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Date: Sat, 11 Oct 2008 08:54:44 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] Expand cache= option and use write-through
	caching by default
References: <1223671759-26576-1-git-send-email-aliguori@us.ibm.com>
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To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>, kvm@vger.kernel.org

Anthony Liguori wrote:
> This patch changes the cache= option to accept none, writeback, or writethough
> to control the host page cache behavior.  By default, writethrough caching is
> now used which internally is implemented by using O_DSYNC to open the disk
> images.  When using -snapshot, writeback is used by default since data integrity
> it not at all an issue.
>
> cache=none has the same behavior as cache=off previously.  The later syntax is
> still supported by now deprecated.  I also cleaned up the O_DIRECT
> implementation to avoid many of the #ifdefs.
>
>   

Looks good.

> @@ -8069,7 +8075,7 @@ static void help(int exitcode)
>             "-cdrom file     use 'file' as IDE cdrom image (cdrom is ide1 master)\n"
>  	   "-drive [file=file][,if=type][,bus=n][,unit=m][,media=d][,index=i]\n"
>             "       [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n"
> -           "       [,cache=on|off][,format=f]\n"
> +           "       [,cache=writethrough|writeback|none][,format=f]\n"
>  	   "                use 'file' as a drive image\n"
>             "-mtdblock file  use 'file' as on-board Flash memory image\n"
>             "-sd file        use 'file' as SecureDigital card image\n"
>
>   

Might want to specify the default, and also document it in the manual.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.