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Date: Mon, 30 May 2011 13:48:53 +0100 (BST)
From: Robert Watson <rwatson@FreeBSD.org>
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To: Rick Macklem <rmacklem@FreeBSD.org>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
	src-committers@freebsd.org
Subject: Re: svn commit: r222466 - head/sbin/umount
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On Sun, 29 May 2011, Rick Macklem wrote:

>  Modify the umount(8) command so that it doesn't do
>  a sync(2) syscall before unmount(2) for the "-f" case.
>  This avoids a forced dismount from getting stuck for
>  an NFS mountpoint in sync() when the server is not
>  responsive. With this commit, forced dismounts should
>  normally work for the NFS clients, but can take up to
>  about 1minute to complete.

I'm actually a bit confused about why umount(8) calls sync(2) at all: surely 
it's the responsibility of the file system, rather than the userland tool, to 
ensure consistency subject to file system configuration and unmount-time 
flags?

Robert