diff --git a/ompi/mca/fbtl/posix/fbtl_posix.c b/ompi/mca/fbtl/posix/fbtl_posix.c
index 29dbdb4197..65f01c20d6 100644
--- a/ompi/mca/fbtl/posix/fbtl_posix.c
+++ b/ompi/mca/fbtl/posix/fbtl_posix.c
@@ -203,6 +203,7 @@ bool mca_fbtl_posix_progress ( mca_ompio_request_t *req)
 	/* all pending operations are finished for this request */
 	req->req_ompi.req_status.MPI_ERROR = OMPI_SUCCESS;
 	req->req_ompi.req_status._ucount = data->aio_total_len;
+        mca_fbtl_posix_unlock ( &data->aio_lock, data->aio_fh );
 	ret = true;
     }
 #endif
@@ -215,6 +216,7 @@ void mca_fbtl_posix_request_free ( mca_ompio_request_t *req)
     /* Free the fbtl specific data structures */
     mca_fbtl_posix_request_data_t *data=(mca_fbtl_posix_request_data_t *)req->req_data;
     if (NULL != data ) {
+        mca_fbtl_posix_unlock ( &data->aio_lock, data->aio_fh );
 	if ( NULL != data->aio_reqs ) {
 	    free ( data->aio_reqs);
 	}
diff --git a/ompi/mca/fbtl/posix/fbtl_posix_lock.c b/ompi/mca/fbtl/posix/fbtl_posix_lock.c
index 30551b4424..31897d5c91 100644
--- a/ompi/mca/fbtl/posix/fbtl_posix_lock.c
+++ b/ompi/mca/fbtl/posix/fbtl_posix_lock.c
@@ -43,6 +43,9 @@ int mca_fbtl_posix_lock ( struct flock *lock, mca_io_ompio_file_t *fh, int op,
     lock->l_whence = SEEK_SET;
     lock->l_start  =-1;
     lock->l_len    =-1;
+    if ( 0 == len ) {
+        return 0;
+    } 
     if ( fh->f_atomicity ||
          fh->f_flags & OMPIO_LOCK_ALWAYS ) {
         /* Need to lock the entire region */
@@ -66,7 +69,7 @@ int mca_fbtl_posix_lock ( struct flock *lock, mca_io_ompio_file_t *fh, int op,
             */
             return 0;
         }
-        if ( OMPIO_LOCK_ENTIRE_REGION ) {
+        if ( flags == OMPIO_LOCK_ENTIRE_REGION ) {
             lock->l_start = (off_t) offset;
             lock->l_len   = len;            
         }
@@ -79,13 +82,13 @@ int mca_fbtl_posix_lock ( struct flock *lock, mca_io_ompio_file_t *fh, int op,
                the two into a single lock.
             */
             bmod = offset % fh->f_fs_block_size; 
-            if ( !bmod  ) {
+            if ( bmod  ) {
                 lock->l_start = (off_t) offset;
-                lock->l_len   = fh->f_fs_block_size - bmod;
+                lock->l_len   = bmod;
             }
-            lmod = (offset+len-1)%fh->f_fs_block_size;
-            if ( !lmod ) {
-                if ( bmod ) {
+            lmod = (offset+len)%fh->f_fs_block_size;
+            if ( lmod ) {
+                if ( !bmod ) {
                     lock->l_start = (offset+len-lmod );
                     lock->l_len   = lmod;
                 }
@@ -100,15 +103,28 @@ int mca_fbtl_posix_lock ( struct flock *lock, mca_io_ompio_file_t *fh, int op,
         }
     }
 
+
+#ifdef OMPIO_DEBUG
+    printf("%d: acquiring lock for offset %ld length %ld requested offset %ld request len %ld \n", 
+           fh->f_rank, lock->l_start, lock->l_len, offset, len);
+#endif
     return (fcntl ( fh->fd, F_SETLKW, lock));     
 }
 
 int mca_fbtl_posix_unlock ( struct flock *lock, mca_io_ompio_file_t *fh )
 {
+    int ret;
     if ( -1 == lock->l_start && -1 == lock->l_len ) {
         return 0;
     }
     
     lock->l_type = F_UNLCK;
-    return (fcntl ( fh->fd, F_SETLK, lock));     
+#ifdef OMPIO_DEBUG
+    printf("%d: releasing lock for offset %ld length %ld\n", fh->f_rank, lock->l_start, lock->l_len);
+#endif
+    ret = fcntl ( fh->fd, F_SETLK, lock);     
+    lock->l_start = -1;
+    lock->l_len   = -1;
+
+    return ret;
 }
diff --git a/ompi/mca/fbtl/posix/fbtl_posix_preadv.c b/ompi/mca/fbtl/posix/fbtl_posix_preadv.c
index b6360b3d97..3ebc69cfa3 100644
--- a/ompi/mca/fbtl/posix/fbtl_posix_preadv.c
+++ b/ompi/mca/fbtl/posix/fbtl_posix_preadv.c
@@ -37,7 +37,7 @@ ssize_t mca_fbtl_posix_preadv (mca_io_ompio_file_t *fh )
     OMPI_MPI_OFFSET_TYPE iov_offset = 0;
     ssize_t bytes_read=0, ret_code=0;
     struct flock lock;
-    off_t total_length;
+    off_t total_length, end_offset=0;
 
     if (NULL == fh->f_io_array) {
         return OMPI_ERROR;
@@ -55,6 +55,7 @@ ssize_t mca_fbtl_posix_preadv (mca_io_ompio_file_t *fh )
 	    iov[iov_count].iov_base = fh->f_io_array[i].memory_address;
 	    iov[iov_count].iov_len = fh->f_io_array[i].length;
 	    iov_offset = (OMPI_MPI_OFFSET_TYPE)(intptr_t)fh->f_io_array[i].offset;
+            end_offset = (off_t)fh->f_io_array[i].offset + (off_t)fh->f_io_array[i].length;
 	    iov_count ++;
 	}
 
@@ -77,12 +78,13 @@ ssize_t mca_fbtl_posix_preadv (mca_io_ompio_file_t *fh )
                     iov[iov_count].iov_base =
                         fh->f_io_array[i+1].memory_address;
                     iov[iov_count].iov_len = fh->f_io_array[i+1].length;
+                    end_offset = (off_t)fh->f_io_array[i].offset + (off_t)fh->f_io_array[i].length;
                     iov_count ++;
                     continue;
 	    }
 	}
 
-        total_length = ((off_t)iov[iov_count-1].iov_base + iov[iov_count-1].iov_len - (off_t)iov_offset );
+        total_length = (end_offset - (off_t)iov_offset );
         mca_fbtl_posix_lock ( &lock, fh, F_RDLCK, iov_offset, total_length, OMPIO_LOCK_SELECTIVE ); 
 #if defined(HAVE_PREADV)
 	ret_code = preadv (fh->fd, iov, iov_count, iov_offset);
diff --git a/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c b/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c
index 61d8008355..1c09827bde 100644
--- a/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c
+++ b/ompi/mca/fbtl/posix/fbtl_posix_pwritev.c
@@ -39,7 +39,7 @@ ssize_t  mca_fbtl_posix_pwritev(mca_io_ompio_file_t *fh )
     OMPI_MPI_OFFSET_TYPE iov_offset = 0;
     ssize_t ret_code=0, bytes_written=0;
     struct flock lock;
-    off_t total_length;
+    off_t total_length, end_offset=0;
 
     if (NULL == fh->f_io_array) {
         return OMPI_ERROR;
@@ -57,6 +57,7 @@ ssize_t  mca_fbtl_posix_pwritev(mca_io_ompio_file_t *fh )
 	    iov[iov_count].iov_base = fh->f_io_array[i].memory_address;
 	    iov[iov_count].iov_len = fh->f_io_array[i].length;
 	    iov_offset = (OMPI_MPI_OFFSET_TYPE)(intptr_t)fh->f_io_array[i].offset;
+            end_offset = (off_t)fh->f_io_array[i].offset + (off_t)fh->f_io_array[i].length;
 	    iov_count ++;
 	}
 
@@ -78,6 +79,7 @@ ssize_t  mca_fbtl_posix_pwritev(mca_io_ompio_file_t *fh )
 		 (iov_count < IOV_MAX )) {
 		iov[iov_count].iov_base = fh->f_io_array[i+1].memory_address;
 		iov[iov_count].iov_len  = fh->f_io_array[i+1].length;
+                end_offset = (off_t)fh->f_io_array[i].offset + (off_t)fh->f_io_array[i].length;
                 iov_count ++;
 		continue;
 	    }
@@ -95,7 +97,7 @@ ssize_t  mca_fbtl_posix_pwritev(mca_io_ompio_file_t *fh )
 
 	*/
 
-        total_length = ((off_t)iov[iov_count-1].iov_base + iov[iov_count-1].iov_len - (off_t)iov_offset);
+        total_length = (end_offset - (off_t)iov_offset);
         mca_fbtl_posix_lock ( &lock, fh, F_WRLCK, iov_offset, total_length, OMPIO_LOCK_SELECTIVE ); 
 #if defined (HAVE_PWRITEV) 
 	ret_code = pwritev (fh->fd, iov, iov_count, iov_offset);
diff --git a/ompi/mca/fs/ufs/fs_ufs_file_open.c b/ompi/mca/fs/ufs/fs_ufs_file_open.c
index 8f0ea650c9..b579720d6a 100644
--- a/ompi/mca/fs/ufs/fs_ufs_file_open.c
+++ b/ompi/mca/fs/ufs/fs_ufs_file_open.c
@@ -96,6 +96,10 @@ mca_fs_ufs_file_open (struct ompi_communicator_t *comm,
 
     fh->f_stripe_size=0;
     fh->f_stripe_count=1;
+    /* Need to find a way to determine the file system block size at run time.
+       4096 is the most common value, but it might not always be accurate.
+    */
+    fh->f_fs_block_size = 4096;
 
     return OMPI_SUCCESS;
 }