Re: [PATCH 06/15] NFSv4: Introduce new label structure

["Myklebust, Trond" <Trond.Myklebust@netapp.com>]

On Tue, 2013-02-12 at 17:32 -0500, J. Bruce Fields wrote:
> On Tue, Feb 12, 2013 at 10:28:16PM +0000, Myklebust, Trond wrote:
> > On Tue, 2013-02-12 at 17:07 -0500, J. Bruce Fields wrote:
> > > On Fri, Feb 08, 2013 at 07:39:14AM -0500, Steve Dickson wrote:
> > > > From: David Quigley <dpquigl@davequigley.com>
> > > > 
> > > > In order to mimic the way that NFSv4 ACLs are implemented we have created a
> > > > structure to be used to pass label data up and down the call chain. This patch
> > > > adds the new structure and new members to the required NFSv4 call structures.
> > > > 
> > > > Signed-off-by: Matthew N. Dodd <Matthew.Dodd@sparta.com>
> > > > Signed-off-by: Miguel Rodel Felipe <Rodel_FM@dsi.a-star.edu.sg>
> > > > Signed-off-by: Phua Eu Gene <PHUA_Eu_Gene@dsi.a-star.edu.sg>
> > > > Signed-off-by: Khin Mi Mi Aung <Mi_Mi_AUNG@dsi.a-star.edu.sg>
> > > > ---
> > > >  fs/nfs/inode.c            | 33 +++++++++++++++++++++++++++++++++
> > > >  include/linux/nfs4.h      |  7 +++++++
> > > >  include/linux/nfs_fs.h    | 17 +++++++++++++++++
> > > >  include/linux/nfs_xdr.h   | 21 +++++++++++++++++++++
> > > >  include/uapi/linux/nfs4.h |  2 +-
> > > >  5 files changed, 79 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
> > > > index ebeb94c..8d5f01b 100644
> > > > --- a/fs/nfs/inode.c
> > > > +++ b/fs/nfs/inode.c
> > > > @@ -255,6 +255,39 @@ nfs_init_locked(struct inode *inode, void *opaque)
> > > >  	return 0;
> > > >  }
> > > >  
> > > > +#ifdef CONFIG_NFS_V4_SECURITY_LABEL
> > > > +struct nfs4_label *nfs4_label_alloc(struct nfs_server *server, gfp_t flags)
> > > > +{
> > > > +	struct nfs4_label *label = NULL;
> > > > +
> > > > +	if (!(server->caps & NFS_CAP_SECURITY_LABEL))
> > > > +		return label;
> > > > +
> > > > +	label = kzalloc(NFS4_MAXLABELLEN, flags);
> > > > +	if (label == NULL)
> > > > +		return ERR_PTR(-ENOMEM);
> > > > +
> > > > +	label->label = (char *)(label + 1);
> > > > +	label->len = NFS4_MAXLABELLEN;
> > > 
> > > If you're expecting to be able to store up to NFS4_MAXLABELLEN of data
> > > after the end of the struct, then you want:
> > > 
> > > 	label = kzalloc(sizeof(struct nfs4_label) + NFS4_MAXLABELLEN, flags);
> > 
> > Sigh... No.
> > 
> > I keep telling Steve that the 'label' needs to be defined as an array,
> 
> Yeah, I know, he said in 0/15 that he couldn't do that, so I've been
> reading through these on the assumption I'll find out why not at some
> point....  (Still not seeing it, though.)

It only makes sense to define label->label as a pointer if you need to
change the pointer value at some time. However, if that is the case,
then why allocate the struct nfs4_label and label string as a single
memory block? It would make more sense to allocate them separately so
that you can free the old label storage after you change the pointer.

Trond