GtcuyFL6fCl5Bn0FFn9s cfKDGgJ9Wy4wiguackEO+W6XUN9YFz9P4K9HMqVwXfHXXiZR2Z9H6xHQOZkafylA KhjP2h8o0Jip4HDKOMJoP9AbmFFXK3ualefeiDoginb6D7tVs0/sbyImBTfTLzbt 7GBSNa/9Ue8qi7ZU6/ppjQILfn0mbnxV0JRV/nBOXfLeZeO1mbD2EDuPSOL+kXX4 Z4uvFWA7UxIkBTh4lwQY8g9uan3578jtdF4SNe//GBAA+pPTV9oXzzbTX+UXYE/U MmmQjk2S+ax7PINhTZhBbkGWqVLG95Pb3UtmxPSG1uFlxdkv/DSJqkm9qeNuHZu5 Tf1Zxl648P1g7Jk6c+1hlqpe/Rt7vsjU/1gQKYMyR4ViBrvlyiwkEokrqHdN2wnK YaJ8HcFQazJK8BwNFYmbMgWpvBN107gSh3yd3jnRm0PyxcWXNW+OfQ4X6xrgaLTQ m6lMl9vg0O/rHaf7P53MHmweNKEOLTcH7jp1/BQ1AM5zHMN5QOA= =Ct0f -----END PGP SIGNATURE----- --=-Wt2EcFKp3kDyEr43gL+b--