Date: Wed, 13 Nov 2002 03:14:03 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Terry Lambert <tlambert2@mindspring.com> Cc: "Daniel O'Connor" <doconnor@gsoft.com.au>, Hans Zaunere <zaunere@yahoo.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Shared files within a jail Message-ID: <200211131114.gADBE3lM069566@apollo.backplane.com> References: <20021113034726.75787.qmail@web12801.mail.yahoo.com> <1037159767.66058.34.camel@chowder.localdomain> <200211130530.gAD5UxNt067928@apollo.backplane.com> <3DD1FAB9.82607C41@mindspring.com>
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:> Try using null mounts. The warning is in there because making the
:> null mount code work is a real hack and the authors aren't entirely
:> sure that everything's gotten covered. That said, use of a null mount
:> is certainly a lot safer if the stuff behind the mount is mostly
:> static.
:
:The problem is in the VM object alias code. Specifically, the
:getpages/putpages have to be implemented in terms of read/write,
:so that there are not two vm_object_t's that refer to the same
:data, since there is no "upcall" to notify of changes in a lower
:layer, and therefore guarantee coherency.
I'm fairly sure the VM issues were fixed when VOP_GETVOBJECT was
added. A file accessed via a null mount will have the same VM object
as the file in the original filesystem. I'm not 100% sure about
that, I wasn't the one who did it, but I seem to recall it being
discussed.
-Matt
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