bpo-26826: Expose copy_file_range in the os module (GH-7255)

Doc/library/os.rst

@@ -707,6 +707,28 @@ as internal buffering of data.
               pass
 
 
+.. function:: copy_file_range(src, dst, count, offset_src=None, offset_dst=None)
+
+   Copy *count* bytes from file descriptor *src*, starting from offset
+   *offset_src*, to file descriptor *dst*, starting from offset *offset_dst*.
+   If *offset_src* is None, then *src* is read from the current position;
+   respectively for *offset_dst*. 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.
+
+   The return value is the amount of bytes copied. This could be less than the
+   amount requested.
+
+   .. availability:: Linux kernel >= 4.5 or glibc >= 2.27.
+
+   .. versionadded:: 3.8
+
+
 .. function:: device_encoding(fd)
 
    Return a string describing the encoding of the device associated with *fd*

Lib/test/test_os.py

@@ -231,6 +231,89 @@ class FileTests(unittest.TestCase):
         except (NotImplementedError, OSError):
             pass  # No OS support or unprivileged user
 
+    @unittest.skipUnless(hasattr(os, 'copy_file_range'), 'test needs os.copy_file_range()')
+    def test_copy_file_range_invalid_values(self):
+        with self.assertRaises(ValueError):
+            os.copy_file_range(0, 1, -10)
+
+    @unittest.skipUnless(hasattr(os, 'copy_file_range'), 'test needs os.copy_file_range()')
+    def test_copy_file_range(self):
+        TESTFN2 = support.TESTFN + ".3"
+        data = b'0123456789'
+
+        create_file(support.TESTFN, data)
+        self.addCleanup(support.unlink, support.TESTFN)
+
+        in_file = open(support.TESTFN, 'rb')
+        self.addCleanup(in_file.close)
+        in_fd = in_file.fileno()
+
+        out_file = open(TESTFN2, 'w+b')
+        self.addCleanup(support.unlink, TESTFN2)
+        self.addCleanup(out_file.close)
+        out_fd = out_file.fileno()
+
+        try:
+            i = os.copy_file_range(in_fd, out_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));
+
+            with open(TESTFN2, 'rb') as in_file:
+                self.assertEqual(in_file.read(), data[:i])
+
+    @unittest.skipUnless(hasattr(os, 'copy_file_range'), 'test needs os.copy_file_range()')
+    def test_copy_file_range_offset(self):
+        TESTFN4 = support.TESTFN + ".4"
+        data = b'0123456789'
+        bytes_to_copy = 6
+        in_skip = 3
+        out_seek = 5
+
+        create_file(support.TESTFN, data)
+        self.addCleanup(support.unlink, support.TESTFN)
+
+        in_file = open(support.TESTFN, 'rb')
+        self.addCleanup(in_file.close)
+        in_fd = in_file.fileno()
+
+        out_file = open(TESTFN4, 'w+b')
+        self.addCleanup(support.unlink, TESTFN4)
+        self.addCleanup(out_file.close)
+        out_fd = out_file.fileno()
+
+        try:
+            i = os.copy_file_range(in_fd, out_fd, bytes_to_copy,
+                                   offset_src=in_skip,
+                                   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[in_skip:in_skip+i])
 
 # Test attributes on return values from os.*stat* family.
 class StatAttributeTests(unittest.TestCase):

Misc/NEWS.d/next/Core and Builtins/2018-05-30-23-43-03.bpo-26826.NkRzjb.rst

@@ -0,0 +1 @@
+Expose :func:`copy_file_range` as a low level API in the :mod:`os` module.

Modules/clinic/posixmodule.c.h

@@ -5395,6 +5395,108 @@ exit:
 
 #endif /* (defined(HAVE_PWRITEV) || defined (HAVE_PWRITEV2)) */
 
+#if defined(HAVE_COPY_FILE_RANGE)
+
+PyDoc_STRVAR(os_copy_file_range__doc__,
+"copy_file_range($module, /, src, dst, count, offset_src=None,\n"
+"                offset_dst=None)\n"
+"--\n"
+"\n"
+"Copy count bytes from one file descriptor to another.\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"
+"\n"
+"If offset_src is None, then src is read from the current position;\n"
+"respectively for offset_dst.");
+
+#define OS_COPY_FILE_RANGE_METHODDEF    \
+    {"copy_file_range", (PyCFunction)(void(*)(void))os_copy_file_range, METH_FASTCALL|METH_KEYWORDS, os_copy_file_range__doc__},
+
+static PyObject *
+os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
+                        PyObject *offset_src, PyObject *offset_dst);
+
+static PyObject *
+os_copy_file_range(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", NULL};
+    static _PyArg_Parser _parser = {NULL, _keywords, "copy_file_range", 0};
+    PyObject *argsbuf[5];
+    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;
+
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 3, 5, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (PyFloat_Check(args[0])) {
+        PyErr_SetString(PyExc_TypeError,
+                        "integer argument expected, got float" );
+        goto exit;
+    }
+    src = _PyLong_AsInt(args[0]);
+    if (src == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    if (PyFloat_Check(args[1])) {
+        PyErr_SetString(PyExc_TypeError,
+                        "integer argument expected, got float" );
+        goto exit;
+    }
+    dst = _PyLong_AsInt(args[1]);
+    if (dst == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    if (PyFloat_Check(args[2])) {
+        PyErr_SetString(PyExc_TypeError,
+                        "integer argument expected, got float" );
+        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;
+        }
+    }
+    offset_dst = args[4];
+skip_optional_pos:
+    return_value = os_copy_file_range_impl(module, src, dst, count, offset_src, offset_dst);
+
+exit:
+    return return_value;
+}
+
+#endif /* defined(HAVE_COPY_FILE_RANGE) */
+
 #if defined(HAVE_MKFIFO)
 
 PyDoc_STRVAR(os_mkfifo__doc__,
@@ -8460,6 +8562,10 @@ exit:
     #define OS_PWRITEV_METHODDEF
 #endif /* !defined(OS_PWRITEV_METHODDEF) */
 
+#ifndef OS_COPY_FILE_RANGE_METHODDEF
+    #define OS_COPY_FILE_RANGE_METHODDEF
+#endif /* !defined(OS_COPY_FILE_RANGE_METHODDEF) */
+
 #ifndef OS_MKFIFO_METHODDEF
     #define OS_MKFIFO_METHODDEF
 #endif /* !defined(OS_MKFIFO_METHODDEF) */
@@ -8635,4 +8741,4 @@ exit:
 #ifndef OS__REMOVE_DLL_DIRECTORY_METHODDEF
     #define OS__REMOVE_DLL_DIRECTORY_METHODDEF
 #endif /* !defined(OS__REMOVE_DLL_DIRECTORY_METHODDEF) */
-/*[clinic end generated code: output=855b81aafd05beed input=a9049054013a1b77]*/
+/*[clinic end generated code: output=b3ae8afd275ea5cd input=a9049054013a1b77]*/

Modules/posixmodule.c

@@ -117,6 +117,10 @@ corresponding Unix manual entries for more information on calls.");
 #include <sched.h>
 #endif
 
+#ifdef HAVE_COPY_FILE_RANGE
+#include <unistd.h>
+#endif
+
 #if !defined(CPU_ALLOC) && defined(HAVE_SCHED_SETAFFINITY)
 #undef HAVE_SCHED_SETAFFINITY
 #endif
@@ -9455,8 +9459,74 @@ os_pwritev_impl(PyObject *module, int fd, PyObject *buffers, Py_off_t offset,
 }
 #endif /* HAVE_PWRITEV */
 
+#ifdef HAVE_COPY_FILE_RANGE
+/*[clinic input]
+
+os.copy_file_range
+    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.
+
+Copy count bytes from one file descriptor to another.
+
+If offset_src is None, then src is read from the current position;
+respectively for offset_dst.
+[clinic start generated code]*/
+
+static PyObject *
+os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
+                        PyObject *offset_src, PyObject *offset_dst)
+/*[clinic end generated code: output=1a91713a1d99fc7a input=42fdce72681b25a9]*/
+{
+    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;
+    /* The flags argument is provided to allow
+     * for future extensions and currently must be to 0. */
+    int flags = 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 = copy_file_range(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_COPY_FILE_RANGE*/
 
 #ifdef HAVE_MKFIFO
 /*[clinic input]
@@ -13432,6 +13502,7 @@ static PyMethodDef posix_methods[] = {
     OS_POSIX_SPAWN_METHODDEF
     OS_POSIX_SPAWNP_METHODDEF
     OS_READLINK_METHODDEF
+    OS_COPY_FILE_RANGE_METHODDEF
     OS_RENAME_METHODDEF
     OS_REPLACE_METHODDEF
     OS_RMDIR_METHODDEF

aclocal.m4

@@ -12,9 +12,9 @@
 # PARTICULAR PURPOSE.
 
 m4_ifndef([AC_CONFIG_MACRO_DIRS], [m4_defun([_AM_CONFIG_MACRO_DIRS], [])m4_defun([AC_CONFIG_MACRO_DIRS], [_AM_CONFIG_MACRO_DIRS($@)])])
-dnl pkg.m4 - Macros to locate and utilise pkg-config.   -*- Autoconf -*-
+# pkg.m4 - Macros to locate and utilise pkg-config.   -*- Autoconf -*-
-dnl serial 11 (pkg-config-0.29.1)
+# serial 11 (pkg-config-0.29.1)
-dnl
+
 dnl Copyright © 2004 Scott James Remnant <scott@netsplit.com>.
 dnl Copyright © 2012-2015 Dan Nicholson <dbn.lists@gmail.com>
 dnl
@@ -288,5 +288,73 @@ 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

@@ -785,7 +785,6 @@ infodir
 docdir
 oldincludedir
 includedir
-runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -898,7 +897,6 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
-runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -1151,15 +1149,6 @@ do
   | -silent | --silent | --silen | --sile | --sil)
     silent=yes ;;
 
-  -runstatedir | --runstatedir | --runstatedi | --runstated \
-  | --runstate | --runstat | --runsta | --runst | --runs \
-  | --run | --ru | --r)
-    ac_prev=runstatedir ;;
-  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
-  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
-  | --run=* | --ru=* | --r=*)
-    runstatedir=$ac_optarg ;;
-
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1297,7 +1286,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir runstatedir
+		libdir localedir mandir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -1450,7 +1439,6 @@ Fine tuning of the installation directories:
   --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
   --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
   --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
-  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
   --libdir=DIR            object code libraries [EPREFIX/lib]
   --includedir=DIR        C header files [PREFIX/include]
   --oldincludedir=DIR     C header files for non-gcc [/usr/include]
@@ -11476,7 +11464,8 @@ fi
 
 # checks for library functions
 for ac_func in alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
- clock confstr ctermid dup3 execv explicit_bzero explicit_memset faccessat fchmod fchmodat fchown fchownat \
+ clock confstr copy_file_range ctermid dup3 execv explicit_bzero explicit_memset \
+ faccessat fchmod fchmodat fchown fchownat \
  fexecve fdopendir fork fpathconf fstatat ftime ftruncate futimesat \
  futimens futimes gai_strerror getentropy \
  getgrgid_r getgrnam_r \

configure.ac

@@ -3520,7 +3520,8 @@ fi
 
 # checks for library functions
 AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
- clock confstr ctermid dup3 execv explicit_bzero explicit_memset faccessat fchmod fchmodat fchown fchownat \
+ clock confstr copy_file_range ctermid dup3 execv explicit_bzero explicit_memset \
+ faccessat fchmod fchmodat fchown fchownat \
  fexecve fdopendir fork fpathconf fstatat ftime ftruncate futimesat \
  futimens futimes gai_strerror getentropy \
  getgrgid_r getgrnam_r \

pyconfig.h.in

@@ -148,6 +148,9 @@
 /* Define to 1 if you have the `copysign' function. */
 #undef HAVE_COPYSIGN
 
+/* Define to 1 if you have the `copy_file_range' function. */
+#undef HAVE_COPY_FILE_RANGE
+
 /* Define to 1 if you have the <crypt.h> header file. */
 #undef HAVE_CRYPT_H