From owner-freebsd-hackers@freebsd.org Tue Jan 24 04:40:17 2017 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 7DCDACBF0A3; Tue, 24 Jan 2017 04:40:17 +0000 (UTC) (envelope-from aijazbaig1@gmail.com) Received: from mail-wm0-x235.google.com (mail-wm0-x235.google.com [IPv6:2a00:1450:400c:c09::235]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 154AA3EC; Tue, 24 Jan 2017 04:40:17 +0000 (UTC) (envelope-from aijazbaig1@gmail.com) Received: by mail-wm0-x235.google.com with SMTP id r126so163416730wmr.0; Mon, 23 Jan 2017 20:40:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=6TVJwf6yjP1d56UpF8cXGajYWsnDZcxv0oePv8iA1Oc=; b=Yy9EgPKSO0EVxcKnrN/1odQq0EgPlTDJHP7tvLXyL6p9azpJyM7ZrK3NIY7mue3+B4 5GCfPB8DDCgFkzDbMZLV3wIEsuK4HiEiOwHatti0ic9U5yNCPS88cLU6zRfT3po9gszW BqH7n3UjKlwQSGDHgb9bxmnBNbDRky8WmoIylG97hCEzXXd0MUbGa5noudbSUzaVs71x EY49i8Ap9FWwuBX6WMua4D324bnvdee+/3TCkIWgwtM5hR8oGwfpnyrXpqvubvxO6GBJ MAt8zVCmYVYuoF+hfhSdueZhWX6XaRLo4wSQpe1JsjkVstyltumj6oIvnkz+Ua7ctkKW qaOw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=6TVJwf6yjP1d56UpF8cXGajYWsnDZcxv0oePv8iA1Oc=; b=r4xsFhSivGLEHylJ2g1xe+bSeZtNpp8Kht5H93mz5wlGJj1yJ6y0xVMzdQLPkVTrIG +Toom0fDKbAkXSbwGRLu0s4BOkKCq+LGUPGFqrR/8wRjn9v/A1qHsuFLkFY+7ZNjgITf RdJtGPxK6db+tE0b2YO9Uv/9ILbTC0XVBI4i8vDMJwkY7S0ymPGP5rbjtPjyPFBubzaw hXSB8XptFwh0EIXs8RdAwbhwaFbv/6LFp9AhKxIG1tbZeiSssJSONavjpykGl/LEoesa jrbBqlelwgqF+4bbYehluFfThDFYTrhpGYS8VesO+AnHeNF6PA4kTDjDudxSIIYtgCAq +Qgg== X-Gm-Message-State: AIkVDXKqcAv6/Ns4U32KVv6qTMbK6xjeEbpyuIt/uVnhMu/Yfrh8KmEqjgUlJMUy8fN33y61TCLZgIe3JHqBPA== X-Received: by 10.223.165.87 with SMTP id j23mr32293490wrb.79.1485232815040; Mon, 23 Jan 2017 20:40:15 -0800 (PST) MIME-Version: 1.0 Received: by 10.194.189.103 with HTTP; Mon, 23 Jan 2017 20:40:14 -0800 (PST) In-Reply-To: <74696.1485072154@critter.freebsd.dk> References: <20170116071105.GB4560@eureka.lemis.com> <20170121235131.GF1768@funkthat.com> <74696.1485072154@critter.freebsd.dk> From: Aijaz Baig Date: Tue, 24 Jan 2017 10:10:14 +0530 Message-ID: Subject: Re: Understanding the rationale behind dropping of "block devices" To: Poul-Henning Kamp Cc: John-Mark Gurney , "Greg 'groggy' Lehey" , FreeBSD Hackers , freebsd-scsi@freebsd.org Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 Jan 2017 04:40:17 -0000 Oh thank you Poul. This would hopefully cover almost everything I need to know! On Sun, Jan 22, 2017 at 1:32 PM, Poul-Henning Kamp wrote: > -------- > In message <20170121235131.GF1768@funkthat.com>, John-Mark Gurney writes: > >Aijaz Baig wrote this message on Mon, Jan 16, 2017 at 14:19 +0530: > >> Nevertheless my question still holds. What does 'removing support for > block > >> device' mean in this context? Was what I mentioned earlier with regards > to > >> my understanding correct? Viz. all disk devices now have a character (or > >> raw) interface and are no longer served via the "page cache" but rather > the > >> "buffer cache". Does that mean all disk accesses are now direct by > passing > >> the file system?? > > > >One of the other reasons block devices were removed was that if there > >was a write error on the underlying device, there was no way for the > >writer to know that the write failed. This could/would lead to corrupted > >data which is bad. > > This paper hopefully answers a lot of the questions: > > https://www.usenix.org/conference/bsdcon02/rethinking-dev-and-devices- > unix-kernel > > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > -- Best Regards, Aijaz Baig