Date: Sat, 2 Mar 2013 01:00:33 +0100 From: Jilles Tjoelker <jilles@stack.nl> To: Konstantin Belousov <kostikbel@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: [patch] statfs does not detect -t nullfs -o union as a union mount Message-ID: <20130302000032.GB49921@stack.nl> In-Reply-To: <20130227222144.GG2454@kib.kiev.ua> References: <20130227213141.GA18210@stack.nl> <20130227222144.GG2454@kib.kiev.ua>
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On Thu, Feb 28, 2013 at 12:21:44AM +0200, Konstantin Belousov wrote:
> On Wed, Feb 27, 2013 at 10:31:42PM +0100, Jilles Tjoelker wrote:
> > While testing recent changes to opendir(), I noticed that fstatfs() does
> > not return the MNT_UNION flag for a -t nullfs -o union mount. As a
> > result, opendir()/readdir() return files that exist in both top and
> > bottom directories twice (at least . and ..). Other -o union mounts and
> > -t unionfs mounts work correctly in this regard.
> > The below patch passes through just the MNT_UNION flag of the nullfs
> > mount itself. Perhaps more flags should be passed through.
> > commit fce32a779af4eb977c9b96feb6e4f811d89f2881
> > Author: Jilles Tjoelker <jilles@stack.nl>
> > Date: Sat Feb 23 22:22:39 2013 +0100
> >
> > nullfs: Preserve the MNT_UNION flag of the nullfs mount itself.
> >
> > This is needed so that opendir() can properly detect a union mount like
> > mount -t nullfs -o union dir1 dir2.
> >
> > diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
> > index 3724e0a..ff06f57 100644
> > --- a/sys/fs/nullfs/null_vfsops.c
> > +++ b/sys/fs/nullfs/null_vfsops.c
> > @@ -313,7 +313,7 @@ nullfs_statfs(mp, sbp)
> >
> > /* now copy across the "interesting" information and fake the rest */
> > sbp->f_type = mstat.f_type;
> > - sbp->f_flags = mstat.f_flags;
> > + sbp->f_flags = (sbp->f_flags & MNT_UNION) | mstat.f_flags;
> > sbp->f_bsize = mstat.f_bsize;
> > sbp->f_iosize = mstat.f_iosize;
> > sbp->f_blocks = mstat.f_blocks;
> Would it make sense to preserve more flags from the upper mount ?
> I see a use for MNT_NOEXEC as well, at least.
Yes, preserving MNT_NOEXEC will make -t nullfs -o noexec work better, in
particular rtld's check for libraries loaded via environment variables.
In the same way MNT_RDONLY, MNT_NOSUID and MNT_NOSYMFOLLOW could be
preserved.
On the other hand, MNT_ROOTFS should probably not be passed through from
the underlying filesystem.
This would give
sbp->f_flags = (sbp->f_flags & (MNT_RDONLY | MNT_NOEXEC | MNT_NOSUID |
MNT_UNION | MNT_NOSYMFOLLOW) | (mstat.f_flags & ~MNT_ROOTFS);
--
Jilles Tjoelker
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