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Date: Wed, 22 Mar 2006 09:23:48 -0800 (PST)
From: Matthew Dillon <dillon@apollo.backplane.com>
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To: Kostik Belousov <kostikbel@gmail.com>
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Cc: alc@freebsd.org, Mikhail Teterin <mi+mx@aldan.algebra.com>,
	stable@freebsd.org
Subject: Re: more weird bugs with mmap-ing via NFS
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    My guess is that you are exporting the filesystem as a particular
    user id that is not root (i.e. you do not have -maproot=root: in the
    exports line on the server).

    What is likely happening is that the NFS client is trying to push out
    the pages using the root uid rather then the user uid.  This is a highly
    probable circumstance for VM pages because once they get disassociated
    from the related buffer cache buffer, the cred information for the
    last process to modify the related VM pages is lost.  When the kernel
    tries to flush the pages out it winds up using root creds.

    On DragonFly, I gave up entirely on trying to associate creds with
    buffers.

    I consider this more of a bug on the server side then on the client
    side.  The server should automatically translate the root uid to the
    exported uid for I/O ops.  Or, baring that, we have to add an option
    to the client-side mount to be able to specify a user/group id to 
    translate all I/O requests to.

						-Matt