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From: ebiederm@xmission.com (Eric W. Biederman)
To: "Serge E. Hallyn" <serue@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, Kirill Korotaev <dev@openvz.org>,
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       Dave Hansen <haveblue@us.ibm.com>
Subject: Re: [PATCH -mm 5/7] add user namespace
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Date: Thu, 13 Jul 2006 21:50:17 -0600
In-Reply-To: <20060713212218.GA2169@sergelap.austin.ibm.com> (Serge
	E. Hallyn's message of "Thu, 13 Jul 2006 16:22:18 -0500")
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"Serge E. Hallyn" <serue@us.ibm.com> writes:

> Quoting Eric W. Biederman (ebiederm@xmission.com):
>> >> keys are essentially security credentials for something besides the
>> >> local kernel.  Think kerberos tickets.  That makes the keys the
>> >> obvious place to say what uid you are in a different user namespace
>> >> and similar things.
>> >
>> > what about performance ? wouldn't that slow the checking ?
>> 
>> It needs to be looked at, but it shouldn't slow the same namespace
>> case,
>
> How so?  The processesing is the same.

If you do mapping of uids that would not trigger if you have
matching user namespaces.

>> and permission checking is largely a slow path issue.  So a little
>> overhead at open time is preferred to overhead after you get the file
>> open.
>
> Unsure which approach has overhead after file open...

I don't know that I have seen that one yet.  Sorry this was generally
a statement of principle.

Eric