Re: MS_NOUSER and rootfs

[Andries Brouwer]

On Fri, Jan 07, 2005 at 01:53:32PM -0700, Thayne Harbaugh wrote:
> On Fri, 2005-01-07 at 19:32 +0200, Denis Vlasenko wrote:
> > On Thursday 06 January 2005 17:08, Thayne Harbaugh wrote:
> > > What is the purpose of the MS_NOUSER flag serve and why is it set on
> > > rootfs?

Some random docs say

The <tt>FS_NOMOUNT</tt> flag says that this filesystem must never
be mounted from userland, but is used only kernel-internally.
This flag was introduced in 2.3.99-pre7 and disappeared in Linux 2.5.22.
This was used, for example, for pipefs, the implementation of Unix pipes
using a kernel-internal filesystem (see <tt>fs/pipe.c</tt>).
Even though the flag has disappeared, the concept remains,
and is now represented by the MS_NOUSER flag.

> There isn't a description as to what the intention is for MS_NOUSER and
> why it should be applied to rootfs.  I'm looking for some education as
> to what it does so I can work out the details as to why it's used in
> graft_tree(), rootfs_get_sb() and shmem.c.
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