pnfs: change layout state seqlock to a spinlock

This prepares for future changes, where the layout state needs
to change atomically with several other variables.  In particular,
it will need to know if lo->segs is empty, as we test that instead
of manipulating the NFS_LAYOUT_STATEID_SET bit.  Moreover, the
layoutstateid is not really a read-mostly structure, as it is
written almost as often as it is read.

The behavior of pnfs_get_layout_stateid is also slightly changed, so that
it no longer changes the stateid.  Its name is changed to +pnfs_choose_layoutget_stateid.

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 3 insertions, 4 deletions

diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index c2f108640fc4..10937203d236 100644
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -44,7 +44,6 @@ struct pnfs_layout_segment {
 enum {
         NFS_LAYOUT_RO_FAILED = 0,       /* get ro layout failed stop trying */
         NFS_LAYOUT_RW_FAILED,           /* get rw layout failed stop trying */
-        NFS_LAYOUT_STATEID_SET,         /* have a valid layout stateid */
 };
 
 /* Per-layout driver specific registration structure */
@@ -63,7 +62,6 @@ struct pnfs_layout_hdr {
         unsigned long           plh_refcount;
         struct list_head        plh_layouts;   /* other client layouts */
         struct list_head        plh_segs;      /* layout segments list */
-        seqlock_t               plh_seqlock;   /* Protects the stateid */
         nfs4_stateid            plh_stateid;
         unsigned long           plh_flags;
         struct inode            *plh_inode;
@@ -143,8 +141,9 @@ int pnfs_layout_process(struct nfs4_layoutget *lgp);
 void pnfs_destroy_layout(struct nfs_inode *);
 void pnfs_destroy_all_layouts(struct nfs_client *);
 void put_layout_hdr(struct inode *inode);
-void pnfs_get_layout_stateid(nfs4_stateid *dst, struct pnfs_layout_hdr *lo,
-                             struct nfs4_state *open_state);
+int pnfs_choose_layoutget_stateid(nfs4_stateid *dst,
+                                  struct pnfs_layout_hdr *lo,
+                                  struct nfs4_state *open_state);
 
 
 static inline int lo_fail_bit(u32 iomode)