Date: Mon, 21 Nov 2011 15:00:30 GMT From: Gleb Kurtsou <gleb.kurtsou@gmail.com> To: freebsd-fs@FreeBSD.org Subject: Re: kern/162591: [nullfs] cross-filesystem nullfs does not work as expected Message-ID: <201111211500.pALF0UKv070180@freefall.freebsd.org>
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The following reply was made to PR kern/162591; it has been noted by GNATS. From: Gleb Kurtsou <gleb.kurtsou@gmail.com> To: bug-followup@FreeBSD.org, mw@wzff.de Cc: Subject: Re: kern/162591: [nullfs] cross-filesystem nullfs does not work as expected Date: Mon, 21 Nov 2011 16:23:47 +0200 That is expected behaviour, according to mount_nullfs(8): The mount_nullfs utility creates a null layer, duplicating a sub-tree of the file system name space under another part of the global file system namespace. It mentions sub-tree of a single file system only. nullfs is technically very different from loop mounts in Linux or nullfs in DragonFly, it doesn't map part of file name space elsewhere, but duplicates file system sub-tree. Messing with v_mountedhere in nullfs would bring much more trouble than it can potentially solve: VFS_VGET(), full path lookups, etc. We could add mount option to automatically nullfs-mount nested mounts, but it also feels overcomplicated: unmounting may be difficult, should we track new mounts, etc. Mounting nullfs over nullfs is a very bad idea imo (it it's not forbidden, I'd also suggest not to NFS export nullfs). I think writing a small script to do nested mounts/unmounts that suites your needs would be the best option here.
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