Brings splitter VFD from develop

6 files changed, 1453 insertions, 2 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 9ff16c9..34afd42 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -230,6 +230,7 @@ set (H5FD_SOURCES
     ${HDF5_SRC_DIR}/H5FDs3comms.c
     ${HDF5_SRC_DIR}/H5FDsec2.c
     ${HDF5_SRC_DIR}/H5FDspace.c
+    ${HDF5_SRC_DIR}/H5FDsplitter.c
     ${HDF5_SRC_DIR}/H5FDstdio.c
     ${HDF5_SRC_DIR}/H5FDtest.c
     ${HDF5_SRC_DIR}/H5FDwindows.c
@@ -248,6 +249,7 @@ set (H5FD_HDRS
     ${HDF5_SRC_DIR}/H5FDros3.h
     ${HDF5_SRC_DIR}/H5FDs3comms.h
     ${HDF5_SRC_DIR}/H5FDsec2.h
+    ${HDF5_SRC_DIR}/H5FDsplitter.h
     ${HDF5_SRC_DIR}/H5FDstdio.h
     ${HDF5_SRC_DIR}/H5FDwindows.h
 )
diff --git a/src/H5FDpublic.h b/src/H5FDpublic.h
index 54ca8f7..61bf212 100644
--- a/src/H5FDpublic.h
+++ b/src/H5FDpublic.h
@@ -255,6 +255,8 @@ typedef enum H5F_mem_t	H5FD_mem_t;
      * that creates a file which is compatible with the default VFD.
      * Generally, this means that the VFD creates a single file that follows
      * the canonical HDF5 file format.
+     * Regarding the Splitter VFD specifically, only drivers with this flag
+     * enabled may be used as the Write-Only (W/O) channel driver.
      */
 #define H5FD_FEAT_DEFAULT_VFD_COMPATIBLE        0x00008000
 
diff --git a/src/H5FDsplitter.c b/src/H5FDsplitter.c
new file mode 100644
index 0000000..d0ed250d
--- /dev/null
+++ b/src/H5FDsplitter.c
@@ -0,0 +1,1346 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*
+ * Purpose:     The Splitter VFD implements a file driver which relays all the
+ *              VFD calls to an underlying VFD, and send all the write calls to
+ *              another underlying VFD. Maintains two files simultaneously.
+ */
+
+/* This source code file is part of the H5FD driver module */
+#include "H5FDdrvr_module.h"
+
+#include "H5private.h"      /* Generic Functions        */
+#include "H5Eprivate.h"     /* Error handling           */
+#include "H5Fprivate.h"     /* File access              */
+#include "H5FDprivate.h"    /* File drivers             */
+#include "H5FDsplitter.h"   /* Splitter file driver     */
+#include "H5FLprivate.h"    /* Free Lists               */
+#include "H5Iprivate.h"     /* IDs                      */
+#include "H5MMprivate.h"    /* Memory management        */
+#include "H5Pprivate.h"     /* Property lists           */
+
+/* The driver identification number, initialized at runtime */
+static hid_t H5FD_SPLITTER_g = 0;
+
+/* Driver-specific file access properties */
+typedef struct H5FD_splitter_fapl_t {
+    hid_t rw_fapl_id;   /* fapl for the R/W channel       */
+    hid_t wo_fapl_id;   /* fapl for the W/O channel       */
+    char wo_path[H5FD_SPLITTER_PATH_MAX + 1]; /* file name for the W/O channel */
+    char log_file_path[H5FD_SPLITTER_PATH_MAX + 1]; /* file to record errors reported by the W/O channel */
+    hbool_t ignore_wo_errs; /* TRUE to ignore errors on the W/O channel */
+} H5FD_splitter_fapl_t;
+
+/* The information of this splitter */
+typedef struct H5FD_splitter_t {
+    H5FD_t pub;         /* public stuff, must be first    */
+    unsigned version;   /* version of the H5FD_splitter_vfd_config_t structure used */
+    H5FD_splitter_fapl_t fa; /* driver-specific file access properties */
+    H5FD_t  *rw_file;   /* pointer of R/W channel */
+    H5FD_t  *wo_file;   /* pointer of W/O channel */
+    FILE    *logfp;     /* Log file pointer */
+} H5FD_splitter_t;
+
+/*
+ * These macros check for overflow of various quantities.  These macros
+ * assume that HDoff_t is signed and haddr_t and size_t are unsigned.
+ *
+ * ADDR_OVERFLOW:   Checks whether a file address of type `haddr_t'
+ *                  is too large to be represented by the second argument
+ *                  of the file seek function.
+ *
+ * SIZE_OVERFLOW:   Checks whether a buffer size of type `hsize_t' is too
+ *                  large to be represented by the `size_t' type.
+ *
+ * REGION_OVERFLOW: Checks whether an address and size pair describe data
+ *                  which can be addressed entirely by the second
+ *                  argument of the file seek function.
+ */
+#define MAXADDR (((haddr_t)1<<(8*sizeof(HDoff_t)-1))-1)
+#define ADDR_OVERFLOW(A)    (HADDR_UNDEF==(A) || ((A) & ~(haddr_t)MAXADDR))
+#define SIZE_OVERFLOW(Z)    ((Z) & ~(hsize_t)MAXADDR)
+#define REGION_OVERFLOW(A,Z)    (ADDR_OVERFLOW(A) || SIZE_OVERFLOW(Z) ||    \
+                                 HADDR_UNDEF==(A)+(Z) ||                    \
+                                (HDoff_t)((A)+(Z))<(HDoff_t)(A))
+
+/* This macro provides a wrapper for shared fail-log-ignore behavior
+ * for errors arising in the splitter's W/O channel.
+ * Logs an error entry in a log file, if the file exists.
+ * If not set to ignore errors, registers an error with the library.
+ */
+#define H5FD_SPLITTER_WO_ERROR(file, funcname, errmajor, errminor, ret, mesg) \
+{                                                                             \
+    H5FD__splitter_log_error((file), (funcname), (mesg));                     \
+    if(FALSE == (file)->fa.ignore_wo_errs)                                    \
+        HGOTO_ERROR((errmajor), (errminor), (ret), (mesg))                    \
+}
+
+#define H5FD_SPLITTER_DEBUG_OP_CALLS 0 /* debugging print toggle; 0 disables */
+
+#if H5FD_SPLITTER_DEBUG_OP_CALLS
+#define H5FD_SPLITTER_LOG_CALL(name) do { \
+    HDprintf("called %s()\n", (name));    \
+    HDfflush(stdout);                     \
+} while (0)
+#else
+#define H5FD_SPLITTER_LOG_CALL(name) /* no-op */
+#endif /* H5FD_SPLITTER_DEBUG_OP_CALLS */
+
+/* Private functions */
+
+/* Print error messages from W/O channel to log file */
+static herr_t H5FD__splitter_log_error(const H5FD_splitter_t *file, const char *atfunc, const char *msg);
+static int H5FD__copy_plist(hid_t fapl_id, hid_t *id_out_ptr);
+
+/* Prototypes */
+static herr_t H5FD__splitter_term(void);
+static hsize_t H5FD__splitter_sb_size(H5FD_t *_file);
+static herr_t H5FD__splitter_sb_encode(H5FD_t *_file, char *name/*out*/, unsigned char *buf/*out*/);
+static herr_t H5FD__splitter_sb_decode(H5FD_t *_file, const char *name, const unsigned char *buf);
+static void *H5FD__splitter_fapl_get(H5FD_t *_file);
+static void *H5FD__splitter_fapl_copy(const void *_old_fa);
+static herr_t H5FD__splitter_fapl_free(void *_fapl);
+static H5FD_t *H5FD__splitter_open(const char *name, unsigned flags, hid_t fapl_id, haddr_t maxaddr);
+static herr_t H5FD__splitter_close(H5FD_t *_file);
+static int H5FD__splitter_cmp(const H5FD_t *_f1, const H5FD_t *_f2);
+static herr_t H5FD__splitter_query(const H5FD_t *_file, unsigned long *flags /* out */);
+static herr_t H5FD__splitter_get_type_map(const H5FD_t *_file, H5FD_mem_t *type_map);
+static haddr_t H5FD__splitter_alloc(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, hsize_t size);
+static herr_t H5FD__splitter_free(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, hsize_t size);
+static haddr_t H5FD__splitter_get_eoa(const H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type);
+static herr_t H5FD__splitter_set_eoa(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type, haddr_t addr);
+static haddr_t H5FD__splitter_get_eof(const H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type);
+static herr_t H5FD__splitter_get_handle(H5FD_t *_file, hid_t H5_ATTR_UNUSED fapl, void** file_handle);
+static herr_t H5FD__splitter_read(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t size, void *buf);
+static herr_t H5FD__splitter_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t size, const void *buf);
+static herr_t H5FD__splitter_flush(H5FD_t *_file, hid_t dxpl_id, hbool_t closing);
+static herr_t H5FD__splitter_truncate(H5FD_t *_file, hid_t dxpl_id, hbool_t closing);
+static herr_t H5FD__splitter_lock(H5FD_t *_file, hbool_t rw);
+static herr_t H5FD__splitter_unlock(H5FD_t *_file);
+
+static const H5FD_class_t H5FD_splitter_g = {
+    "splitter",                 /* name                 */
+    MAXADDR,                    /* maxaddr              */
+    H5F_CLOSE_WEAK,             /* fc_degree            */
+    H5FD__splitter_term,        /* terminate            */
+    H5FD__splitter_sb_size,     /* sb_size              */
+    H5FD__splitter_sb_encode,   /* sb_encode            */
+    H5FD__splitter_sb_decode,   /* sb_decode            */
+    sizeof(H5FD_splitter_fapl_t), /* fapl_size          */
+    H5FD__splitter_fapl_get,    /* fapl_get             */
+    H5FD__splitter_fapl_copy,   /* fapl_copy            */
+    H5FD__splitter_fapl_free,   /* fapl_free            */
+    0,                          /* dxpl_size            */
+    NULL,                       /* dxpl_copy            */
+    NULL,                       /* dxpl_free            */
+    H5FD__splitter_open,        /* open                 */
+    H5FD__splitter_close,       /* close                */
+    H5FD__splitter_cmp,         /* cmp                  */
+    H5FD__splitter_query,       /* query                */
+    H5FD__splitter_get_type_map, /* get_type_map        */
+    H5FD__splitter_alloc,       /* alloc                */
+    H5FD__splitter_free,        /* free                 */
+    H5FD__splitter_get_eoa,     /* get_eoa              */
+    H5FD__splitter_set_eoa,     /* set_eoa              */
+    H5FD__splitter_get_eof,     /* get_eof              */
+    H5FD__splitter_get_handle,  /* get_handle           */
+    H5FD__splitter_read,        /* read                 */
+    H5FD__splitter_write,       /* write                */
+    H5FD__splitter_flush,       /* flush                */
+    H5FD__splitter_truncate,    /* truncate             */
+    H5FD__splitter_lock,        /* lock                 */
+    H5FD__splitter_unlock,      /* unlock               */
+    H5FD_FLMAP_DICHOTOMY        /* fl_map               */
+};
+
+/* Declare a free list to manage the H5FD_splitter_t struct */
+H5FL_DEFINE_STATIC(H5FD_splitter_t);
+
+/* Declare a free list to manage the H5FD_splitter_fapl_t struct */
+H5FL_DEFINE_STATIC(H5FD_splitter_fapl_t);
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__init_package
+ *
+ * Purpose:     Initializes any interface-specific data or routines.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__init_package(void)
+{
+    herr_t ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    if(H5FD_splitter_init() < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "unable to initialize splitter VFD")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5FD__init_package() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD_splitter_init
+ *
+ * Purpose:     Initialize the splitter driver by registering it with the
+ *              library.
+ *
+ * Return:      Success:    The driver ID for the splitter driver.
+ *              Failure:    Negative
+ *-------------------------------------------------------------------------
+ */
+hid_t
+H5FD_splitter_init(void)
+{
+    hid_t ret_value = H5I_INVALID_HID;
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    if(H5I_VFL != H5I_get_type(H5FD_SPLITTER_g))
+        H5FD_SPLITTER_g = H5FDregister(&H5FD_splitter_g);
+
+    ret_value = H5FD_SPLITTER_g;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD_splitter_init() */
+
+
+/*---------------------------------------------------------------------------
+ * Function:    H5FD__splitter_term
+ *
+ * Purpose:     Shut down the splitter VFD.
+ *
+ * Returns:     SUCCEED (Can't fail)
+ *---------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_term(void)
+{
+    FUNC_ENTER_STATIC_NOERR
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Reset VFL ID */
+    H5FD_SPLITTER_g = 0;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5FD__splitter_term() */
+
+
+ /*-------------------------------------------------------------------------
+ * Function:    H5FD__copy_plist
+ *
+ * Purpose:     Sanity-wrapped H5P_copy_plist() for each channel.
+ *              Utility function for operation in multiple locations.
+ *
+ * Return:      0 on success, -1 on error.
+ *-------------------------------------------------------------------------
+ */
+static int
+H5FD__copy_plist(hid_t   fapl_id,
+                 hid_t  *id_out_ptr)
+{
+    int                 ret_value = 0;
+    H5P_genplist_t     *plist_ptr = NULL;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    HDassert(id_out_ptr != NULL);
+
+    if(FALSE == H5P_isa_class(fapl_id, H5P_FILE_ACCESS))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, -1, "not a file access property list");
+
+    plist_ptr = (H5P_genplist_t *)H5I_object(fapl_id);
+    if(NULL == plist_ptr)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, -1, "unable to get property list");
+
+    *id_out_ptr = H5P_copy_plist(plist_ptr, FALSE);
+    if(H5I_INVALID_HID == *id_out_ptr)
+        HGOTO_ERROR(H5E_VFL, H5E_BADTYPE, -1, "unable to copy file access property list");
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value);
+} /* end H5FD__copy_plist() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pset_fapl_splitter
+ *
+ * Purpose:     Sets the file access property list to use the
+ *              splitter driver.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pset_fapl_splitter(hid_t fapl_id, H5FD_splitter_vfd_config_t *vfd_config)
+{
+    H5FD_splitter_fapl_t *info = NULL;
+    H5P_genplist_t       *plist_ptr = NULL;
+    herr_t                ret_value = SUCCEED;
+
+    FUNC_ENTER_API(FAIL)
+    H5TRACE2("e", "i*Dr", fapl_id, vfd_config);
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    if(H5FD_SPLITTER_MAGIC != vfd_config->magic)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid configuration (magic number mismatch)")
+    if(H5FD_CURR_SPLITTER_VFD_CONFIG_VERSION != vfd_config->version)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid config (version number mismatch)")
+    if(NULL == (plist_ptr = (H5P_genplist_t *)H5I_object(fapl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a valid property list")
+
+    /* Make sure that the W/O channel supports write-only capability.
+     * Some drivers (e.g. family or multi) do revision of the superblock
+     * in-memory, causing problems in that channel.
+     * Uses the feature flag H5FD_FEAT_DEFAULT_VFD_COMPATIBLE as the
+     * determining attribute.
+     */
+    if(H5P_DEFAULT != vfd_config->wo_fapl_id) {
+        H5FD_class_t       *wo_driver = NULL;
+        H5FD_driver_prop_t  wo_driver_prop;
+        H5P_genplist_t     *wo_plist_ptr = NULL;
+        unsigned long       wo_driver_flags = 0;
+
+        wo_plist_ptr = (H5P_genplist_t *)H5I_object(vfd_config->wo_fapl_id);
+        if(NULL == wo_plist_ptr)
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
+        if(H5P_peek(wo_plist_ptr, H5F_ACS_FILE_DRV_NAME, &wo_driver_prop) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "can't get driver ID & info")
+        wo_driver = (H5FD_class_t *)H5I_object(wo_driver_prop.driver_id);
+        if(NULL == wo_driver)
+            HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, FAIL, "invalid driver ID in file access property list")
+        if(H5FD_driver_query(wo_driver, &wo_driver_flags) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, FAIL, "can't query VFD flags")
+        if(0 == (H5FD_FEAT_DEFAULT_VFD_COMPATIBLE & wo_driver_flags))
+            HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, FAIL, "unsuitable W/O driver")
+    } /* end if W/O VFD is non-default */
+
+    info = H5FL_CALLOC(H5FD_splitter_fapl_t);
+    if(NULL == info)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTALLOC, FAIL, "unable to allocate file access property list struct")
+
+    info->ignore_wo_errs = vfd_config->ignore_wo_errs;
+    HDstrncpy(info->wo_path, vfd_config->wo_path, H5FD_SPLITTER_PATH_MAX);
+    HDstrncpy(info->log_file_path, vfd_config->log_file_path, H5FD_SPLITTER_PATH_MAX);
+    info->rw_fapl_id = H5P_FILE_ACCESS_DEFAULT; /* pre-set value */
+    info->wo_fapl_id = H5P_FILE_ACCESS_DEFAULT; /* pre-set value */
+
+    /* Set non-default channel FAPL IDs in splitter configuration info */
+    if(H5P_DEFAULT != vfd_config->rw_fapl_id) {
+        if(FALSE == H5P_isa_class(vfd_config->rw_fapl_id, H5P_FILE_ACCESS))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access list")
+        info->rw_fapl_id = vfd_config->rw_fapl_id;
+    }
+    if(H5P_DEFAULT != vfd_config->wo_fapl_id) {
+        if(FALSE == H5P_isa_class(vfd_config->wo_fapl_id, H5P_FILE_ACCESS))
+            HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access list")
+        info->wo_fapl_id = vfd_config->wo_fapl_id;
+    }
+
+    ret_value = H5P_set_driver(plist_ptr, H5FD_SPLITTER, info);
+
+done:
+    if(info)
+        info = H5FL_FREE(H5FD_splitter_fapl_t, info);
+
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pset_fapl_splitter() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5Pget_fapl_splitter
+ *
+ * Purpose:     Returns information about the splitter file access property
+ *              list through the structure config_out.
+ *
+ *              Will fail if config_out is received without pre-set valid
+ *              magic and version information.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_fapl_splitter(hid_t fapl_id, H5FD_splitter_vfd_config_t *config_out)
+{
+    const H5FD_splitter_fapl_t *fapl_ptr  = NULL;
+    H5P_genplist_t             *plist_ptr = NULL;
+    herr_t                      ret_value = SUCCEED;
+
+    FUNC_ENTER_API(FAIL)
+    H5TRACE2("e", "i*Dr", fapl_id, config_out);
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    if(TRUE != H5P_isa_class(fapl_id, H5P_FILE_ACCESS))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
+    if(config_out == NULL)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "config_out pointer is null")
+    if(H5FD_SPLITTER_MAGIC != config_out->magic)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "info-out pointer invalid (magic number mismatch)")
+    if(H5FD_CURR_SPLITTER_VFD_CONFIG_VERSION != config_out->version)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "info-out pointer invalid (version unsafe)")
+
+    /* Pre-set out FAPL IDs with intent to replace these values */
+    config_out->rw_fapl_id = H5I_INVALID_HID;
+    config_out->wo_fapl_id = H5I_INVALID_HID;
+
+    /* Check and get the splitter fapl */
+    if(NULL == (plist_ptr = H5P_object_verify(fapl_id, H5P_FILE_ACCESS)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a file access property list")
+    if(H5FD_SPLITTER != H5P_peek_driver(plist_ptr))
+        HGOTO_ERROR(H5E_PLIST, H5E_BADVALUE, FAIL, "incorrect VFL driver")
+    if(NULL == (fapl_ptr = (const H5FD_splitter_fapl_t *)H5P_peek_driver_info(plist_ptr)))
+        HGOTO_ERROR(H5E_PLIST, H5E_BADVALUE, FAIL, "unable to get specific-driver info")
+
+    HDstrncpy(config_out->wo_path, fapl_ptr->wo_path, H5FD_SPLITTER_PATH_MAX);
+    HDstrncpy(config_out->log_file_path, fapl_ptr->log_file_path, H5FD_SPLITTER_PATH_MAX);
+    config_out->ignore_wo_errs = fapl_ptr->ignore_wo_errs;
+
+    /* Copy R/W and W/O FAPLs */
+    if(H5FD__copy_plist(fapl_ptr->rw_fapl_id, &(config_out->rw_fapl_id)) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, FAIL, "can't copy R/W FAPL");
+    if(H5FD__copy_plist(fapl_ptr->wo_fapl_id, &(config_out->wo_fapl_id)) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, FAIL, "can't copy W/O FAPL");
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_fapl_splitter() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_flush
+ *
+ * Purpose:     Flushes all data to disk for both channels.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_flush(H5FD_t *_file, hid_t H5_ATTR_UNUSED dxpl_id, hbool_t closing)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;
+    herr_t      ret_value = SUCCEED;       /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Public API for dxpl "context" */
+    if(H5FDflush(file->rw_file, dxpl_id, closing) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTFLUSH, FAIL, "unable to flush R/W file")
+    if(H5FDflush(file->wo_file, dxpl_id, closing) < 0)
+       H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTFLUSH, FAIL, "unable to flush W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_flush() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_read
+ *
+ * Purpose:     Reads SIZE bytes of data from the R/W channel, beginning at
+ *              address ADDR into buffer BUF according to data transfer
+ *              properties in DXPL_ID.
+ *
+ * Return:      Success:    SUCCEED
+ *                          The read result is written into the BUF buffer
+ *                          which should be allocated by the caller.
+ *              Failure:    FAIL
+ *                          The contents of BUF are undefined.
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_read(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type,
+    hid_t H5_ATTR_UNUSED dxpl_id, haddr_t addr, size_t size, void *buf)
+{
+    H5FD_splitter_t *file       = (H5FD_splitter_t *)_file;
+    herr_t          ret_value   = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    HDassert(file && file->pub.cls);
+    HDassert(buf);
+
+    /* Check for overflow conditions */
+    if(!H5F_addr_defined(addr))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "addr undefined, addr = %llu", (unsigned long long)addr)
+    if(REGION_OVERFLOW(addr, size))
+        HGOTO_ERROR(H5E_ARGS, H5E_OVERFLOW, FAIL, "addr overflow, addr = %llu", (unsigned long long)addr)
+
+    /* Only read from R/W channel */
+    /* Public API for dxpl "context" */
+    if(H5FDread(file->rw_file, type, dxpl_id, addr, size, buf) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_READERROR, FAIL, "Reading from R/W channel failed")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_read() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_write
+ *
+ * Purpose:     Writes SIZE bytes of data to R/W and W/O channels, beginning
+ *              at address ADDR from buffer BUF according to data transfer
+ *              properties in DXPL_ID.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_write(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id,
+    haddr_t addr, size_t size, const void *buf)
+{
+    H5FD_splitter_t *file      = (H5FD_splitter_t *)_file;
+    H5P_genplist_t  *plist_ptr     = NULL;
+    herr_t           ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    if(NULL == (plist_ptr = (H5P_genplist_t *)H5I_object(dxpl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a property list")
+
+    /* Write to each file */
+    /* Public API for dxpl "context" */
+    if(H5FDwrite(file->rw_file, type, dxpl_id, addr, size, buf) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "R/W file write failed")
+    if(H5FDwrite(file->wo_file, type, dxpl_id, addr, size, buf) < 0)
+       H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_WRITEERROR, FAIL, "unable to write W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_write() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_fapl_get
+ *
+ * Purpose:     Returns a file access property list which indicates how the
+ *              specified file is being accessed. The return list could be
+ *              used to access another file the same way.
+ *
+ * Return:      Success:    Ptr to new file access property list with all
+ *                          members copied from the file struct.
+ *              Failure:    NULL
+ *-------------------------------------------------------------------------
+ */
+static void *
+H5FD__splitter_fapl_get(H5FD_t *_file)
+{
+    H5FD_splitter_t *file      = (H5FD_splitter_t *)_file;
+    void            *ret_value = NULL;
+
+    FUNC_ENTER_STATIC_NOERR
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    ret_value = H5FD__splitter_fapl_copy(&(file->fa));
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_fapl_get() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_fapl_copy
+ *
+ * Purpose:     Copies the file access properties.
+ *
+ * Return:      Success:    Pointer to a new property list info structure.
+ *              Failure:    NULL
+ *-------------------------------------------------------------------------
+ */
+static void *
+H5FD__splitter_fapl_copy(const void *_old_fa)
+{
+    const H5FD_splitter_fapl_t *old_fa_ptr = (const H5FD_splitter_fapl_t *)_old_fa;
+    H5FD_splitter_fapl_t       *new_fa_ptr = NULL;
+    void                       *ret_value  = NULL;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    HDassert(old_fa_ptr);
+
+    new_fa_ptr = H5FL_CALLOC(H5FD_splitter_fapl_t);
+    if(NULL == new_fa_ptr)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTALLOC, NULL, "unable to allocate log file FAPL")
+
+    HDmemcpy(new_fa_ptr, old_fa_ptr, sizeof(H5FD_splitter_fapl_t));
+    HDstrncpy(new_fa_ptr->wo_path, old_fa_ptr->wo_path, H5FD_SPLITTER_PATH_MAX);
+    HDstrncpy(new_fa_ptr->log_file_path, old_fa_ptr->log_file_path, H5FD_SPLITTER_PATH_MAX);
+
+    /* Copy R/W and W/O FAPLs */
+    if(H5FD__copy_plist(old_fa_ptr->rw_fapl_id, &(new_fa_ptr->rw_fapl_id)) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, NULL, "can't copy R/W FAPL");
+    if(H5FD__copy_plist(old_fa_ptr->wo_fapl_id, &(new_fa_ptr->wo_fapl_id)) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, NULL, "can't copy W/O FAPL");
+
+    ret_value = (void *)new_fa_ptr;
+
+done:
+    if(NULL == ret_value)
+        if(new_fa_ptr)
+            new_fa_ptr = H5FL_FREE(H5FD_splitter_fapl_t, new_fa_ptr);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_fapl_copy() */
+
+
+/*--------------------------------------------------------------------------
+ * Function:    H5FD__splitter_fapl_free
+ *
+ * Purpose:     Releases the file access lists
+ *
+ * Return:      SUCCEED/FAIL
+ *--------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_fapl_free(void *_fapl)
+{
+    H5FD_splitter_fapl_t *fapl      = (H5FD_splitter_fapl_t*)_fapl;
+    herr_t                ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(fapl);
+
+    if(H5I_dec_ref(fapl->rw_fapl_id) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTDEC, FAIL, "can't close R/W FAPL ID")
+    if(H5I_dec_ref(fapl->wo_fapl_id) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTDEC, FAIL, "can't close W/O FAPL ID")
+
+    /* Free the property list */
+    fapl = H5FL_FREE(H5FD_splitter_fapl_t, fapl);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_fapl_free() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_open
+ *
+ * Purpose:     Create and/or opens a file as an HDF5 file.
+ *
+ * Return:      Success:    A pointer to a new file data structure. The
+ *                          public fields will be initialized by the
+ *                          caller, which is always H5FD_open().
+ *              Failure:    NULL
+ *-------------------------------------------------------------------------
+ */
+static H5FD_t *
+H5FD__splitter_open(const char *name, unsigned flags, hid_t splitter_fapl_id, haddr_t maxaddr)
+{
+    H5FD_splitter_t            *file_ptr  = NULL; /* Splitter VFD info */
+    const H5FD_splitter_fapl_t *fapl_ptr  = NULL; /* Driver-specific property list */
+    H5P_genplist_t     *plist_ptr = NULL;
+    H5FD_t     *ret_value = NULL;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    if(!name || !*name)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, NULL, "invalid file name")
+    if(0 == maxaddr || HADDR_UNDEF == maxaddr)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADRANGE, NULL, "bogus maxaddr")
+    if(ADDR_OVERFLOW(maxaddr))
+        HGOTO_ERROR(H5E_ARGS, H5E_OVERFLOW, NULL, "bogus maxaddr")
+    if((H5P_FILE_ACCESS_DEFAULT == splitter_fapl_id) ||
+            (H5FD_SPLITTER != H5Pget_driver(splitter_fapl_id)) )
+        /* presupposes that H5P_FILE_ACCESS_DEFAULT is not a splitter */
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, NULL, "driver is not splitter")
+
+    file_ptr = (H5FD_splitter_t *)H5FL_CALLOC(H5FD_splitter_t);
+    if(NULL == file_ptr)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTALLOC, NULL, "unable to allocate file struct")
+    file_ptr->fa.rw_fapl_id = H5I_INVALID_HID;
+    file_ptr->fa.wo_fapl_id = H5I_INVALID_HID;
+
+    /* Get the driver-specific file access properties */
+    plist_ptr = (H5P_genplist_t *)H5I_object(splitter_fapl_id);
+    if(NULL == plist_ptr)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, NULL, "not a file access property list")
+    fapl_ptr = (const H5FD_splitter_fapl_t *)H5P_peek_driver_info(plist_ptr);
+    if(NULL == fapl_ptr)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, NULL, "unable to get VFL driver info")
+
+    /* Copy simpler info */
+    HDstrncpy(file_ptr->fa.wo_path, fapl_ptr->wo_path, H5FD_SPLITTER_PATH_MAX);
+    HDstrncpy(file_ptr->fa.log_file_path, fapl_ptr->log_file_path, H5FD_SPLITTER_PATH_MAX);
+    file_ptr->fa.ignore_wo_errs = fapl_ptr->ignore_wo_errs;
+
+    /* Copy R/W and W/O channel FAPLs. */
+    if(H5FD__copy_plist(fapl_ptr->rw_fapl_id, &(file_ptr->fa.rw_fapl_id)) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, NULL, "can't copy R/W FAPL");
+    if(H5FD__copy_plist(fapl_ptr->wo_fapl_id, &(file_ptr->fa.wo_fapl_id)) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, NULL, "can't copy W/O FAPL");
+
+    /* Prepare log file if necessary.
+     * If application wants to ignore the errors from W/O channel and
+     * provided a name for the log file, then open it
+     */
+    if(!file_ptr->logfp) {
+        if(file_ptr->fa.log_file_path[0] != '\0') {
+            file_ptr->logfp = HDfopen(file_ptr->fa.log_file_path, "w");
+            if(file_ptr->logfp == NULL)
+                HGOTO_ERROR(H5E_VFL, H5E_CANTOPENFILE, NULL, "unable to open log file")
+        } /* end if logfile path given */
+    } /* end if logfile pointer/handle does not exist */
+
+    file_ptr->rw_file = H5FD_open(name, flags, fapl_ptr->rw_fapl_id, HADDR_UNDEF);
+    if(!file_ptr->rw_file)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTOPENFILE, NULL, "unable to open R/W file")
+
+    file_ptr->wo_file = H5FD_open(fapl_ptr->wo_path, flags, fapl_ptr->wo_fapl_id, HADDR_UNDEF);
+    if(!file_ptr->wo_file)
+       H5FD_SPLITTER_WO_ERROR(file_ptr, FUNC, H5E_VFL, H5E_CANTOPENFILE, NULL, "unable to open W/O file")
+
+    ret_value = (H5FD_t*)file_ptr;
+
+done:
+    if(NULL == ret_value) {
+        if(file_ptr) {
+            if(H5I_INVALID_HID != file_ptr->fa.rw_fapl_id)
+                H5I_dec_ref(file_ptr->fa.rw_fapl_id);
+            if(H5I_INVALID_HID != file_ptr->fa.wo_fapl_id)
+                H5I_dec_ref(file_ptr->fa.wo_fapl_id);
+            if(file_ptr->rw_file)
+                H5FD_close(file_ptr->rw_file);
+            if(file_ptr->wo_file)
+                H5FD_close(file_ptr->wo_file);
+            if(file_ptr->logfp)
+                HDfclose(file_ptr->logfp);
+            H5FL_FREE(H5FD_splitter_t, file_ptr);
+        }
+    } /* end if error */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_open() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_close
+ *
+ * Purpose:     Closes files on both read-write and write-only channels.
+ *
+ * Return:      Success:    SUCCEED
+ *              Failure:    FAIL, file not closed.
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_close(H5FD_t *_file)
+{
+    H5FD_splitter_t *file      = (H5FD_splitter_t *)_file;
+    herr_t           ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Sanity check */
+    HDassert(file);
+
+    if(H5I_dec_ref(file->fa.rw_fapl_id) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_ARGS, FAIL, "can't close R/W FAPL")
+    if(H5I_dec_ref(file->fa.wo_fapl_id) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_ARGS, FAIL, "can't close W/O FAPL")
+
+    if(file->rw_file)
+        if(H5FD_close(file->rw_file) == FAIL)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTCLOSEFILE, FAIL, "unable to close R/W file")
+    if(file->wo_file)
+        if(H5FD_close(file->wo_file) == FAIL)
+            H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTCLOSEFILE, FAIL, "unable to close W/O file")
+
+    if(file->logfp) {
+        HDfclose(file->logfp);
+        file->logfp = NULL;
+    }
+
+    /* Release the file info */
+    file = H5FL_FREE(H5FD_splitter_t, file);
+    file = NULL;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_close() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_get_eoa
+ *
+ * Purpose:     Returns the end-of-address marker for the file. The EOA
+ *              marker is the first address past the last byte allocated in
+ *              the format address space.
+ *
+ * Return:      Success:    The end-of-address-marker
+ *
+ *              Failure:    HADDR_UNDEF
+ *-------------------------------------------------------------------------
+ */
+static haddr_t
+H5FD__splitter_get_eoa(const H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type)
+{
+    const H5FD_splitter_t *file      = (const H5FD_splitter_t *)_file;
+    haddr_t                ret_value = HADDR_UNDEF;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Sanity check */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    if((ret_value = H5FD_get_eoa(file->rw_file, type)) == HADDR_UNDEF)
+        HGOTO_ERROR(H5E_VFL, H5E_BADVALUE, HADDR_UNDEF, "unable to get eoa")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_get_eoa */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_set_eoa
+ *
+ * Purpose:     Set the end-of-address marker for the file. This function is
+ *              called shortly after an existing HDF5 file is opened in order
+ *              to tell the driver where the end of the HDF5 data is located.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_set_eoa(H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type, haddr_t addr)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;
+    herr_t      ret_value = SUCCEED;                /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC)
+
+    /* Sanity check */
+    HDassert(file);
+    HDassert(file->rw_file);
+    HDassert(file->wo_file);
+
+    if(H5FD_set_eoa(file->rw_file, type, addr) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTSET, FAIL, "H5FDset_eoa failed for R/W file")
+
+    if(H5FD_set_eoa(file->wo_file, type, addr) < 0)
+       H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTSET, FAIL, "unable to set EOA for W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_set_eoa() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_get_eof
+ *
+ * Purpose:     Returns the end-of-address marker for the file. The EOA
+ *              marker is the first address past the last byte allocated in
+ *              the format address space.
+ *
+ * Return:      Success:    The end-of-address-marker
+ *
+ *              Failure:    HADDR_UNDEF
+ *-------------------------------------------------------------------------
+ */
+static haddr_t
+H5FD__splitter_get_eof(const H5FD_t *_file, H5FD_mem_t H5_ATTR_UNUSED type)
+{
+    const H5FD_splitter_t *file = (const H5FD_splitter_t *)_file;
+    haddr_t ret_value = HADDR_UNDEF;        /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Sanity check */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    if(HADDR_UNDEF == (ret_value = H5FD_get_eof(file->rw_file, type)))
+        HGOTO_ERROR(H5E_VFL, H5E_CANTGET, HADDR_UNDEF, "unable to get eof")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_get_eof */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_truncate
+ *
+ * Purpose:     Notify driver to truncate the file back to the allocated size.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_truncate(H5FD_t *_file, hid_t dxpl_id, hbool_t closing)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;
+    herr_t           ret_value = SUCCEED;       /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    HDassert(file);
+    HDassert(file->rw_file);
+    HDassert(file->wo_file);
+
+    if(H5FDtruncate(file->rw_file, dxpl_id, closing) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTUPDATE, FAIL, "unable to truncate R/W file")
+
+    if(H5FDtruncate(file->wo_file, dxpl_id, closing) < 0)
+       H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTUPDATE, FAIL, "unable to truncate W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_truncate */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_sb_size
+ *
+ * Purpose:     Obtains the number of bytes required to store the driver file
+ *              access data in the HDF5 superblock.
+ *
+ * Return:      Success:    Number of bytes required.
+ *
+ *              Failure:    0 if an error occurs or if the driver has no
+ *                          data to store in the superblock.
+ *
+ * NOTE: no public API for H5FD_sb_size, it needs to be added
+ *-------------------------------------------------------------------------
+ */
+static hsize_t
+H5FD__splitter_sb_size(H5FD_t *_file)
+{
+    H5FD_splitter_t *file      = (H5FD_splitter_t *)_file;
+    hsize_t          ret_value = 0;
+
+    FUNC_ENTER_STATIC_NOERR
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Sanity check */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    if(file->rw_file)
+        ret_value = H5FD_sb_size(file->rw_file);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_sb_size */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_sb_encode
+ *
+ * Purpose:     Encode driver-specific data into the output arguments.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_sb_encode(H5FD_t *_file, char *name/*out*/, unsigned char *buf/*out*/)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;
+    herr_t           ret_value = SUCCEED;       /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Sanity check */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    if(file->rw_file && H5FD_sb_encode(file->rw_file, name, buf) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTENCODE, FAIL, "unable to encode the superblock in R/W file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_sb_encode */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_sb_decode
+ *
+ * Purpose:     Decodes the driver information block.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ * NOTE: no public API for H5FD_sb_size, need to add
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_sb_decode(H5FD_t *_file, const char *name, const unsigned char *buf)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;
+    herr_t           ret_value = SUCCEED;       /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Sanity check */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    if(H5FD_sb_load(file->rw_file, name, buf) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTDECODE, FAIL, "unable to decode the superblock in R/W file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_sb_decode */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_cmp
+ *
+ * Purpose:     Compare the keys of two files.
+ *
+ * Return:      Success:    A value like strcmp()
+ *              Failure:    Must never fail
+ *-------------------------------------------------------------------------
+ */
+static int
+H5FD__splitter_cmp(const H5FD_t *_f1, const H5FD_t *_f2)
+{
+    const H5FD_splitter_t  *f1 = (const H5FD_splitter_t *)_f1;
+    const H5FD_splitter_t  *f2 = (const H5FD_splitter_t *)_f2;
+    herr_t ret_value = 0;   /* Return value */
+
+    FUNC_ENTER_STATIC_NOERR
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    HDassert(f1);
+    HDassert(f2);
+
+    ret_value = H5FD_cmp(f1->rw_file, f2->rw_file);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_cmp */
+
+
+/*--------------------------------------------------------------------------
+ * Function:    H5FD__splitter_get_handle
+ *
+ * Purpose:     Returns a pointer to the file handle of low-level virtual
+ *              file driver.
+ *
+ * Return:      SUCCEED/FAIL
+ *--------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_get_handle(H5FD_t *_file, hid_t H5_ATTR_UNUSED fapl,
+    void **file_handle)
+{
+    H5FD_splitter_t  *file = (H5FD_splitter_t*)_file;
+    herr_t ret_value = SUCCEED;   /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(file);
+    HDassert(file->rw_file);
+    HDassert(file_handle);
+
+    /* Only do for R/W channel */
+    if(H5FD_get_vfd_handle(file->rw_file, file->fa.rw_fapl_id, file_handle) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTGET, FAIL, "unable to get handle of R/W file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_get_handle */
+
+
+/*--------------------------------------------------------------------------
+ * Function:    H5FD__splitter_lock
+ *
+ * Purpose:     Sets a file lock.
+ *
+ * Return:      SUCCEED/FAIL
+ *--------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_lock(H5FD_t *_file, hbool_t rw)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;   /* VFD file struct */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    /* Place the lock on each file */
+    if(H5FD_lock(file->rw_file, rw) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTLOCKFILE, FAIL, "unable to lock R/W file")
+
+    if(file->wo_file != NULL)
+        if(H5FD_lock(file->wo_file, rw) < 0)
+            H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTLOCKFILE, FAIL, "unable to lock W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_lock */
+
+
+/*--------------------------------------------------------------------------
+ * Function:    H5FD__splitter_unlock
+ *
+ * Purpose:     Removes a file lock.
+ *
+ * Return:      SUCCEED/FAIL
+ *--------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_unlock(H5FD_t *_file)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;   /* VFD file struct */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    /* Remove the lock on each file */
+    if(H5FD_unlock(file->rw_file) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock R/W file")
+
+    if(file->wo_file != NULL)
+        if(H5FD_unlock(file->wo_file) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTUNLOCKFILE, FAIL, "unable to unlock W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_unlock */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_query
+ *
+ * Purpose:     Set the flags that this VFL driver is capable of supporting.
+ *              (listed in H5FDpublic.h)
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_query(const H5FD_t *_file, unsigned long *flags /* out */)
+{
+    const H5FD_splitter_t *file      = (const H5FD_splitter_t *)_file;
+    herr_t                 ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    if(file) {
+        HDassert(file);
+        HDassert(file->rw_file);
+
+        if(H5FDquery(file->rw_file, flags) < 0)
+            HGOTO_ERROR(H5E_VFL, H5E_CANTLOCK, FAIL, "unable to query R/W file");
+    }
+    else {
+        /* There is no file. Because this is a pure passthrough VFD,
+         * it has no features of its own.
+         */
+        if(flags)
+            *flags = 0;
+    }
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_query() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_alloc
+ *
+ * Purpose:     Allocate file memory.
+ *
+ * Return:      Address of allocated space (HADDR_UNDEF if error).
+ *-------------------------------------------------------------------------
+ */
+static haddr_t
+H5FD__splitter_alloc(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, hsize_t size)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;   /* VFD file struct */
+    haddr_t ret_value = HADDR_UNDEF;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    /* Allocate memory for each file, only return the return value for R/W file. */
+    if((ret_value = H5FDalloc(file->rw_file, type, dxpl_id, size)) == HADDR_UNDEF)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTINIT, HADDR_UNDEF, "unable to allocate for R/W file")
+
+    if(H5FDalloc(file->wo_file, type, dxpl_id, size) == HADDR_UNDEF)
+       H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTINIT, HADDR_UNDEF, "unable to alloc for W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_alloc() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_get_type_map
+ *
+ * Purpose:     Retrieve the memory type mapping for this file
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_get_type_map(const H5FD_t *_file, H5FD_mem_t *type_map)
+{
+    const H5FD_splitter_t *file      = (const H5FD_splitter_t *)_file;
+    herr_t                 ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    /* Retrieve memory type mapping for R/W channel only */
+    if(H5FD_get_fs_type_map(file->rw_file, type_map) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTGET, FAIL, "unable to allocate for R/W file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_get_type_map() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_free
+ *
+ * Purpose:     Free the resources for the splitter VFD.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_free(H5FD_t *_file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, hsize_t size)
+{
+    H5FD_splitter_t *file = (H5FD_splitter_t *)_file;   /* VFD file struct */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(file);
+    HDassert(file->rw_file);
+
+    if(H5FDfree(file->rw_file, type, dxpl_id, addr, size) < 0)
+        HGOTO_ERROR(H5E_VFL, H5E_CANTFREE, FAIL, "unable to free for R/W file")
+
+    if(H5FDfree(file->wo_file, type, dxpl_id, addr, size) < 0)
+       H5FD_SPLITTER_WO_ERROR(file, FUNC, H5E_VFL, H5E_CANTINIT, FAIL, "unable to free for W/O file")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_free() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:    H5FD__splitter_log_error
+ *
+ * Purpose:     Log an error from the W/O channel appropriately.
+ *
+ * Return:      SUCCEED/FAIL
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5FD__splitter_log_error(const H5FD_splitter_t *file, const char *atfunc, const char *msg)
+{
+    herr_t ret_value = SUCCEED;
+
+    FUNC_ENTER_STATIC_NOERR
+
+    H5FD_SPLITTER_LOG_CALL(FUNC);
+
+    /* Check arguments */
+    HDassert(file);
+    HDassert(atfunc && *atfunc);
+    HDassert(msg && *msg);
+
+    if(file->logfp != NULL) {
+        size_t size;
+        char  *s;
+
+        size = HDstrlen(atfunc) + HDstrlen(msg) + 3; /* ':', ' ', '\n' */
+        s = (char *)HDmalloc(sizeof(char) * (size + 1));
+        if(NULL == s)
+            ret_value = FAIL;
+        else if(size < (size_t)HDsnprintf(s, size+1, "%s: %s\n", atfunc, msg))
+            ret_value = FAIL;
+        else if(size != HDfwrite(s, 1, size, file->logfp))
+            ret_value = FAIL;
+        HDfree(s);
+    }
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5FD__splitter_log_error() */
+
diff --git a/src/H5FDsplitter.h b/src/H5FDsplitter.h
new file mode 100644
index 0000000..5a5ef29
--- /dev/null
+++ b/src/H5FDsplitter.h
@@ -0,0 +1,99 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://support.hdfgroup.org/ftp/HDF5/releases.  *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*
+ * Purpose:	The public header file for the "splitter" driver.
+ */
+
+#ifndef H5FDsplitter_H
+#define H5FDsplitter_H
+
+#define H5FD_SPLITTER (H5FD_splitter_init())
+
+/* The version of the H5FD_splitter_vfd_config_t structure used */
+#define H5FD_CURR_SPLITTER_VFD_CONFIG_VERSION 1
+
+/* Maximum length of a filename/path string in the Write-Only channel,
+ * including the NULL-terminator.
+ */
+#define H5FD_SPLITTER_PATH_MAX 4096
+
+/* Semi-unique constant used to help identify structure pointers */
+#define H5FD_SPLITTER_MAGIC 0x2B916880
+
+/* ----------------------------------------------------------------------------
+ * Structure:   H5FD_spliiter_vfd_config_t
+ *
+ * One-stop shopping for configuring a Splitter VFD (rather than many
+ * paramaters passed into H5Pset/get functions).
+ *
+ * magic (int32_t)
+ *      Semi-unique number, used to sanity-check that a given pointer is
+ *      likely (or not) to be this structure type. MUST be first.
+ *      If magic is not H5FD_SPLITTER_MAGIC, the structure (and/or pointer to)
+ *      must be considered invalid.
+ *
+ * version (unsigned int)
+ *      Version number of this structure -- informs component membership.
+ *      If not H5FD_CURR_SPLITTER_VFD_CONFIG_VERSION, the structure (and/or
+ *      pointer to) must be considered invalid.
+ *
+ * rw_fapl_id (hid_t)
+ *      Library-given identification number of the Read/Write channel driver
+ *      File Access Property List.
+ *      The driver must support read/write access.
+ *      Must be set to H5P_DEFAULT or a valid FAPL ID.
+ *
+ * wo_fapl_id (hid_t)
+ *      Library-given identification number of the Read/Write channel driver
+ *      File Access Property List.
+ *      The driver feature flags must include H5FD_FEAT_DEFAULT_VFD_COMPAITBLE.
+ *      Must be set to H5P_DEFAULT or a valid FAPL ID.
+ *
+ * wo_file_path (char[H5FD_SPLITTER_PATH_MAX + 1])
+ *      String buffer for the Write-Only channel target file.
+ *      Must be null-terminated, cannot be empty.
+ *
+ * log_file_path (char[H5FD_SPLITTER_PATH_MAX + 1])
+ *      String buffer for the Splitter VFD logging output.
+ *      Must be null-terminated.
+ *      If null, no logfile is created.
+ *
+ * ignore_wo_errors (hbool_t)
+ *      Toggle flag for how judiciously to respond to errors on the Write-Only
+ *      channel.
+ *
+ * ----------------------------------------------------------------------------
+ */
+typedef struct H5FD_splitter_vfd_config_t {
+    int32_t magic;
+    unsigned int version;
+    hid_t rw_fapl_id;
+    hid_t wo_fapl_id;
+    char wo_path[H5FD_SPLITTER_PATH_MAX + 1];
+    char log_file_path[H5FD_SPLITTER_PATH_MAX + 1];
+    hbool_t ignore_wo_errs;
+} H5FD_splitter_vfd_config_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+H5_DLL hid_t H5FD_splitter_init(void);
+H5_DLL herr_t H5Pset_fapl_splitter(hid_t fapl_id, H5FD_splitter_vfd_config_t *config_ptr);
+H5_DLL herr_t H5Pget_fapl_splitter(hid_t fapl_id, H5FD_splitter_vfd_config_t *config_ptr);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+
diff --git a/src/Makefile.am b/src/Makefile.am
index 0ec6c41..a077a19 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -63,7 +63,8 @@ libhdf5_la_SOURCES= H5.c H5checksum.c H5dbg.c H5system.c H5timer.c H5trace.c \
         H5FA.c H5FAcache.c H5FAdbg.c H5FAdblock.c H5FAdblkpage.c H5FAhdr.c \
         H5FAint.c H5FAstat.c H5FAtest.c \
         H5FD.c H5FDcore.c H5FDfamily.c H5FDhdfs.c H5FDint.c H5FDlog.c \
-        H5FDmulti.c H5FDsec2.c H5FDspace.c H5FDstdio.c H5FDtest.c \
+        H5FDmulti.c H5FDsec2.c H5FDspace.c \
+        H5FDsplitter.c H5FDstdio.c H5FDtest.c \
         H5FL.c H5FO.c H5FS.c H5FScache.c H5FSdbg.c H5FSint.c H5FSsection.c \
         H5FSstat.c H5FStest.c \
         H5G.c H5Gbtree2.c H5Gcache.c \
@@ -138,7 +139,7 @@ include_HEADERS = hdf5.h H5api_adpt.h H5overflow.h H5pubconf.h H5public.h H5vers
         H5Epubgen.h H5Epublic.h H5Fpublic.h \
         H5FDpublic.h H5FDcore.h H5FDdirect.h H5FDfamily.h H5FDhdfs.h \
         H5FDlog.h H5FDmpi.h H5FDmpio.h H5FDmulti.h H5FDros3.h \
-        H5FDsec2.h H5FDstdio.h H5FDwindows.h \
+        H5FDsec2.h H5FDsplitter.h H5FDstdio.h H5FDwindows.h \
         H5Gpublic.h  H5Ipublic.h H5Lpublic.h \
         H5MMpublic.h H5Opublic.h H5Ppublic.h \
         H5PLextern.h H5PLpublic.h \
diff --git a/src/hdf5.h b/src/hdf5.h
index f5ded15..9a0ea40 100644
--- a/src/hdf5.h
+++ b/src/hdf5.h
@@ -48,6 +48,7 @@
 #include "H5FDmulti.h"          /* Usage-partitioned file family            */
 #include "H5FDros3.h"           /* R/O S3 "file" I/O                        */
 #include "H5FDsec2.h"           /* POSIX unbuffered file I/O                */
+#include "H5FDsplitter.h"       /* Twin-channel (R/W & R/O) I/O passthrough */
 #include "H5FDstdio.h"          /* Standard C buffered I/O                  */
 #ifdef H5_HAVE_WINDOWS
 #include "H5FDwindows.h"        /* Win32 I/O                                */