On Tue, Jul 20, 2010 at 11:12:17AM +0800, Ian Kent wrote:
> On Fri, 2010-07-16 at 17:02 -0400, Valerie Aurora wrote:
> > On Tue, Jul 13, 2010 at 12:47:02PM +0800, Ian Kent wrote:
> > > On Tue, Jun 15, 2010 at 11:39:51AM -0700, Valerie Aurora wrote:
> > > > +
> > > > +static int
> > > > +check_mnt_union(struct path *mntpnt, struct vfsmount *topmost_mnt, int mnt_flags)
> > > > +{
> > > > + struct vfsmount *lower_mnt = mntpnt->mnt;
> > > > +
> > > > + if (!(mnt_flags & MNT_UNION))
> > > > + return 0;
> > > > +
> > > > +#ifndef CONFIG_UNION_MOUNT
> > > > + return -EINVAL;
> > > > +#endif
> > > > + if (!(lower_mnt->mnt_sb->s_flags & MS_RDONLY))
> > > > + return -EBUSY;
> > > > +
> > > > + if (!list_empty(&lower_mnt->mnt_mounts))
> > > > + return -EBUSY;
> > > > +
> > > > + if (!IS_ROOT(mntpnt->dentry))
> > > > + return -EINVAL;
> > > > +
> > > > + if (mnt_flags & MNT_READONLY)
> > > > + return -EROFS;
> > > > +
> > > > + if (!(topmost_mnt->mnt_sb->s_flags & MS_WHITEOUT))
> > > > + return -EINVAL;
> > > > +
> > >
> > > Is there a need to check fallthru, umm ... that probably doesn't
> > > apply for the ROOT(), right?
> >
> > Actually, that's on my todo list - right now I'm assuming MS_WHITEOUT
> > implies fallthru support as well. But it doesn't.
> >
> > We're a little short on MS_* flags. I'm thinking of just checking
> > ->whiteout and ->fallthru for non-NULL on the root dir and getting rid
> > of MS_WHITEOUT entirely. Thoughts?
>
> Checking for the methods is a good idea I think, since they are assumed
> to be present by the code, at least in some places.
>
> Although it shouldn't happen, it is possible for a file system to create
> the root dentry with these methods defined but other dentrys without
> them defined, so a file system implementation error could cause some
> unpleasant crashes. Maybe requiring the flags to indicate support would
> help avoid unpleasant implementation problems like this, not sure
> really.
>
> Also not sure if a method existence check should always be made prior to
> use, regardless.
I went for MS_WHITEOUT and MS_FALLTHRU, and added the checks for the
ops being non-null.
-VAL
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