NetBSD Problem Report #45711

From campbell@mumble.net  Tue Dec 13 22:58:05 2011
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Date: Tue, 13 Dec 2011 22:58:05 +0000 (UTC)
From: Taylor R Campbell <campbell+netbsd@mumble.net>
Reply-To: Taylor R Campbell <campbell+netbsd@mumble.net>
To: gnats-bugs@gnats.NetBSD.org
Subject: integrity properties of file systems are badly documented
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>Number:         45711
>Category:       kern
>Synopsis:       integrity properties of file systems are badly documented
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          doc-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 13 23:00:01 +0000 2011
>Originator:     Taylor R Campbell <campbell+netbsd@mumble.net>
>Release:        NetBSD 5.99.58
>Organization:
>Environment:
System: NetBSD oberon.local 5.99.58 NetBSD 5.99.58 (RIAMONOHACK) #4: Sat Dec 10 23:18:29 UTC 2011 root@oberon.local:/home/riastradh/netbsd/current/obj/sys/arch/i386/compile/RIAMONOHACK i386
Architecture: i386
Machine: i386
>Description:

	The assumptions made by our file systems and the intended
	integrity guarantees they are supposed to provide, particularly
	related to the meaning of fsck, `mount -o sync', and wapbl, are
	badly documented, and users are very confused about them.

>How-To-Repeat:

	Read tech-kern and try not to submerge in a sea of confusion.

>Fix:

	We ought to write down somewhere what assumptions the file
	systems make about the underlying disk devices, such as
	atomicity and ordering of disk sector writes and how those
	relate to disk write caches and power failures.

	We ought to clarify what integrity guarantees the file systems
	make, and how fsck/replay/&c. enforce those, and how fsck
	additionally sometimes works as a diagnostic or debugging tool
	when the assumptions may have broken down or bugs have
	manifested in the file systems.

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