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	Mon, 20 Oct 1997 05:55:35 -0500 (EST)
From: "John S. Dyson" <toor@dyson.iquest.net>
Message-Id: <199710201055.FAA01099@dyson.iquest.net>
Subject: Re: nullfs & current
In-Reply-To: <406.877333677@critter.freebsd.dk> from Poul-Henning Kamp at "Oct 20, 97 09:47:57 am"
To: phk@critter.freebsd.dk (Poul-Henning Kamp)
Date: Mon, 20 Oct 1997 05:55:35 -0500 (EST)
Cc: toor@dyson.iquest.net, roberto@keltia.freenix.fr, current@FreeBSD.ORG
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Poul-Henning Kamp said:
> In message <199710200143.UAA05747@dyson.iquest.net>, "John S. Dyson" writes:
> >Ollivier Robert said:
> >> According to John S. Dyson:
> >> > The VM system holds a reference.  You have to do a vnode_pager_uncache whe
> >n
> >> > deleting a file.
> >> 
> >> Wait... Isn't ufs_remove() supposed to do that ? ufs_remove() is called by
> >> null_bypass() by an indirect call (VCALL()) and it seemed safe to consider
> >> that the lower level was supposed to DTR.
> >> 
> >> Do I have to create a null_remove() function in order to call
> >> vnode_pager_uncache inside it ?
> >> 
> >nullfs should really share the VM object with the lower filesystem, but genera
> >lly
> >what you say is true, even if you don't share the object.  The complexity is
> >one reason that I haven't fixed it.  It IS fixable reasonably though.
> 
> No, this is wrong.  Nullfs can only share the VM object if the
> permissions are the same, consider a read-only mounted nullfs for
> instance.
> 
The VM object should be shared to maintain coherency.  Permissions
are maintained by the VM_MAP layer.  Objects are mosly globs of data.
For some apps, an object can be RO, and others RW.

-- 
John
dyson@freebsd.org
jdyson@nc.com