libdiskfs: lock-less reference counting for peropen objects

* libdiskfs/diskfs.h (struct peropen): Use refcount_t for field refcnt.
* libdiskfs/peropen-make.c (diskfs_make_peropen): Initialize refcnt.
* libdiskfs/peropen-rele.c (diskfs_release_peropen): Adjust accordingly.
* libdiskfs/protid-make.c (diskfs_start_protid): Likewise.  Also, the
node must no longer be locked, adjust comment accordingly.
(diskfs_create_protid): Likewise.

4 files changed, 19 insertions, 19 deletions

diff --git a/libdiskfs/diskfs.h b/libdiskfs/diskfs.h
index 8151ddc1..ae1a1502 100644
--- a/libdiskfs/diskfs.h
+++ b/libdiskfs/diskfs.h
@@ -28,6 +28,7 @@
 #include <hurd/iohelp.h>
 #include <idvec.h>
 #include <features.h>
+#include <refcount.h>
 
 #ifdef DISKFS_DEFINE_EXTERN_INLINE
 #define DISKFS_EXTERN_INLINE
@@ -57,7 +58,7 @@ struct peropen
 {
   int filepointer;
   int lock_status;
-  int refcnt;
+  refcount_t refcnt;
   int openstat;
 
   struct node *np;
@@ -792,12 +793,12 @@ diskfs_create_node (struct node *dir, const char *name, mode_t mode,
 		    struct dirstat *ds);
 
 /* Create and return a protid for an existing peropen PO in CRED,
-   referring to user USER.  The node PO->np must be locked. */
+   referring to user USER.  */
 error_t diskfs_create_protid (struct peropen *po, struct iouser *user,
 			      struct protid **cred);
 
 /* Build and return in CRED a protid which has no user identification, for
-   peropen PO.  The node PO->np must be locked.  */
+   peropen PO.  */
 error_t diskfs_start_protid (struct peropen *po, struct protid **cred);
 
 /* Finish building protid CRED started with diskfs_start_protid;
diff --git a/libdiskfs/peropen-make.c b/libdiskfs/peropen-make.c
index eba037ff..6d5ca014 100644
--- a/libdiskfs/peropen-make.c
+++ b/libdiskfs/peropen-make.c
@@ -31,7 +31,7 @@ diskfs_make_peropen (struct node *np, int flags, struct peropen *context,
 
   po->filepointer = 0;
   po->lock_status = LOCK_UN;
-  po->refcnt = 0;
+  refcount_init (&po->refcnt, 0);
   po->openstat = flags;
   po->np = np;
   po->path = NULL;
diff --git a/libdiskfs/peropen-rele.c b/libdiskfs/peropen-rele.c
index d3f74921..877137bb 100644
--- a/libdiskfs/peropen-rele.c
+++ b/libdiskfs/peropen-rele.c
@@ -22,13 +22,8 @@
 void
 diskfs_release_peropen (struct peropen *po)
 {
-  pthread_mutex_lock (&po->np->lock);
-
-  if (--po->refcnt)
-    {
-      pthread_mutex_unlock (&po->np->lock);
-      return;
-    }
+  if (refcount_deref (&po->refcnt) > 0)
+    return;
 
   if (po->root_parent)
     mach_port_deallocate (mach_task_self (), po->root_parent);
@@ -40,10 +35,14 @@ diskfs_release_peropen (struct peropen *po)
     mach_port_deallocate (mach_task_self (), po->shadow_root_parent);
 
   if (po->lock_status != LOCK_UN)
-    fshelp_acquire_lock (&po->np->userlock, &po->lock_status,
-			 &po->np->lock, LOCK_UN);
-
-  diskfs_nput (po->np);
+    {
+      pthread_mutex_lock (&po->np->lock);
+      fshelp_acquire_lock (&po->np->userlock, &po->lock_status,
+                           &po->np->lock, LOCK_UN);
+      diskfs_nput (po->np);
+    }
+  else
+    diskfs_nrele (po->np);
 
   free (po->path);
   free (po);
diff --git a/libdiskfs/protid-make.c b/libdiskfs/protid-make.c
index b39b92af..22aaa2e1 100644
--- a/libdiskfs/protid-make.c
+++ b/libdiskfs/protid-make.c
@@ -20,7 +20,7 @@
 #include <assert.h>
 
 /* Build and return in CRED a protid which has no user identification, for
-   peropen PO.  The node PO->np must be locked.  */
+   peropen PO.  */
 error_t
 diskfs_start_protid (struct peropen *po, struct protid **cred)
 {
@@ -29,7 +29,7 @@ diskfs_start_protid (struct peropen *po, struct protid **cred)
 				 sizeof (struct protid), cred);
   if (! err)
     {
-      po->refcnt++;
+      refcount_ref (&po->refcnt);
       (*cred)->po = po;
       (*cred)->shared_object = MACH_PORT_NULL;
       (*cred)->mapped = 0;
@@ -55,8 +55,8 @@ diskfs_finish_protid (struct protid *cred, struct iouser *user)
   assert_perror (err);
 }
 
-/* Create and return a protid for an existing peropen PO in CRED for USER.
-   The node PO->np must be locked. */
+/* Create and return a protid for an existing peropen PO in CRED for
+   USER.  */
 error_t
 diskfs_create_protid (struct peropen *po, struct iouser *user,
 		      struct protid **cred)