Date: Tue, 8 Dec 2015 13:20:28 -0700 From: Warner Losh <imp@bsdimp.com> To: =?UTF-8?Q?Dag=2DErling_Sm=C3=B8rgrav?= <des@des.no> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Steven Hartland <killing@multiplay.co.uk> Subject: Re: DELETE support in the VOP_STRATEGY(9)? Message-ID: <CANCZdfoc=tkf3qg%2BKYA3eoeovP0XvCa1BkHNNDrk9mDmoS7Jpg@mail.gmail.com> In-Reply-To: <86wpsopulm.fsf@desk.des.no> References: <CAH7qZftSVAYPmxNCQy=VVRj79AW7z9ade-0iogv2COfo2x%2Ba2Q@mail.gmail.com> <201512052002.tB5K2ZEA026540@chez.mckusick.com> <CAH7qZfs6ksE%2BQTMFFLYxY0PNE4hzn=D5skzQ91=gGK2xvndkfw@mail.gmail.com> <86poyhqsdh.fsf@desk.des.no> <CAH7qZftVj9m_yob=AbAQA7fh8yG-VLgM7H0skW3eX_S%2Bv75E-g@mail.gmail.com> <86fuzdqjwn.fsf@desk.des.no> <CANCZdfo=NfKy51%2B64-F_v%2BDh2wkrFYP4gXe=X9RWSSao49gO9g@mail.gmail.com> <CANCZdfqHoduhdCss0b6=UsBPAxfRZv4hF8vyuUVLBdP5gYUduQ@mail.gmail.com> <864mfssxgt.fsf@desk.des.no> <CANCZdfoXdcD%2B9jeVR1Np16gafBf0_4B2wombwxze8DvJwf7cMg@mail.gmail.com> <86wpsord9l.fsf@desk.des.no> <566726ED.2010709@multiplay.co.uk> <0DB97CBA-4DC3-4D52-AE9D-54546292D66F@bsdimp.com> <86d1ugrb7j.fsf@desk.des.no> <CANCZdfrgkA-znp8jL%2BfDgkXwaTSBeNJVTXj6mDKQxdYtht3uzA@mail.gmail.com> <868u54radx.fsf@desk.des.no> <E7F0EECA-724C-4595-AB4A-96E29EF6871B@bsdimp.com> <86wpsopulm.fsf@desk.des.no>
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On Tue, Dec 8, 2015 at 1:13 PM, Dag-Erling Sm=C3=B8rgrav <des@des.no> wrote= : > Warner Losh <imp@bsdimp.com> writes: > > And to be fair, having an additional property of =E2=80=98seeks are nea= rly > > free=E2=80=99 would also be a good way to tell. I=E2=80=99m not convinc= ed it is worth > > the effort to add it to all the storage devices in the tree when > > GEOM::candelete is a good proxy. > > I just provided you with an (admittedly fictional, but not unreasonable) > example of a layer which implements BIO_DELETE on top of storage that > may or may not have free seeks. The two are completely orthogonal; they > just happen to be strongly correlated on currently available hardware. > > Note that my fictional example would guarantee that BIO_DELETEd space > reads back as zeroes, even if the request doesn't align with physical > block boundaries. Sounds pretty useful to me, even if it doesn't > guarantee that the deleted data cannot be recovered from the physical > media by a sufficiently determined attacker with access to liquid > nitrogen and an electron microscope. And when there's an actual example, I'm happy to re-examine the use of GEOM::candelete. Warner
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