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To: John-Mark Gurney <jmg@funkthat.com>
cc: Aijaz Baig <aijazbaig1@gmail.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"
In-reply-to: <20170121235131.GF1768@funkthat.com>
From: "Poul-Henning Kamp" <phk@freebsd.org>
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Date: Sun, 22 Jan 2017 08:02:34 +0000
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--------
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 b=
lock
>> device' mean in this context? Was what I mentioned earlier with regards=
 to
>> my understanding correct? Viz. all disk devices now have a character (o=
r
>> 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 pass=
ing
>> 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
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Never attribute to malice what can adequately be explained by incompetence=
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