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Date: Sat, 20 Feb 2016 13:49:20 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Stefan Esser <se@freebsd.org>
Cc: Eric van Gyzen <vangyzen@FreeBSD.org>,
 Bryan Drewery <bdrewery@FreeBSD.org>, src-committers@freebsd.org,
 svn-src-all@freebsd.org, svn-src-head@freebsd.org, dwmalone@FreeBSD.org
Subject: Re: svn commit: r295800 - head/usr.bin/cap_mkdb
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On Sat, Feb 20, 2016 at 10:37:17AM +0100, Stefan Esser wrote:
> I had assumed that one of the guarantees soft-updates makes is that
> data and meta-data operations are ordered relative to each other.

This is not true, SU never provided such guarantee. SU only ensures
the correctness of the metadata for any moment in time, or innocent
inconsistencies, where operation cannot be made atomic and consistent
simultaneously.

In other words, in this case, SU guarantees that the data blocks which
are allocated for writes, are not used by other inode, as recorded by
the metadata on disk, _if_ blocks are recorded in the on-disk inode. It
makes absolutely no guarantees about the flushing of the data buffers.