Date: Tue, 24 Jan 2017 10:10:14 +0530 From: Aijaz Baig <aijazbaig1@gmail.com> To: Poul-Henning Kamp <phk@freebsd.org> Cc: John-Mark Gurney <jmg@funkthat.com>, "Greg 'groggy' Lehey" <grog@freebsd.org>, FreeBSD Hackers <freebsd-hackers@freebsd.org>, freebsd-scsi@freebsd.org Subject: Re: Understanding the rationale behind dropping of "block devices" Message-ID: <CAHB2L%2BfPpqCZJ_PXfgxZDS2qDAvs5M9fLRMXWg1d%2B4eDgqxQ9w@mail.gmail.com> In-Reply-To: <74696.1485072154@critter.freebsd.dk> References: <CAHB2L%2BdRbX=E9NxGLd_eHsEeD0ZVYDYAx2k9h17BR0Lc=xu5HA@mail.gmail.com> <20170116071105.GB4560@eureka.lemis.com> <CAHB2L%2Bd9=rBBo48qR%2BPXgy%2BJDa=VRk5cM%2B9hAKDCPW%2BrqFgZAQ@mail.gmail.com> <20170121235131.GF1768@funkthat.com> <74696.1485072154@critter.freebsd.dk>
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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 <phk@freebsd.org> 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
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