bpo-41625: Expose the splice() system call in the os module (GH-21947)

Doc/library/os.rst

@@ -1419,6 +1419,38 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    .. versionadded:: 3.3
 
 
+.. function:: splice(src, dst, count, offset_src=None, offset_dst=None)
+
+   Transfer *count* bytes from file descriptor *src*, starting from offset
+   *offset_src*, to file descriptor *dst*, starting from offset *offset_dst*.
+   At least one of the file descriptors must refer to a pipe. If *offset_src*
+   is None, then *src* is read from the current position; respectively for
+   *offset_dst*. The offset associated to the file descriptor that refers to a
+   pipe must be ``None``. The files pointed by *src* and *dst* must reside in
+   the same filesystem, otherwise an :exc:`OSError` is raised with
+   :attr:`~OSError.errno` set to :data:`errno.EXDEV`.
+
+   This copy is done without the additional cost of transferring data
+   from the kernel to user space and then back into the kernel. Additionally,
+   some filesystems could implement extra optimizations. The copy is done as if
+   both files are opened as binary.
+
+   Upon successful completion, returns the number of bytes spliced to or from
+   the pipe. A return value of 0 means end of input. If *src* refers to a
+   pipe, then this means that there was no data to transfer, and it would not
+   make sense to block because there are no writers connected to the write end
+   of the pipe.
+
+   .. availability:: Linux kernel >= 2.6.17 or glibc >= 2.5
+
+   .. versionadded:: 3.10
+
+
+.. data:: SPLICE_F_MOVE
+          SPLICE_F_NONBLOCK
+          SPLICE_F_MORE
+
+
 .. function:: readv(fd, buffers)
 
    Read from a file descriptor *fd* into a number of mutable :term:`bytes-like

Doc/whatsnew/3.10.rst

@@ -233,6 +233,11 @@ Added a new function :func:`os.eventfd` and related helpers to wrap the
 ``eventfd2`` syscall on Linux.
 (Contributed by Christian Heimes in :issue:`41001`.)
 
+Added :func:`os.splice()` that allows to move data between two file
+descriptors without copying between kernel address space and user
+address space, where one of the file descriptors must refer to a
+pipe. (Contributed by Pablo Galindo in :issue:`41625`.)
+
 py_compile
 ----------
 

Lib/test/test_os.py

@@ -381,6 +381,123 @@ class FileTests(unittest.TestCase):
             self.assertEqual(read[out_seek:],
                              data[in_skip:in_skip+i])
 
+    @unittest.skipUnless(hasattr(os, 'splice'), 'test needs os.splice()')
+    def test_splice_invalid_values(self):
+        with self.assertRaises(ValueError):
+            os.splice(0, 1, -10)
+
+    @unittest.skipUnless(hasattr(os, 'splice'), 'test needs os.splice()')
+    def test_splice(self):
+        TESTFN2 = os_helper.TESTFN + ".3"
+        data = b'0123456789'
+
+        create_file(os_helper.TESTFN, data)
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+
+        in_file = open(os_helper.TESTFN, 'rb')
+        self.addCleanup(in_file.close)
+        in_fd = in_file.fileno()
+
+        read_fd, write_fd = os.pipe()
+        self.addCleanup(lambda: os.close(read_fd))
+        self.addCleanup(lambda: os.close(write_fd))
+
+        try:
+            i = os.splice(in_fd, write_fd, 5)
+        except OSError as e:
+            # Handle the case in which Python was compiled
+            # in a system with the syscall but without support
+            # in the kernel.
+            if e.errno != errno.ENOSYS:
+                raise
+            self.skipTest(e)
+        else:
+            # The number of copied bytes can be less than
+            # the number of bytes originally requested.
+            self.assertIn(i, range(0, 6));
+
+            self.assertEqual(os.read(read_fd, 100), data[:i])
+
+    @unittest.skipUnless(hasattr(os, 'splice'), 'test needs os.splice()')
+    def test_splice_offset_in(self):
+        TESTFN4 = os_helper.TESTFN + ".4"
+        data = b'0123456789'
+        bytes_to_copy = 6
+        in_skip = 3
+
+        create_file(os_helper.TESTFN, data)
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+
+        in_file = open(os_helper.TESTFN, 'rb')
+        self.addCleanup(in_file.close)
+        in_fd = in_file.fileno()
+
+        read_fd, write_fd = os.pipe()
+        self.addCleanup(lambda: os.close(read_fd))
+        self.addCleanup(lambda: os.close(write_fd))
+
+        try:
+            i = os.splice(in_fd, write_fd, bytes_to_copy, offset_src=in_skip)
+        except OSError as e:
+            # Handle the case in which Python was compiled
+            # in a system with the syscall but without support
+            # in the kernel.
+            if e.errno != errno.ENOSYS:
+                raise
+            self.skipTest(e)
+        else:
+            # The number of copied bytes can be less than
+            # the number of bytes originally requested.
+            self.assertIn(i, range(0, bytes_to_copy+1));
+
+            read = os.read(read_fd, 100)
+            # 012 are skipped (in_skip)
+            # 345678 are copied in the file (in_skip + bytes_to_copy)
+            self.assertEqual(read, data[in_skip:in_skip+i])
+
+    @unittest.skipUnless(hasattr(os, 'splice'), 'test needs os.splice()')
+    def test_splice_offset_out(self):
+        TESTFN4 = os_helper.TESTFN + ".4"
+        data = b'0123456789'
+        bytes_to_copy = 6
+        out_seek = 3
+
+        create_file(os_helper.TESTFN, data)
+        self.addCleanup(os_helper.unlink, os_helper.TESTFN)
+
+        read_fd, write_fd = os.pipe()
+        self.addCleanup(lambda: os.close(read_fd))
+        self.addCleanup(lambda: os.close(write_fd))
+        os.write(write_fd, data)
+
+        out_file = open(TESTFN4, 'w+b')
+        self.addCleanup(os_helper.unlink, TESTFN4)
+        self.addCleanup(out_file.close)
+        out_fd = out_file.fileno()
+
+        try:
+            i = os.splice(read_fd, out_fd, bytes_to_copy, offset_dst=out_seek)
+        except OSError as e:
+            # Handle the case in which Python was compiled
+            # in a system with the syscall but without support
+            # in the kernel.
+            if e.errno != errno.ENOSYS:
+                raise
+            self.skipTest(e)
+        else:
+            # The number of copied bytes can be less than
+            # the number of bytes originally requested.
+            self.assertIn(i, range(0, bytes_to_copy+1));
+
+            with open(TESTFN4, 'rb') as in_file:
+                read = in_file.read()
+            # seeked bytes (5) are zero'ed
+            self.assertEqual(read[:out_seek], b'\x00'*out_seek)
+            # 012 are skipped (in_skip)
+            # 345678 are copied in the file (in_skip + bytes_to_copy)
+            self.assertEqual(read[out_seek:], data[:i])
+
+
 # Test attributes on return values from os.*stat* family.
 class StatAttributeTests(unittest.TestCase):
     def setUp(self):

Misc/NEWS.d/next/Library/2020-08-24-16-59-04.bpo-41625.Cc967V.rst

@@ -0,0 +1,2 @@
+Expose the :c:func:`splice` as :func:`os.splice` in the :mod:`os` module.
+Patch by Pablo Galindo

Modules/clinic/posixmodule.c.h

@@ -5674,6 +5674,106 @@ exit:
 
 #endif /* defined(HAVE_COPY_FILE_RANGE) */
 
+#if defined(HAVE_SPLICE)
+
+PyDoc_STRVAR(os_splice__doc__,
+"splice($module, /, src, dst, count, offset_src=None, offset_dst=None,\n"
+"       flags=0)\n"
+"--\n"
+"\n"
+"Transfer count bytes from one pipe to a descriptor or vice versa.\n"
+"\n"
+"  src\n"
+"    Source file descriptor.\n"
+"  dst\n"
+"    Destination file descriptor.\n"
+"  count\n"
+"    Number of bytes to copy.\n"
+"  offset_src\n"
+"    Starting offset in src.\n"
+"  offset_dst\n"
+"    Starting offset in dst.\n"
+"  flags\n"
+"    Flags to modify the semantics of the call.\n"
+"\n"
+"If offset_src is None, then src is read from the current position;\n"
+"respectively for offset_dst. The offset associated to the file\n"
+"descriptor that refers to a pipe must be None.");
+
+#define OS_SPLICE_METHODDEF    \
+    {"splice", (PyCFunction)(void(*)(void))os_splice, METH_FASTCALL|METH_KEYWORDS, os_splice__doc__},
+
+static PyObject *
+os_splice_impl(PyObject *module, int src, int dst, Py_ssize_t count,
+               PyObject *offset_src, PyObject *offset_dst,
+               unsigned int flags);
+
+static PyObject *
+os_splice(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"src", "dst", "count", "offset_src", "offset_dst", "flags", NULL};
+    static _PyArg_Parser _parser = {NULL, _keywords, "splice", 0};
+    PyObject *argsbuf[6];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 3;
+    int src;
+    int dst;
+    Py_ssize_t count;
+    PyObject *offset_src = Py_None;
+    PyObject *offset_dst = Py_None;
+    unsigned int flags = 0;
+
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 3, 6, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    src = _PyLong_AsInt(args[0]);
+    if (src == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    dst = _PyLong_AsInt(args[1]);
+    if (dst == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        count = ival;
+    }
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[3]) {
+        offset_src = args[3];
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    if (args[4]) {
+        offset_dst = args[4];
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    if (!_PyLong_UnsignedInt_Converter(args[5], &flags)) {
+        goto exit;
+    }
+skip_optional_pos:
+    return_value = os_splice_impl(module, src, dst, count, offset_src, offset_dst, flags);
+
+exit:
+    return return_value;
+}
+
+#endif /* defined(HAVE_SPLICE) */
+
 #if defined(HAVE_MKFIFO)
 
 PyDoc_STRVAR(os_mkfifo__doc__,
@@ -8864,6 +8964,10 @@ exit:
     #define OS_COPY_FILE_RANGE_METHODDEF
 #endif /* !defined(OS_COPY_FILE_RANGE_METHODDEF) */
 
+#ifndef OS_SPLICE_METHODDEF
+    #define OS_SPLICE_METHODDEF
+#endif /* !defined(OS_SPLICE_METHODDEF) */
+
 #ifndef OS_MKFIFO_METHODDEF
     #define OS_MKFIFO_METHODDEF
 #endif /* !defined(OS_MKFIFO_METHODDEF) */
@@ -9059,4 +9163,4 @@ exit:
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=49b7ed768242ef7c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=8a59e91178897267 input=a9049054013a1b77]*/

Modules/posixmodule.c

@@ -6521,7 +6521,6 @@ os_spawnve_impl(PyObject *module, int mode, path_t *path, PyObject *argv,
 
 #endif /* HAVE_SPAWNV */
 
-
 #ifdef HAVE_FORK
 
 /* Helper function to validate arguments.
@@ -10370,6 +10369,75 @@ os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
 }
 #endif /* HAVE_COPY_FILE_RANGE*/
 
+#ifdef HAVE_SPLICE
+/*[clinic input]
+
+os.splice
+    src: int
+        Source file descriptor.
+    dst: int
+        Destination file descriptor.
+    count: Py_ssize_t
+        Number of bytes to copy.
+    offset_src: object = None
+        Starting offset in src.
+    offset_dst: object = None
+        Starting offset in dst.
+    flags: unsigned_int = 0
+        Flags to modify the semantics of the call.
+
+Transfer count bytes from one pipe to a descriptor or vice versa.
+
+If offset_src is None, then src is read from the current position;
+respectively for offset_dst. The offset associated to the file
+descriptor that refers to a pipe must be None.
+[clinic start generated code]*/
+
+static PyObject *
+os_splice_impl(PyObject *module, int src, int dst, Py_ssize_t count,
+               PyObject *offset_src, PyObject *offset_dst,
+               unsigned int flags)
+/*[clinic end generated code: output=d0386f25a8519dc5 input=047527c66c6d2e0a]*/
+{
+    off_t offset_src_val, offset_dst_val;
+    off_t *p_offset_src = NULL;
+    off_t *p_offset_dst = NULL;
+    Py_ssize_t ret;
+    int async_err = 0;
+
+    if (count < 0) {
+        PyErr_SetString(PyExc_ValueError, "negative value for 'count' not allowed");
+        return NULL;
+    }
+
+    if (offset_src != Py_None) {
+        if (!Py_off_t_converter(offset_src, &offset_src_val)) {
+            return NULL;
+        }
+        p_offset_src = &offset_src_val;
+    }
+
+    if (offset_dst != Py_None) {
+        if (!Py_off_t_converter(offset_dst, &offset_dst_val)) {
+            return NULL;
+        }
+        p_offset_dst = &offset_dst_val;
+    }
+
+    do {
+        Py_BEGIN_ALLOW_THREADS
+        ret = splice(src, p_offset_src, dst, p_offset_dst, count, flags);
+        Py_END_ALLOW_THREADS
+    } while (ret < 0 && errno == EINTR && !(async_err = PyErr_CheckSignals()));
+
+    if (ret < 0) {
+        return (!async_err) ? posix_error() : NULL;
+    }
+
+    return PyLong_FromSsize_t(ret);
+}
+#endif /* HAVE_SPLICE*/
+
 #ifdef HAVE_MKFIFO
 /*[clinic input]
 os.mkfifo
@@ -14550,6 +14618,7 @@ static PyMethodDef posix_methods[] = {
     OS_POSIX_SPAWNP_METHODDEF
     OS_READLINK_METHODDEF
     OS_COPY_FILE_RANGE_METHODDEF
+    OS_SPLICE_METHODDEF
     OS_RENAME_METHODDEF
     OS_REPLACE_METHODDEF
     OS_RMDIR_METHODDEF
@@ -15072,6 +15141,13 @@ all_ins(PyObject *m)
     if (PyModule_AddIntConstant(m, "RWF_APPEND", RWF_APPEND)) return -1;
 #endif
 
+/* constants for splice */
+#ifdef HAVE_SPLICE
+    if (PyModule_AddIntConstant(m, "SPLICE_F_MOVE", SPLICE_F_MOVE)) return -1;
+    if (PyModule_AddIntConstant(m, "SPLICE_F_NONBLOCK", SPLICE_F_NONBLOCK)) return -1;
+    if (PyModule_AddIntConstant(m, "SPLICE_F_MORE", SPLICE_F_MORE)) return -1;
+#endif
+
 /* constants for posix_spawn */
 #ifdef HAVE_POSIX_SPAWN
     if (PyModule_AddIntConstant(m, "POSIX_SPAWN_OPEN", POSIX_SPAWN_OPEN)) return -1;

aclocal.m4

@@ -67,7 +67,7 @@ AS_VAR_POPDEF([CACHEVAR])dnl
 ])dnl AX_CHECK_COMPILE_FLAGS
 
 # pkg.m4 - Macros to locate and utilise pkg-config.   -*- Autoconf -*-
-# serial 11 (pkg-config-0.29.1)
+# serial 12 (pkg-config-0.29.2)
 
 dnl Copyright © 2004 Scott James Remnant <scott@netsplit.com>.
 dnl Copyright © 2012-2015 Dan Nicholson <dbn.lists@gmail.com>
@@ -109,7 +109,7 @@ dnl
 dnl See the "Since" comment for each macro you use to see what version
 dnl of the macros you require.
 m4_defun([PKG_PREREQ],
-[m4_define([PKG_MACROS_VERSION], [0.29.1])
+[m4_define([PKG_MACROS_VERSION], [0.29.2])
 m4_if(m4_version_compare(PKG_MACROS_VERSION, [$1]), -1,
     [m4_fatal([pkg.m4 version $1 or higher is required but ]PKG_MACROS_VERSION[ found])])
 ])dnl PKG_PREREQ
@@ -210,7 +210,7 @@ AC_ARG_VAR([$1][_CFLAGS], [C compiler flags for $1, overriding pkg-config])dnl
 AC_ARG_VAR([$1][_LIBS], [linker flags for $1, overriding pkg-config])dnl
 
 pkg_failed=no
-AC_MSG_CHECKING([for $1])
+AC_MSG_CHECKING([for $2])
 
 _PKG_CONFIG([$1][_CFLAGS], [cflags], [$2])
 _PKG_CONFIG([$1][_LIBS], [libs], [$2])
@@ -220,7 +220,7 @@ and $1[]_LIBS to avoid the need to call pkg-config.
 See the pkg-config man page for more details.])
 
 if test $pkg_failed = yes; then
-   	AC_MSG_RESULT([no])
+        AC_MSG_RESULT([no])
         _PKG_SHORT_ERRORS_SUPPORTED
         if test $_pkg_short_errors_supported = yes; then
 	        $1[]_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "$2" 2>&1`
@@ -241,7 +241,7 @@ installed software in a non-standard prefix.
 _PKG_TEXT])[]dnl
         ])
 elif test $pkg_failed = untried; then
-     	AC_MSG_RESULT([no])
+        AC_MSG_RESULT([no])
 	m4_default([$4], [AC_MSG_FAILURE(
 [The pkg-config script could not be found or is too old.  Make sure it
 is in your PATH or set the PKG_CONFIG environment variable to the full
@@ -342,73 +342,5 @@ AS_VAR_COPY([$1], [pkg_cv_][$1])
 AS_VAR_IF([$1], [""], [$5], [$4])dnl
 ])dnl PKG_CHECK_VAR
 
-dnl PKG_WITH_MODULES(VARIABLE-PREFIX, MODULES,
-dnl   [ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND],
-dnl   [DESCRIPTION], [DEFAULT])
-dnl ------------------------------------------
-dnl
-dnl Prepare a "--with-" configure option using the lowercase
-dnl [VARIABLE-PREFIX] name, merging the behaviour of AC_ARG_WITH and
-dnl PKG_CHECK_MODULES in a single macro.
-AC_DEFUN([PKG_WITH_MODULES],
-[
-m4_pushdef([with_arg], m4_tolower([$1]))
-
-m4_pushdef([description],
-           [m4_default([$5], [build with ]with_arg[ support])])
-
-m4_pushdef([def_arg], [m4_default([$6], [auto])])
-m4_pushdef([def_action_if_found], [AS_TR_SH([with_]with_arg)=yes])
-m4_pushdef([def_action_if_not_found], [AS_TR_SH([with_]with_arg)=no])
-
-m4_case(def_arg,
-            [yes],[m4_pushdef([with_without], [--without-]with_arg)],
-            [m4_pushdef([with_without],[--with-]with_arg)])
-
-AC_ARG_WITH(with_arg,
-     AS_HELP_STRING(with_without, description[ @<:@default=]def_arg[@:>@]),,
-    [AS_TR_SH([with_]with_arg)=def_arg])
-
-AS_CASE([$AS_TR_SH([with_]with_arg)],
-            [yes],[PKG_CHECK_MODULES([$1],[$2],$3,$4)],
-            [auto],[PKG_CHECK_MODULES([$1],[$2],
-                                        [m4_n([def_action_if_found]) $3],
-                                        [m4_n([def_action_if_not_found]) $4])])
-
-m4_popdef([with_arg])
-m4_popdef([description])
-m4_popdef([def_arg])
-
-])dnl PKG_WITH_MODULES
-
-dnl PKG_HAVE_WITH_MODULES(VARIABLE-PREFIX, MODULES,
-dnl   [DESCRIPTION], [DEFAULT])
-dnl -----------------------------------------------
-dnl
-dnl Convenience macro to trigger AM_CONDITIONAL after PKG_WITH_MODULES
-dnl check._[VARIABLE-PREFIX] is exported as make variable.
-AC_DEFUN([PKG_HAVE_WITH_MODULES],
-[
-PKG_WITH_MODULES([$1],[$2],,,[$3],[$4])
-
-AM_CONDITIONAL([HAVE_][$1],
-               [test "$AS_TR_SH([with_]m4_tolower([$1]))" = "yes"])
-])dnl PKG_HAVE_WITH_MODULES
-
-dnl PKG_HAVE_DEFINE_WITH_MODULES(VARIABLE-PREFIX, MODULES,
-dnl   [DESCRIPTION], [DEFAULT])
-dnl ------------------------------------------------------
-dnl
-dnl Convenience macro to run AM_CONDITIONAL and AC_DEFINE after
-dnl PKG_WITH_MODULES check. HAVE_[VARIABLE-PREFIX] is exported as make
-dnl and preprocessor variable.
-AC_DEFUN([PKG_HAVE_DEFINE_WITH_MODULES],
-[
-PKG_HAVE_WITH_MODULES([$1],[$2],[$3],[$4])
-
-AS_IF([test "$AS_TR_SH([with_]m4_tolower([$1]))" = "yes"],
-        [AC_DEFINE([HAVE_][$1], 1, [Enable ]m4_tolower([$1])[ support])])
-])dnl PKG_HAVE_DEFINE_WITH_MODULES
-
 m4_include([m4/ax_c_float_words_bigendian.m4])
 m4_include([m4/ax_check_openssl.m4])

configure

@@ -11726,7 +11726,7 @@ for ac_func in alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  sched_get_priority_max sched_setaffinity sched_setscheduler sched_setparam \
  sched_rr_get_interval \
  sigaction sigaltstack sigfillset siginterrupt sigpending sigrelse \
- sigtimedwait sigwait sigwaitinfo snprintf strftime strlcpy strsignal symlinkat sync \
+ sigtimedwait sigwait sigwaitinfo snprintf splice strftime strlcpy strsignal symlinkat sync \
  sysconf tcgetpgrp tcsetpgrp tempnam timegm times tmpfile tmpnam tmpnam_r \
  truncate uname unlinkat utimensat utimes vfork waitid waitpid wait3 wait4 \
  wcscoll wcsftime wcsxfrm wmemcmp writev _getpty rtpSpawn

configure.ac

@@ -3684,7 +3684,7 @@ AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
  sched_get_priority_max sched_setaffinity sched_setscheduler sched_setparam \
  sched_rr_get_interval \
  sigaction sigaltstack sigfillset siginterrupt sigpending sigrelse \
- sigtimedwait sigwait sigwaitinfo snprintf strftime strlcpy strsignal symlinkat sync \
+ sigtimedwait sigwait sigwaitinfo snprintf splice strftime strlcpy strsignal symlinkat sync \
  sysconf tcgetpgrp tcsetpgrp tempnam timegm times tmpfile tmpnam tmpnam_r \
  truncate uname unlinkat utimensat utimes vfork waitid waitpid wait3 wait4 \
  wcscoll wcsftime wcsxfrm wmemcmp writev _getpty rtpSpawn)

pyconfig.h.in

@@ -1018,6 +1018,9 @@
 /* Define to 1 if you have the <spawn.h> header file. */
 #undef HAVE_SPAWN_H
 
+/* Define to 1 if you have the `splice' function. */
+#undef HAVE_SPLICE
+
 /* Define if your compiler provides ssize_t */
 #undef HAVE_SSIZE_T