Brings file locking changes from develop

19 files changed, 590 insertions, 163 deletions

diff --git a/src/H5F.c b/src/H5F.c
index 31e5def..2b3dba1 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -60,9 +60,6 @@
 /* Package Variables */
 /*********************/
 
-/* Package initialization variable */
-hbool_t H5_PKG_INIT_VAR = FALSE;
-
 
 /*****************************/
 /* Library Private Variables */
@@ -74,86 +71,6 @@ hbool_t H5_PKG_INIT_VAR = FALSE;
 /*******************/
 
 
-/* File ID class */
-static const H5I_class_t H5I_FILE_CLS[1] = {{
-    H5I_FILE,                   /* ID class value */
-    0,                          /* Class flags */
-    0,                          /* # of reserved IDs for class */
-    (H5I_free_t)H5F__close_cb   /* Callback routine for closing objects of this class */
-}};
-
-
-/*--------------------------------------------------------------------------
-NAME
-   H5F__init_package -- Initialize interface-specific information
-USAGE
-    herr_t H5F__init_package()
-RETURNS
-    Non-negative on success/Negative on failure
-DESCRIPTION
-    Initializes any interface-specific data or routines.
-
---------------------------------------------------------------------------*/
-herr_t
-H5F__init_package(void)
-{
-    herr_t ret_value = SUCCEED;   /* Return value */
-
-    FUNC_ENTER_PACKAGE
-
-    /*
-     * Initialize the atom group for the file IDs.
-     */
-    if(H5I_register_type(H5I_FILE_CLS) < 0)
-        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "unable to initialize interface")
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* H5F__init_package() */
-
-
-/*-------------------------------------------------------------------------
- * Function:    H5F_term_package
- *
- * Purpose:     Terminate this interface: free all memory and reset global
- *              variables to their initial values.  Release all ID groups
- *              associated with this interface.
- *
- * Return:      Success:    Positive if anything was done that might
- *                          have affected other interfaces;
- *                          zero otherwise.
- *
- *              Failure:    Never fails
- *-------------------------------------------------------------------------
- */
-int
-H5F_term_package(void)
-{
-    int    n = 0;
-
-    FUNC_ENTER_NOAPI_NOINIT_NOERR
-
-    if(H5_PKG_INIT_VAR) {
-        if(H5I_nmembers(H5I_FILE) > 0) {
-            (void)H5I_clear_type(H5I_FILE, FALSE, FALSE);
-            n++; /*H5I*/
-        } /* end if */
-        else {
-            /* Make certain we've cleaned up all the shared file objects */
-            H5F_sfile_assert_num(0);
-
-            /* Destroy the file object id group */
-            n += (H5I_dec_type_ref(H5I_FILE) > 0);
-
-            /* Mark closed */
-            if(0 == n)
-                H5_PKG_INIT_VAR = FALSE;
-        } /* end else */
-    } /* end if */
-
-    FUNC_LEAVE_NOAPI(n)
-} /* end H5F_term_package() */
-
 
 /*-------------------------------------------------------------------------
  * Function:    H5Fget_create_plist
diff --git a/src/H5FD.c b/src/H5FD.c
index 2e80c7f..991b7b7 100644
--- a/src/H5FD.c
+++ b/src/H5FD.c
@@ -1436,7 +1436,7 @@ done:
  *              constant H5P_DEFAULT). The bytes to be written come from the
  *              buffer BUF.
  *
- * Return:      SNon-negative on success/Negative on failure
+ * Return:      Non-negative on success/Negative on failure
  *
  *-------------------------------------------------------------------------
  */
@@ -1642,7 +1642,7 @@ H5FDlock(H5FD_t *file, hbool_t rw)
 
     /* Call private function */
     if(H5FD_lock(file, rw) < 0)
-        HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "file lock request failed")
+        HGOTO_ERROR(H5E_VFL, H5E_CANTLOCKFILE, FAIL, "file lock request failed")
 
 done:
     FUNC_LEAVE_API(ret_value)
@@ -1672,7 +1672,7 @@ H5FD_lock(H5FD_t *file, hbool_t rw)
 
     /* Dispatch to driver */
     if(file->cls->lock && (file->cls->lock)(file, rw) < 0)
-        HGOTO_ERROR(H5E_VFL, H5E_CANTUPDATE, FAIL, "driver lock request failed")
+        HGOTO_ERROR(H5E_VFL, H5E_CANTLOCKFILE, FAIL, "driver lock request failed")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1704,7 +1704,7 @@ H5FDunlock(H5FD_t *file)
 
     /* Call private function */
     if(H5FD_unlock(file) < 0)
-        HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "file unlock request failed")
+        HGOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "file unlock request failed")
 
 done:
     FUNC_LEAVE_API(ret_value)
@@ -1733,7 +1733,7 @@ H5FD_unlock(H5FD_t *file)
 
     /* Dispatch to driver */
     if(file->cls->unlock && (file->cls->unlock)(file) < 0)
-        HGOTO_ERROR(H5E_VFL, H5E_CANTUPDATE, FAIL, "driver unlock request failed")
+        HGOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "driver unlock request failed")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5FDcore.c b/src/H5FDcore.c
index e4a3207..40d838c 100644
--- a/src/H5FDcore.c
+++ b/src/H5FDcore.c
@@ -36,6 +36,9 @@
 /* The driver identification number, initialized at runtime */
 static hid_t H5FD_CORE_g = 0;
 
+/* Whether to ignore file locks when disabled (env var value) */
+static htri_t ignore_disabled_file_locks_s = FAIL;
+
 /* The skip list node type.  Represents a region in the file. */
 typedef struct H5FD_core_region_t {
     haddr_t start;              /* Start address of the region          */
@@ -55,6 +58,7 @@ typedef struct H5FD_core_t {
     size_t  increment;          /* multiples for mem allocation         */
     hbool_t backing_store;      /* write to file name on flush          */
     size_t  bstore_page_size;   /* backing store page size              */
+    hbool_t ignore_disabled_file_locks;
     int     fd;                 /* backing store file descriptor        */
     /* Information for determining uniqueness of a file with a backing store */
 #ifndef H5_HAVE_WIN32_API
@@ -407,9 +411,19 @@ done:
 static herr_t
 H5FD__init_package(void)
 {
+    char    *lock_env_var   = NULL;     /* Environment variable pointer */
     herr_t ret_value = SUCCEED;
 
-    FUNC_ENTER_NOAPI_NOINIT
+    FUNC_ENTER_STATIC
+
+    /* Check the use disabled file locks environment variable */
+    lock_env_var = HDgetenv("HDF5_USE_FILE_LOCKING");
+    if(lock_env_var && !HDstrcmp(lock_env_var, "BEST_EFFORT"))
+        ignore_disabled_file_locks_s = TRUE;    /* Override: Ignore disabled locks */
+    else if(lock_env_var && (!HDstrcmp(lock_env_var, "TRUE") || !HDstrcmp(lock_env_var, "1")))
+        ignore_disabled_file_locks_s = FALSE;   /* Override: Don't ignore disabled locks */
+    else
+        ignore_disabled_file_locks_s = FAIL;    /* Environment variable not set, or not set correctly */
 
     if(H5FD_core_init() < 0)
         HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "unable to initialize core VFD")
@@ -691,6 +705,16 @@ H5FD__core_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxaddr
     /* Save file image callbacks */
     file->fi_callbacks = file_image_info.callbacks;
 
+    /* Check the file locking flags in the fapl */
+    if(ignore_disabled_file_locks_s != FAIL)
+        /* The environment variable was set, so use that preferentially */
+        file->ignore_disabled_file_locks = ignore_disabled_file_locks_s;
+    else {
+        /* Use the value in the property list */
+        if(H5P_get(plist, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, &file->ignore_disabled_file_locks) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTGET, NULL, "can't get ignore disabled file locks property")
+    }
+
     if(fd >= 0) {
         /* Retrieve information for determining uniqueness of file */
 #ifdef H5_HAVE_WIN32_API
@@ -1509,18 +1533,20 @@ H5FD_core_lock(H5FD_t *_file, hbool_t rw)
      * descriptor, this is a no-op.
      */
     if(file->fd >= 0) {
-
         /* Set exclusive or shared lock based on rw status */
         lock_flags = rw ? LOCK_EX : LOCK_SH;
 
         /* Place a non-blocking lock on the file */
         if(HDflock(file->fd, lock_flags | LOCK_NB) < 0) {
-            if(ENOSYS == errno)
-                HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)")
+            if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+                /* When errno is set to ENOSYS, the file system does not support
+                 * locking, so ignore it.
+                 */
+                errno = 0;
+            }
             else
                 HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to lock file")
         } /* end if */
-
     } /* end if */
 
 done:
@@ -1549,16 +1575,17 @@ H5FD_core_unlock(H5FD_t *_file)
 
     HDassert(file);
 
-    if(file->fd >= 0) {
-
+    if(file->fd >= 0)
         if(HDflock(file->fd, LOCK_UN) < 0) {
-            if(ENOSYS == errno)
-                HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)")
+            if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+                /* When errno is set to ENOSYS, the file system does not support
+                 * locking, so ignore it.
+                 */
+                errno = 0;
+            }
             else
                 HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to unlock file")
-        } /* end if */
-
-    } /* end if */
+        }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5FDdirect.c b/src/H5FDdirect.c
index 34c4346..4046050 100644
--- a/src/H5FDdirect.c
+++ b/src/H5FDdirect.c
@@ -38,6 +38,9 @@
 /* The driver identification number, initialized at runtime */
 static hid_t H5FD_DIRECT_g = 0;
 
+/* Whether to ignore file locks when disabled (env var value) */
+static htri_t ignore_disabled_file_locks_s = FAIL;
+
 /* File operations */
 #define OP_UNKNOWN  0
 #define OP_READ    1
@@ -71,6 +74,7 @@ typedef struct H5FD_direct_t {
     haddr_t  pos;      /*current file I/O position  */
     int    op;      /*last operation    */
     H5FD_direct_fapl_t  fa;    /*file access properties  */
+    hbool_t         ignore_disabled_file_locks;
 #ifndef H5_HAVE_WIN32_API
     /*
      * On most systems the combination of device and i-node number uniquely
@@ -193,10 +197,20 @@ DESCRIPTION
 static herr_t
 H5FD__init_package(void)
 {
+    char    *lock_env_var   = NULL;     /* Environment variable pointer */
     herr_t ret_value = SUCCEED;
 
     FUNC_ENTER_STATIC
 
+    /* Check the use disabled file locks environment variable */
+    lock_env_var = HDgetenv("HDF5_USE_FILE_LOCKING");
+    if(lock_env_var && !HDstrcmp(lock_env_var, "BEST_EFFORT"))
+        ignore_disabled_file_locks_s = TRUE;    /* Override: Ignore disabled locks */
+    else if(lock_env_var && (!HDstrcmp(lock_env_var, "TRUE") || !HDstrcmp(lock_env_var, "1")))
+        ignore_disabled_file_locks_s = FALSE;   /* Override: Don't ignore disabled locks */
+    else
+        ignore_disabled_file_locks_s = FAIL;    /* Environment variable not set, or not set correctly */
+
     if(H5FD_direct_init() < 0)
         HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "unable to initialize direct VFD")
 
@@ -518,6 +532,16 @@ H5FD_direct_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxadd
     file->fa.fbsize = fa->fbsize;
     file->fa.cbsize = fa->cbsize;
 
+    /* Check the file locking flags in the fapl */
+    if(ignore_disabled_file_locks_s != FAIL)
+        /* The environment variable was set, so use that preferentially */
+        file->ignore_disabled_file_locks = ignore_disabled_file_locks_s;
+    else {
+        /* Use the value in the property list */
+        if(H5P_get(plist, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, &file->ignore_disabled_file_locks) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTGET, NULL, "can't get ignore disabled file locks property")
+    }
+
     /* Try to decide if data alignment is required.  The reason to check it here
      * is to handle correctly the case that the file is in a different file system
      * than the one where the program is running.
@@ -1335,16 +1359,27 @@ static herr_t
 H5FD_direct_lock(H5FD_t *_file, hbool_t rw)
 {
     H5FD_direct_t  *file = (H5FD_direct_t*)_file;	/* VFD file struct */
-    const int lock = rw ? LOCK_EX : LOCK_SH;
+    int lock_flags;                                 /* file locking flags   */
     herr_t ret_value = SUCCEED;                 	/* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT
 
     HDassert(file);
 
-    /* Place the lock with non-blocking */
-    if(HDflock(file->fd, lock | LOCK_NB) < 0)
-        HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to flock file")
+    /* Set exclusive or shared lock based on rw status */
+    lock_flags = rw ? LOCK_EX : LOCK_SH;
+
+    /* Place a non-blocking lock on the file */
+    if(HDflock(file->fd, lock_flags | LOCK_NB) < 0) {
+        if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
+        }
+        else
+            HSYS_GOTO_ERROR(H5E_VFL, H5E_CANTLOCKFILE, FAIL, "unable to lock file")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1372,8 +1407,16 @@ H5FD_direct_unlock(H5FD_t *_file)
 
     HDassert(file);
 
-    if(HDflock(file->fd, LOCK_UN) < 0)
-        HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to flock (unlock) file")
+    if(HDflock(file->fd, LOCK_UN) < 0) {
+        if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
+        }
+        else
+            HSYS_GOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock file")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5FDfamily.c b/src/H5FDfamily.c
index d110ef7..154878e 100644
--- a/src/H5FDfamily.c
+++ b/src/H5FDfamily.c
@@ -1372,9 +1372,9 @@ H5FD_family_lock(H5FD_t *_file, hbool_t rw)
         for(v = 0; v < u; v++) {
             if(H5FD_unlock(file->memb[v]) < 0)
                 /* Push error, but keep going */
-                HDONE_ERROR(H5E_IO, H5E_CANTUNLOCK, FAIL, "unable to unlock member files")
+                HDONE_ERROR(H5E_IO, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock member files")
         } /* end for */
-        HGOTO_ERROR(H5E_IO, H5E_CANTLOCK, FAIL, "unable to lock member files")
+        HGOTO_ERROR(H5E_IO, H5E_CANTLOCKFILE, FAIL, "unable to lock member files")
     } /* end if */
 
 done:
@@ -1406,7 +1406,7 @@ H5FD_family_unlock(H5FD_t *_file)
     for(u = 0; u < file->nmembs; u++)
         if(file->memb[u])
             if(H5FD_unlock(file->memb[u]) < 0)
-                HGOTO_ERROR(H5E_IO, H5E_CANTUNLOCK, FAIL, "unable to unlock member files")
+                HGOTO_ERROR(H5E_IO, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock member files")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5FDlog.c b/src/H5FDlog.c
index f649bc4..d34a273 100644
--- a/src/H5FDlog.c
+++ b/src/H5FDlog.c
@@ -40,6 +40,9 @@
 /* The driver identification number, initialized at runtime */
 static hid_t H5FD_LOG_g = 0;
 
+/* Whether to ignore file locks when disabled (env var value) */
+static htri_t ignore_disabled_file_locks_s = FAIL;
+
 /* Driver-specific file access properties */
 typedef struct H5FD_log_fapl_t {
     char *logfile;              /* Allocated log file name */
@@ -80,6 +83,7 @@ typedef struct H5FD_log_t {
     haddr_t         eof;    /* end of file; current file size   */
     haddr_t         pos;    /* current file I/O position        */
     H5FD_file_op_t  op;     /* last operation                   */
+    hbool_t         ignore_disabled_file_locks;
     char            filename[H5FD_MAX_FILENAME_LEN];    /* Copy of file name from open operation */
 #ifndef H5_HAVE_WIN32_API
     /* On most systems the combination of device and i-node number uniquely
@@ -234,10 +238,20 @@ H5FL_DEFINE_STATIC(H5FD_log_t);
 static herr_t
 H5FD__init_package(void)
 {
+    char    *lock_env_var   = NULL;     /* Environment variable pointer */
     herr_t ret_value = SUCCEED;
 
     FUNC_ENTER_STATIC
 
+    /* Check the use disabled file locks environment variable */
+    lock_env_var = HDgetenv("HDF5_USE_FILE_LOCKING");
+    if(lock_env_var && !HDstrcmp(lock_env_var, "BEST_EFFORT"))
+        ignore_disabled_file_locks_s = TRUE;    /* Override: Ignore disabled locks */
+    else if(lock_env_var && (!HDstrcmp(lock_env_var, "TRUE") || !HDstrcmp(lock_env_var, "1")))
+        ignore_disabled_file_locks_s = FALSE;   /* Override: Don't ignore disabled locks */
+    else
+        ignore_disabled_file_locks_s = FAIL;    /* Environment variable not set, or not set correctly */
+
     if(H5FD_log_init() < 0)
         HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "unable to initialize log VFD")
 
@@ -640,6 +654,16 @@ H5FD_log_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxaddr)
 
     } /* end if */
 
+    /* Check the file locking flags in the fapl */
+    if(ignore_disabled_file_locks_s != FAIL)
+        /* The environment variable was set, so use that preferentially */
+        file->ignore_disabled_file_locks = ignore_disabled_file_locks_s;
+    else {
+        /* Use the value in the property list */
+        if(H5P_get(plist, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, &file->ignore_disabled_file_locks) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTGET, NULL, "can't get ignore disabled file locks property")
+    }
+
     /* Check for non-default FAPL */
     if(H5P_FILE_ACCESS_DEFAULT != fapl_id) {
         /* This step is for h5repart tool only. If user wants to change file driver from
@@ -1713,11 +1737,15 @@ H5FD_log_lock(H5FD_t *_file, hbool_t rw)
 
     /* Place a non-blocking lock on the file */
     if(HDflock(file->fd, lock_flags | LOCK_NB) < 0) {
-        if(ENOSYS == errno)
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)")
+        if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
+        }
         else
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to lock file")
-    } /* end if */
+            HSYS_GOTO_ERROR(H5E_VFL, H5E_CANTLOCKFILE, FAIL, "unable to lock file")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -1746,11 +1774,15 @@ H5FD_log_unlock(H5FD_t *_file)
     HDassert(file);
 
     if(HDflock(file->fd, LOCK_UN) < 0) {
-        if(ENOSYS == errno)
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)")
+        if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
+        }
         else
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to unlock file")
-    } /* end if */
+            HSYS_GOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock file")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5FDmulti.c b/src/H5FDmulti.c
index 72f4da5..f80cac5 100644
--- a/src/H5FDmulti.c
+++ b/src/H5FDmulti.c
@@ -1856,7 +1856,7 @@ H5FD_multi_lock(H5FD_t *_file, hbool_t rw)
     } /* end if */
 
     if(nerrors)
-        H5Epush_ret(func, H5E_ERR_CLS, H5E_INTERNAL, H5E_BADVALUE, "error locking member files", -1)
+        H5Epush_ret(func, H5E_ERR_CLS, H5E_VFL, H5E_CANTLOCKFILE, "error locking member files", -1)
     return 0;
 
 } /* H5FD_multi_lock() */
@@ -1893,7 +1893,7 @@ H5FD_multi_unlock(H5FD_t *_file)
     } END_MEMBERS;
 
     if(nerrors)
-        H5Epush_ret(func, H5E_ERR_CLS, H5E_INTERNAL, H5E_BADVALUE, "error unlocking member files", -1)
+        H5Epush_ret(func, H5E_ERR_CLS, H5E_VFL, H5E_CANTUNLOCKFILE, "error unlocking member files", -1)
 
     return 0;
 } /* H5FD_multi_unlock() */
diff --git a/src/H5FDsec2.c b/src/H5FDsec2.c
index ba4750e..cbb707a 100644
--- a/src/H5FDsec2.c
+++ b/src/H5FDsec2.c
@@ -39,6 +39,9 @@
 /* The driver identification number, initialized at runtime */
 static hid_t H5FD_SEC2_g = 0;
 
+/* Whether to ignore file locks when disabled (env var value) */
+static htri_t ignore_disabled_file_locks_s = FAIL;
+
 /* The description of a file belonging to this driver. The 'eoa' and 'eof'
  * determine the amount of hdf5 address space in use and the high-water mark
  * of the file (the current size of the underlying filesystem file). The
@@ -57,6 +60,7 @@ typedef struct H5FD_sec2_t {
     haddr_t         eof;    /* end of file; current file size   */
     haddr_t         pos;    /* current file I/O position        */
     H5FD_file_op_t  op;     /* last operation                   */
+    hbool_t         ignore_disabled_file_locks;
     char            filename[H5FD_MAX_FILENAME_LEN];    /* Copy of file name from open operation */
 #ifndef H5_HAVE_WIN32_API
     /* On most systems the combination of device and i-node number uniquely
@@ -190,10 +194,20 @@ H5FL_DEFINE_STATIC(H5FD_sec2_t);
 static herr_t
 H5FD__init_package(void)
 {
+    char    *lock_env_var   = NULL;     /* Environment variable pointer */
     herr_t ret_value = SUCCEED;
 
     FUNC_ENTER_STATIC
 
+    /* Check the use disabled file locks environment variable */
+    lock_env_var = HDgetenv("HDF5_USE_FILE_LOCKING");
+    if(lock_env_var && !HDstrcmp(lock_env_var, "BEST_EFFORT"))
+        ignore_disabled_file_locks_s = TRUE;    /* Override: Ignore disabled locks */
+    else if(lock_env_var && (!HDstrcmp(lock_env_var, "TRUE") || !HDstrcmp(lock_env_var, "1")))
+        ignore_disabled_file_locks_s = FALSE;   /* Override: Don't ignore disabled locks */
+    else
+        ignore_disabled_file_locks_s = FAIL;    /* Environment variable not set, or not set correctly */
+
     if(H5FD_sec2_init() < 0)
         HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "unable to initialize sec2 VFD")
 
@@ -316,6 +330,7 @@ H5FD_sec2_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxaddr)
     struct _BY_HANDLE_FILE_INFORMATION fileinfo;
 #endif
     h5_stat_t       sb;
+    H5P_genplist_t  *plist;                 /* Property list pointer */
     H5FD_t          *ret_value = NULL;          /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT
@@ -373,17 +388,26 @@ H5FD_sec2_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxaddr)
     file->inode = sb.st_ino;
 #endif /* H5_HAVE_WIN32_API */
 
+    /* Get the FAPL */
+    if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl_id)))
+        HGOTO_ERROR(H5E_VFL, H5E_BADTYPE, NULL, "not a file access property list")
+
+    /* Check the file locking flags in the fapl */
+    if(ignore_disabled_file_locks_s != FAIL)
+        /* The environment variable was set, so use that preferentially */
+        file->ignore_disabled_file_locks = ignore_disabled_file_locks_s;
+    else {
+        /* Use the value in the property list */
+        if(H5P_get(plist, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, &file->ignore_disabled_file_locks) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTGET, NULL, "can't get ignore disabled file locks property")
+    }
+
     /* Retain a copy of the name used to open the file, for possible error reporting */
     HDstrncpy(file->filename, name, sizeof(file->filename));
     file->filename[sizeof(file->filename) - 1] = '\0';
 
     /* Check for non-default FAPL */
     if(H5P_FILE_ACCESS_DEFAULT != fapl_id) {
-        H5P_genplist_t      *plist;      /* Property list pointer */
-
-        /* Get the FAPL */
-        if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl_id)))
-            HGOTO_ERROR(H5E_VFL, H5E_BADTYPE, NULL, "not a file access property list")
 
         /* This step is for h5repart tool only. If user wants to change file driver from
          * family to one that uses single files (sec2, etc.) while using h5repart, this
@@ -955,11 +979,15 @@ H5FD_sec2_lock(H5FD_t *_file, hbool_t rw)
 
     /* Place a non-blocking lock on the file */
     if(HDflock(file->fd, lock_flags | LOCK_NB) < 0) {
-        if(ENOSYS == errno)
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)")
+        if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
+        }
         else
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to lock file")
-    } /* end if */
+            HSYS_GOTO_ERROR(H5E_VFL, H5E_CANTLOCKFILE, FAIL, "unable to lock file")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -988,11 +1016,15 @@ H5FD_sec2_unlock(H5FD_t *_file)
     HDassert(file);
 
     if(HDflock(file->fd, LOCK_UN) < 0) {
-        if(ENOSYS == errno)
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)")
+        if(file->ignore_disabled_file_locks && ENOSYS == errno) {
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
+        }
         else
-            HSYS_GOTO_ERROR(H5E_FILE, H5E_BADFILE, FAIL, "unable to unlock file")
-    } /* end if */
+            HSYS_GOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock file")
+    }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
diff --git a/src/H5FDstdio.c b/src/H5FDstdio.c
index d29a1b4..a769e86 100644
--- a/src/H5FDstdio.c
+++ b/src/H5FDstdio.c
@@ -52,6 +52,9 @@
 /* The driver identification number, initialized at runtime */
 static hid_t H5FD_STDIO_g = 0;
 
+/* Whether to ignore file locks when disabled (env var value) */
+static htri_t ignore_disabled_file_locks_s = -1;
+
 /* The maximum number of bytes which can be written in a single I/O operation */
 static size_t H5_STDIO_MAX_IO_BYTES_g = (size_t)-1;
 
@@ -82,6 +85,7 @@ typedef struct H5FD_stdio_t {
     haddr_t     eof;            /* end of file; current file size   */
     haddr_t     pos;            /* current file I/O position        */
     unsigned    write_access;   /* Flag to indicate the file was opened with write access */
+    hbool_t     ignore_disabled_file_locks;
     H5FD_stdio_file_op op;  /* last operation */
 #ifndef H5_HAVE_WIN32_API
     /* On most systems the combination of device and i-node number uniquely
@@ -231,11 +235,23 @@ static const H5FD_class_t H5FD_stdio_g = {
 hid_t
 H5FD_stdio_init(void)
 {
+    char    *lock_env_var   = NULL;     /* Environment variable pointer */
+
     /* Clear the error stack */
     H5Eclear2(H5E_DEFAULT);
 
-    if (H5I_VFL!=H5Iget_type(H5FD_STDIO_g))
+    /* Check the use disabled file locks environment variable */
+    lock_env_var = getenv("HDF5_USE_FILE_LOCKING");
+    if(lock_env_var && !strcmp(lock_env_var, "BEST_EFFORT"))
+        ignore_disabled_file_locks_s = 1;       /* Override: Ignore disabled locks */
+    else if(lock_env_var && (!strcmp(lock_env_var, "TRUE") || !strcmp(lock_env_var, "1")))
+        ignore_disabled_file_locks_s = 0;       /* Override: Don't ignore disabled locks */
+    else
+        ignore_disabled_file_locks_s = -1;      /* Environment variable not set, or not set correctly */
+
+    if (H5I_VFL != H5Iget_type(H5FD_STDIO_g))
         H5FD_STDIO_g = H5FDregister(&H5FD_stdio_g);
+
     return H5FD_STDIO_g;
 } /* end H5FD_stdio_init() */
 
@@ -318,7 +334,7 @@ H5Pset_fapl_stdio(hid_t fapl_id)
  *-------------------------------------------------------------------------
  */
 static H5FD_t *
-H5FD_stdio_open( const char *name, unsigned flags, hid_t /*UNUSED*/ fapl_id,
+H5FD_stdio_open( const char *name, unsigned flags, hid_t fapl_id,
     haddr_t maxaddr)
 {
     FILE                *f = NULL;
@@ -396,6 +412,21 @@ H5FD_stdio_open( const char *name, unsigned flags, hid_t /*UNUSED*/ fapl_id,
         file->eof = (haddr_t)x;
     }
 
+    /* Check the file locking flags in the fapl */
+    if(ignore_disabled_file_locks_s != -1)
+        /* The environment variable was set, so use that preferentially */
+        file->ignore_disabled_file_locks = ignore_disabled_file_locks_s;
+    else {
+        hbool_t unused;
+
+        /* Use the value in the property list */
+        if(H5Pget_file_locking(fapl_id, &unused, &file->ignore_disabled_file_locks) < 0) {
+            free(file);
+            fclose(f);
+            H5Epush_ret(func, H5E_ERR_CLS, H5E_FILE, H5E_CANTGET, "unable to get use disabled file locks property", NULL);
+        }
+    }
+
     /* Get the file descriptor (needed for truncate and some Windows information) */
 #ifdef H5_HAVE_WIN32_API
     file->fd = _fileno(file->fp);
@@ -1104,10 +1135,13 @@ H5FD_stdio_lock(H5FD_t *_file, hbool_t rw)
 
     /* Place a non-blocking lock on the file */
     if(flock(file->fd, lock_flags | LOCK_NB) < 0) {
-        if(ENOSYS == errno)
-            H5Epush_ret(func, H5E_ERR_CLS, H5E_IO, H5E_FCNTL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)", -1)
+        if(file->ignore_disabled_file_locks && ENOSYS == errno)
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
         else
-            H5Epush_ret(func, H5E_ERR_CLS, H5E_IO, H5E_FCNTL, "file lock failed", -1)
+            H5Epush_ret(func, H5E_ERR_CLS, H5E_VFL, H5E_CANTLOCKFILE, "file lock failed", -1)
     } /* end if */
 
     /* Flush the stream */
@@ -1152,10 +1186,13 @@ H5FD_stdio_unlock(H5FD_t *_file)
 
     /* Place a non-blocking lock on the file */
     if(flock(file->fd, LOCK_UN) < 0) {
-        if(ENOSYS == errno)
-            H5Epush_ret(func, H5E_ERR_CLS, H5E_IO, H5E_FCNTL, "file locking disabled on this file system (use HDF5_USE_FILE_LOCKING environment variable to override)", -1)
+        if(file->ignore_disabled_file_locks && ENOSYS == errno)
+            /* When errno is set to ENOSYS, the file system does not support
+             * locking, so ignore it.
+             */
+            errno = 0;
         else
-            H5Epush_ret(func, H5E_ERR_CLS, H5E_IO, H5E_FCNTL, "file unlock failed", -1)
+            H5Epush_ret(func, H5E_ERR_CLS, H5E_VFL, H5E_CANTUNLOCKFILE, "file unlock failed", -1)
     } /* end if */
 
 #endif /* H5_HAVE_FLOCK */
diff --git a/src/H5Fint.c b/src/H5Fint.c
index eb023d6..29bbd45 100644
--- a/src/H5Fint.c
+++ b/src/H5Fint.c
@@ -77,6 +77,7 @@ static herr_t H5F__get_objects(const H5F_t *f, unsigned types, size_t max_index,
 static int H5F__get_objects_cb(void *obj_ptr, hid_t obj_id, void *key);
 static herr_t H5F__build_name(const char *prefix, const char *file_name, char **full_name/*out*/);
 static char *H5F__getenv_prefix_name(char **env_prefix/*in,out*/);
+static herr_t H5F__check_if_using_file_locks(H5P_genplist_t *fapl, hbool_t *use_file_locking);
 static herr_t H5F__build_actual_name(const H5F_t *f, const H5P_genplist_t *fapl, const char *name, char ** /*out*/ actual_name);
 static herr_t H5F__flush_phase1(H5F_t *f);
 static herr_t H5F__flush_phase2(H5F_t *f, hbool_t closing);
@@ -86,6 +87,15 @@ static herr_t H5F__flush_phase2(H5F_t *f, hbool_t closing);
 /* Package Variables */
 /*********************/
 
+/* Package initialization variable */
+hbool_t H5_PKG_INIT_VAR = FALSE;
+
+/* Based on the value of the HDF5_USE_FILE_LOCKING environment variable.
+ * TRUE/FALSE have obvious meanings. FAIL means the environment variable was
+ * not set, so the code should ignore it and use the fapl value instead.
+ */
+htri_t use_locks_env_g = FAIL;
+
 
 /*****************************/
 /* Library Private Variables */
@@ -102,6 +112,123 @@ H5FL_DEFINE(H5F_t);
 /* Declare a free list to manage the H5F_shared_t struct */
 H5FL_DEFINE(H5F_shared_t);
 
+/* File ID class */
+static const H5I_class_t H5I_FILE_CLS[1] = {{
+    H5I_FILE,                   /* ID class value */
+    0,                          /* Class flags */
+    0,                          /* # of reserved IDs for class */
+    (H5I_free_t)H5F__close_cb   /* Callback routine for closing objects of this class */
+}};
+
+
+
+/*--------------------------------------------------------------------------
+NAME
+   H5F__init_package -- Initialize interface-specific information
+USAGE
+    herr_t H5F__init_package()
+RETURNS
+    Non-negative on success/Negative on failure
+DESCRIPTION
+    Initializes any interface-specific data or routines.
+
+--------------------------------------------------------------------------*/
+herr_t
+H5F__init_package(void)
+{
+    herr_t  ret_value       = SUCCEED;  /* Return value */
+
+    FUNC_ENTER_PACKAGE
+
+    /*
+     * Initialize the atom group for the file IDs.
+     */
+    if(H5I_register_type(H5I_FILE_CLS) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTINIT, FAIL, "unable to initialize interface")
+
+    /* Check the file locking environment variable */
+    if(H5F__parse_file_lock_env_var(&use_locks_env_g) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, "unable to parse file locking environment variable")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5F__init_package() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5F_term_package
+ *
+ * Purpose:     Terminate this interface: free all memory and reset global
+ *              variables to their initial values.  Release all ID groups
+ *              associated with this interface.
+ *
+ * Return:      Success:    Positive if anything was done that might
+ *                          have affected other interfaces;
+ *                          zero otherwise.
+ *
+ *              Failure:    Never fails
+ *
+ *-------------------------------------------------------------------------
+ */
+int
+H5F_term_package(void)
+{
+    int    n = 0;
+
+    FUNC_ENTER_NOAPI_NOINIT_NOERR
+
+    if(H5_PKG_INIT_VAR) {
+        if(H5I_nmembers(H5I_FILE) > 0) {
+            (void)H5I_clear_type(H5I_FILE, FALSE, FALSE);
+            n++; /*H5I*/
+        } /* end if */
+        else {
+            /* Make certain we've cleaned up all the shared file objects */
+            H5F_sfile_assert_num(0);
+
+            /* Destroy the file object id group */
+            n += (H5I_dec_type_ref(H5I_FILE) > 0);
+
+            /* Mark closed */
+            if(0 == n)
+                H5_PKG_INIT_VAR = FALSE;
+        } /* end else */
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI(n)
+} /* end H5F_term_package() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5F__parse_file_lock_env_var
+ *
+ * Purpose:     Parses the HDF5_USE_FILE_LOCKING environment variable.
+ *
+ * NOTE:        This is done in a separate function so we can call it from
+ *              the test code.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5F__parse_file_lock_env_var(htri_t *use_locks)
+{
+    char    *lock_env_var   = NULL;     /* Environment variable pointer */
+
+    FUNC_ENTER_PACKAGE_NOERR
+
+    /* Check the file locking environment variable */
+    lock_env_var = HDgetenv("HDF5_USE_FILE_LOCKING");
+    if(lock_env_var && (!HDstrcmp(lock_env_var, "FALSE") || !HDstrcmp(lock_env_var, "0")))
+        *use_locks = FALSE;    /* Override: Never use locks */
+    else if(lock_env_var && (!HDstrcmp(lock_env_var, "TRUE") || !HDstrcmp(lock_env_var, "BEST_EFFORT") || !HDstrcmp(lock_env_var, "1")))
+        *use_locks = TRUE;     /* Override: Always use locks */
+    else
+        *use_locks = FAIL;      /* Environment variable not set, or not set correctly */
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5F__parse_file_lock_env_var() */
 
 
 /*-------------------------------------------------------------------------
@@ -1334,6 +1461,52 @@ H5F__dest(H5F_t *f, hbool_t flush)
 
 
 /*-------------------------------------------------------------------------
+ * Function:    H5F__check_if_using_file_locks
+ *
+ * Purpose:     Determines if this file will use file locks.
+ *
+ * There are three ways that file locking can be controlled:
+ *
+ * 1) The configure/cmake option that sets the H5_USE_FILE_LOCKING
+ *    symbol (which is used as the default fapl value).
+ *
+ * 2) The H5Pset_file_locking() API call, which will override
+ *    the configuration default.
+ *
+ * 3) The HDF5_USE_FILE_LOCKING environment variable, which overrides
+ *    everything above.
+ *
+ * The main reason to disable file locking is to prevent errors on file
+ * systems where locking is not supported or has been disabled (as is
+ * often the case in parallel file systems).
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5F__check_if_using_file_locks(H5P_genplist_t *fapl, hbool_t *use_file_locking)
+{
+    herr_t  ret_value       = SUCCEED;      /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    /* Make sure the out parameter has a value */
+    *use_file_locking = TRUE;
+
+    /* Check the fapl property */
+    if(H5P_get(fapl, H5F_ACS_USE_FILE_LOCKING_NAME, use_file_locking) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, "can't get use file locking flag")
+
+    /* Check the environment variable */
+    if(use_locks_env_g != FAIL)
+        *use_file_locking = (use_locks_env_g == TRUE) ? TRUE : FALSE;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5F__check_if_using_file_locks() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5F_open
  *
  * Purpose:    Opens (or creates) a file.  This function understands the
@@ -1422,8 +1595,7 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id)
     hbool_t             set_flag = FALSE;   /*set the status_flags in the superblock */
     hbool_t             clear = FALSE;      /*clear the status_flags         */
     hbool_t             evict_on_close;     /* evict on close value from plist  */
-    char               *lock_env_var = NULL;/*env var pointer               */
-    hbool_t             use_file_locking;   /*read from env var             */
+    hbool_t             use_file_locking = TRUE;    /* Using file locks? */
     hbool_t             ci_load = FALSE;    /* whether MDC ci load requested */
     hbool_t             ci_write = FALSE;   /* whether MDC CI write requested */
     H5F_t              *ret_value = NULL;   /*actual return value           */
@@ -1441,15 +1613,13 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id)
     if(NULL == (drvr = H5FD_get_class(fapl_id)))
         HGOTO_ERROR(H5E_FILE, H5E_CANTGET, NULL, "unable to retrieve VFL class")
 
-    /* Check the environment variable that determines if we care
-     * about file locking. File locking should be used unless explicitly
-     * disabled.
-     */
-    lock_env_var = HDgetenv("HDF5_USE_FILE_LOCKING");
-    if(lock_env_var && !HDstrcmp(lock_env_var, "FALSE"))
-        use_file_locking = FALSE;
-    else
-        use_file_locking = TRUE;
+    /* Get the file access property list, for future queries */
+    if(NULL == (a_plist = (H5P_genplist_t *)H5I_object(fapl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not file access property list")
+
+    /* Check if we are using file locking */
+    if (H5F__check_if_using_file_locks(a_plist, &use_file_locking) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, NULL, "unable to get file locking flag")
 
     /*
      * Opening a file is a two step process. First we try to open the
@@ -1540,8 +1710,8 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id)
             if(H5FD_lock(lf, (hbool_t)((flags & H5F_ACC_RDWR) ? TRUE : FALSE)) < 0) {
                 /* Locking failed - Closing will remove the lock */
                 if(H5FD_close(lf) < 0)
-                    HDONE_ERROR(H5E_FILE, H5E_CANTOPENFILE, NULL, "unable to close low-level file info")
-                HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, NULL, "unable to lock the file")
+                    HDONE_ERROR(H5E_FILE, H5E_CANTCLOSEFILE, NULL, "unable to close low-level file info")
+                HGOTO_ERROR(H5E_FILE, H5E_CANTLOCKFILE, NULL, "unable to lock the file")
             } /* end if */
 
         /* Create the 'top' file structure */
@@ -1573,10 +1743,6 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id)
     shared = file->shared;
     lf = shared->lf;
 
-    /* Get the file access property list, for future queries */
-    if(NULL == (a_plist = (H5P_genplist_t *)H5I_object(fapl_id)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not file access property list")
-
     /* Check if page buffering is enabled */
     if(H5P_get(a_plist, H5F_ACS_PAGE_BUFFER_SIZE_NAME, &page_buf_size) < 0)
         HGOTO_ERROR(H5E_FILE, H5E_CANTGET, NULL, "can't get page buffer size")
@@ -1715,7 +1881,7 @@ H5F_open(const char *name, unsigned flags, hid_t fcpl_id, hid_t fapl_id)
             /* Remove the file lock for SWMR_WRITE */
             if(use_file_locking && (H5F_INTENT(file) & H5F_ACC_SWMR_WRITE)) {
                 if(H5FD_unlock(file->shared->lf) < 0)
-                    HGOTO_ERROR(H5E_FILE, H5E_CANTOPENFILE, NULL, "unable to unlock the file")
+                    HGOTO_ERROR(H5E_FILE, H5E_CANTUNLOCKFILE, NULL, "unable to unlock the file")
             } /* end if */
         } /* end if */
         else { /* H5F_ACC_RDONLY: check consistency of status_flags */
diff --git a/src/H5Fpkg.h b/src/H5Fpkg.h
index e4892ed..6e3f3d4 100644
--- a/src/H5Fpkg.h
+++ b/src/H5Fpkg.h
@@ -389,6 +389,10 @@ H5FL_EXTERN(H5F_t);
 /* Declare a free list to manage the H5F_shared_t struct */
 H5FL_EXTERN(H5F_shared_t);
 
+/* Whether or not to use file locking (based on the environment variable)
+ * FAIL means ignore the environment variable.
+ */
+H5_DLLVAR htri_t use_locks_env_g;
 
 /******************************/
 /* Package Private Prototypes */
@@ -407,6 +411,7 @@ H5_DLL herr_t H5F__start_swmr_write(H5F_t *f);
 H5_DLL herr_t H5F__close(hid_t file_id);
 H5_DLL herr_t H5F__close_cb(H5F_t *f);
 H5_DLL herr_t H5F__set_libver_bounds(H5F_t *f, H5F_libver_t low, H5F_libver_t high);
+H5_DLL herr_t H5F__parse_file_lock_env_var(htri_t *use_locks);
 
 /* File mount related routines */
 H5_DLL herr_t H5F__mount(H5G_loc_t *loc, const char *name, H5F_t *child, hid_t plist_id);
@@ -466,6 +471,7 @@ H5_DLL herr_t H5F__get_sohm_mesg_count_test(hid_t fid, unsigned type_id, size_t
 H5_DLL herr_t H5F__check_cached_stab_test(hid_t file_id);
 H5_DLL herr_t H5F__get_maxaddr_test(hid_t file_id, haddr_t *maxaddr);
 H5_DLL herr_t H5F__get_sbe_addr_test(hid_t file_id, haddr_t *sbe_addr);
+H5_DLL herr_t H5F__reparse_file_lock_variable_test(void);
 #endif /* H5F_TESTING */
 
 #endif /* _H5Fpkg_H */
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index 57318a7..fd161e2 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -516,6 +516,8 @@ typedef struct H5F_t H5F_t;
 #define H5F_ACS_PAGE_BUFFER_SIZE_NAME           "page_buffer_size" /* the maximum size for the page buffer cache */
 #define H5F_ACS_PAGE_BUFFER_MIN_META_PERC_NAME  "page_buffer_min_meta_perc" /* the min metadata percentage for the page buffer cache */
 #define H5F_ACS_PAGE_BUFFER_MIN_RAW_PERC_NAME   "page_buffer_min_raw_perc" /* the min raw data percentage for the page buffer cache */
+#define H5F_ACS_USE_FILE_LOCKING_NAME           "use_file_locking" /* whether or not we use file locks for SWMR control and to prevent multiple writers */
+#define H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME "ignore_disabled_file_locks" /* whether or not we ignore "locks disabled" errors */
 
 /* ======================== File Mount properties ====================*/
 #define H5F_MNT_SYM_LOCAL_NAME         "local"                 /* Whether absolute symlinks local to file. */
diff --git a/src/H5Ftest.c b/src/H5Ftest.c
index df9c933..e9d697a 100644
--- a/src/H5Ftest.c
+++ b/src/H5Ftest.c
@@ -232,3 +232,36 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5F__get_sbe_addr_test() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5F__reparse_file_lock_variable_test
+ *
+ * Purpose:     Re-parse the file locking environment variable.
+ *
+ *              Since getenv(3) is fairly expensive, we only parse it once,
+ *              when the library opens. This test function is used to
+ *              re-parse the environment variable after we've changed it
+ *              with setnev(3).
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ * Programmer:	Dana Robinson
+ *              Summer 2020
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5F__reparse_file_lock_variable_test(void)
+{
+    herr_t ret_value = SUCCEED;
+
+    FUNC_ENTER_PACKAGE
+
+    /* Check the file locking environment variable */
+    if(H5F__parse_file_lock_env_var(&use_locks_env_g) < 0)
+        HGOTO_ERROR(H5E_FILE, H5E_CANTGET, FAIL, "unable to parse file locking environment variable")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5F__reparse_file_lock_variable_test() */
+
diff --git a/src/H5Pfapl.c b/src/H5Pfapl.c
index b2a1a30..208c8dd 100644
--- a/src/H5Pfapl.c
+++ b/src/H5Pfapl.c
@@ -259,6 +259,29 @@
 #define H5F_ACS_PAGE_BUFFER_MIN_RAW_PERC_DEF            0
 #define H5F_ACS_PAGE_BUFFER_MIN_RAW_PERC_ENC            H5P__encode_unsigned
 #define H5F_ACS_PAGE_BUFFER_MIN_RAW_PERC_DEC            H5P__decode_unsigned
+/* Definition for using file locking or not. The default is set
+ * via the configure step.
+ */
+#define H5F_ACS_USE_FILE_LOCKING_SIZE                   sizeof(hbool_t)
+#if defined H5_USE_FILE_LOCKING && H5_USE_FILE_LOCKING
+#define H5F_ACS_USE_FILE_LOCKING_DEF                    TRUE
+#else
+#define H5F_ACS_USE_FILE_LOCKING_DEF                    FALSE
+#endif
+#define H5F_ACS_USE_FILE_LOCKING_ENC                    H5P__encode_hbool_t
+#define H5F_ACS_USE_FILE_LOCKING_DEC                    H5P__decode_hbool_t
+/* Definition for whether we ignore file locking errors when we can
+ * tell that file locking has been disabled on the file system.
+ * The default is set via the configure step.
+ */
+#define H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_SIZE         sizeof(hbool_t)
+#if defined H5_IGNORE_DISABLED_FILE_LOCKS && H5_IGNORE_DISABLED_FILE_LOCKS
+#define H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_DEF          TRUE
+#else
+#define H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_DEF          FALSE
+#endif
+#define H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_ENC          H5P__encode_hbool_t
+#define H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_DEC          H5P__decode_hbool_t
 
 
 /******************/
@@ -398,6 +421,8 @@ static const H5AC_cache_image_config_t H5F_def_mdc_initCacheImageCfg_g = H5F_ACS
 static const size_t H5F_def_page_buf_size_g = H5F_ACS_PAGE_BUFFER_SIZE_DEF;      /* Default page buffer size */
 static const unsigned H5F_def_page_buf_min_meta_perc_g = H5F_ACS_PAGE_BUFFER_MIN_META_PERC_DEF;      /* Default page buffer minimum metadata size */
 static const unsigned H5F_def_page_buf_min_raw_perc_g = H5F_ACS_PAGE_BUFFER_MIN_RAW_PERC_DEF;      /* Default page buffer mininum raw data size */
+static const hbool_t H5F_def_use_file_locking_g = H5F_ACS_USE_FILE_LOCKING_DEF;                 /* Default use file locking flag */
+static const hbool_t H5F_def_ignore_disabled_file_locks_g = H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_DEF;     /* Default ignore disabled file locks flag */
 
 
 /*-------------------------------------------------------------------------
@@ -647,6 +672,16 @@ H5P__facc_reg_prop(H5P_genclass_t *pclass)
             NULL, NULL, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
+    /* Register the use file locking flag */
+    if(H5P__register_real(pclass, H5F_ACS_USE_FILE_LOCKING_NAME, H5F_ACS_USE_FILE_LOCKING_SIZE, &H5F_def_use_file_locking_g,
+            NULL, NULL, NULL, H5F_ACS_USE_FILE_LOCKING_ENC, H5F_ACS_USE_FILE_LOCKING_DEC, NULL, NULL, NULL, NULL) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
+    /* Register the ignore disabled file locks flag */
+    if(H5P__register_real(pclass, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_SIZE, &H5F_def_ignore_disabled_file_locks_g,
+            NULL, NULL, NULL, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_ENC, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_DEC, NULL, NULL, NULL, NULL) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5P__facc_reg_prop() */
@@ -4586,6 +4621,98 @@ done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Pget_evict_on_close() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pset_file_locking
+ *
+ * Purpose:     Sets the file locking property values.
+ *
+ *              Overrides the default file locking flag setting that was
+ *              set when the library was configured.
+ *
+ *              Can be overridden by the HDF5_USE_FILE_LOCKING environment
+ *              variable.
+ *
+ *              File locking is used when creating/opening a file to prevent
+ *              problematic file accesses.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ * Programmer:  Dana Robinson
+ *              Spring 2020
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pset_file_locking(hid_t fapl_id, hbool_t use_file_locking, hbool_t ignore_when_disabled)
+{
+    H5P_genplist_t *plist;          /* property list pointer */
+    herr_t ret_value = SUCCEED;     /* return value */
+
+    FUNC_ENTER_API(FAIL)
+    H5TRACE3("e", "ibb", fapl_id, use_file_locking, ignore_when_disabled);
+
+    /* Make sure this is a fapl */
+    if(TRUE != H5P_isa_class(fapl_id, H5P_FILE_ACCESS))
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTREGISTER, FAIL, "property list is not a file access plist")
+
+    /* Get the plist structure */
+    if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl_id)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Set values */
+    if(H5P_set(plist, H5F_ACS_USE_FILE_LOCKING_NAME, &use_file_locking) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set use file locking property")
+    if(H5P_set(plist, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, &ignore_when_disabled) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "can't set ignore disabled file locks property")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pset_file_locking() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pget_file_locking
+ *
+ * Purpose:     Gets the file locking property values.
+ *
+ *              File locking is used when creating/opening a file to prevent
+ *              problematic file accesses.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ * Programmer:  Dana Robinson
+ *              Spring 2020
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_file_locking(hid_t fapl_id, hbool_t *use_file_locking, hbool_t *ignore_when_disabled)
+{
+    H5P_genplist_t *plist;          /* property list pointer */
+    herr_t ret_value = SUCCEED;     /* return value */
+
+    FUNC_ENTER_API(FAIL)
+    H5TRACE3("e", "i*b*b", fapl_id, use_file_locking, ignore_when_disabled);
+
+    /* Make sure this is a fapl */
+    if(TRUE != H5P_isa_class(fapl_id, H5P_FILE_ACCESS))
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTREGISTER, FAIL, "property list is not an access plist")
+
+    /* Get the plist structure */
+    if(NULL == (plist = (H5P_genplist_t *)H5I_object(fapl_id)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Get values */
+    if(H5P_get(plist, H5F_ACS_USE_FILE_LOCKING_NAME, use_file_locking) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get use file locking property")
+    if(H5P_get(plist, H5F_ACS_IGNORE_DISABLED_FILE_LOCKS_NAME, ignore_when_disabled) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get ignore disabled file locks property")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_file_locking() */
+
 #ifdef H5_HAVE_PARALLEL
 
 /*-------------------------------------------------------------------------
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index 5d6dea8..dbd0724 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -359,6 +359,8 @@ H5_DLL herr_t H5Pset_mdc_log_options(hid_t plist_id, hbool_t is_enabled, const c
 H5_DLL herr_t H5Pget_mdc_log_options(hid_t plist_id, hbool_t *is_enabled, char *location, size_t *location_size, hbool_t *start_on_access);
 H5_DLL herr_t H5Pset_evict_on_close(hid_t fapl_id, hbool_t evict_on_close);
 H5_DLL herr_t H5Pget_evict_on_close(hid_t fapl_id, hbool_t *evict_on_close);
+H5_DLL herr_t H5Pset_file_locking(hid_t fapl_id, hbool_t use_file_locking, hbool_t ignore_when_disabled);
+H5_DLL herr_t H5Pget_file_locking(hid_t fapl_id, hbool_t *use_file_locking, hbool_t *ignore_when_disabled);
 #ifdef H5_HAVE_PARALLEL
 H5_DLL herr_t H5Pset_all_coll_metadata_ops(hid_t plist_id, hbool_t is_collective);
 H5_DLL herr_t H5Pget_all_coll_metadata_ops(hid_t plist_id, hbool_t *is_collective);
diff --git a/src/H5err.txt b/src/H5err.txt
index 30c646f..f3cca72 100644
--- a/src/H5err.txt
+++ b/src/H5err.txt
@@ -133,6 +133,8 @@ MINOR, FILEACC, H5E_NOTHDF5, Not an HDF5 file
 MINOR, FILEACC, H5E_BADFILE, Bad file ID accessed
 MINOR, FILEACC, H5E_TRUNCATED, File has been truncated
 MINOR, FILEACC, H5E_MOUNT, File mount error
+MINOR, FILEACC, H5E_CANTLOCKFILE, Unable to lock file
+MINOR, FILEACC, H5E_CANTUNLOCKFILE, Unable to unlock file
 
 # Generic low-level file I/O errors
 MINOR, FILE, H5E_SEEKERROR, Seek failed
diff --git a/src/H5private.h b/src/H5private.h
index c0d39fc..78746c3 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -863,8 +863,8 @@ H5_DLL H5_ATTR_CONST int Nflock(int fd, int operation);
 #ifndef HDflock
     /* NOTE: flock(2) is not present on all POSIX systems.
      * If it is not present, we try a flock() equivalent based on
-     * fcntl(2), then fall back to a function that always fails if
-     * it is not present at all (Windows uses a separate Wflock()
+     * fcntl(2), then fall back to a function that always succeeds
+     * if it is not present at all (Windows uses a separate Wflock()
      * function).
      */
     #if defined(H5_HAVE_FLOCK)
diff --git a/src/H5system.c b/src/H5system.c
index a7ca3f8..dfb8d21 100644
--- a/src/H5system.c
+++ b/src/H5system.c
@@ -647,14 +647,14 @@ Pflock(int fd, int operation) {
  * Purpose:     Wrapper function for systems where no file locking is
  *              available.
  *
- * Return:      Failure:    -1 (always fails)
+ * Return:      0 (success)
  *
  *-------------------------------------------------------------------------
  */
 int H5_ATTR_CONST
 Nflock(int H5_ATTR_UNUSED fd, int H5_ATTR_UNUSED operation) {
-    /* just fail */
-    return -1;
+    /* just succeed */
+    return 0;
 } /* end Nflock() */
 
 
diff --git a/src/libhdf5.settings.in b/src/libhdf5.settings.in
index 422ca0b..b1c1b2b 100644
--- a/src/libhdf5.settings.in
+++ b/src/libhdf5.settings.in
@@ -87,5 +87,6 @@ Parallel Filtered Dataset Writes: @PARALLEL_FILTERED_WRITES@
             Using memory checker: @USINGMEMCHECKER@
  Memory allocation sanity checks: @MEMORYALLOCSANITYCHECK@
           Function stack tracing: @CODESTACK@
+                Use file locking: @DESIRED_FILE_LOCKING@
        Strict file format checks: @STRICT_FORMAT_CHECKS@
     Optimization instrumentation: @INSTRUMENT_LIBRARY@