3484 enhance and document tail follow support
Reviewed by: Joshua M. Clulow <jmc@joyent.com>

*** 23,32 ****
--- 23,36 ----
   *
   *      Copyright (c) 1983,1984,1985,1986,1987,1988,1989 AT&T.
   *      All rights reserved.
   */
  
+ /*
+  * Copyright (c) 2013, Joyent, Inc. All rights reserved.
+  */
+ 
  #include <sys/param.h>
  #include <sys/types.h>
  #include <sys/systm.h>
  #include <sys/cred.h>
  #include <sys/time.h>
*** 2028,2048 ****
                          if (!(error = VOP_ACCESS(vp, mode, 0, cr, ct))) {
                                  if ((vattr.va_mask & AT_SIZE) &&
                                      vp->v_type == VREG) {
                                          vattr.va_mask = AT_SIZE;
                                          error = nfssetattr(vp, &vattr, 0, cr);
                                  }
                          }
                  }
                  nfs_rw_exit(&drp->r_rwlock);
                  if (error) {
                          VN_RELE(vp);
                  } else {
-                         /*
-                          * existing file got truncated, notify.
-                          */
-                         vnevent_create(vp, ct);
                          *vpp = vp;
                  }
                  return (error);
          }
  
--- 2032,2056 ----
                          if (!(error = VOP_ACCESS(vp, mode, 0, cr, ct))) {
                                  if ((vattr.va_mask & AT_SIZE) &&
                                      vp->v_type == VREG) {
                                          vattr.va_mask = AT_SIZE;
                                          error = nfssetattr(vp, &vattr, 0, cr);
+ 
+                                         if (!error) {
+                                                 /*
+                                                  * Existing file was truncated;
+                                                  * emit a create event.
+                                                  */
+                                                 vnevent_create(vp, ct);
                                          }
                                  }
                          }
+                 }
                  nfs_rw_exit(&drp->r_rwlock);
                  if (error) {
                          VN_RELE(vp);
                  } else {
                          *vpp = vp;
                  }
                  return (error);
          }