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bpo-26826: Expose copy_file_range in the os module (GH-7255)
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Lines changed: 363 additions & 19 deletions

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‎Doc/library/os.rst‎

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@@ -707,6 +707,28 @@ as internal buffering of data.
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pass
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.. function:: copy_file_range(src, dst, count, offset_src=None, offset_dst=None)
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Copy *count* bytes from file descriptor *src*, starting from offset
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*offset_src*, to file descriptor *dst*, starting from offset *offset_dst*.
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If *offset_src* is None, then *src* is read from the current position;
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respectively for *offset_dst*. The files pointed by *src* and *dst*
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must reside in the same filesystem, otherwise an :exc:`OSError` is
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raised with :attr:`~OSError.errno` set to :data:`errno.EXDEV`.
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This copy is done without the additional cost of transferring data
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from the kernel to user space and then back into the kernel. Additionally,
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some filesystems could implement extra optimizations. The copy is done as if
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both files are opened as binary.
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The return value is the amount of bytes copied. This could be less than the
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amount requested.
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.. availability:: Linux kernel >= 4.5 or glibc >= 2.27.
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.. versionadded:: 3.8
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.. function:: device_encoding(fd)
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Return a string describing the encoding of the device associated with *fd*

‎Lib/test/test_os.py‎

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@@ -231,6 +231,89 @@ def test_symlink_keywords(self):
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except (NotImplementedError, OSError):
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pass # No OS support or unprivileged user
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@unittest.skipUnless(hasattr(os, 'copy_file_range'), 'test needs os.copy_file_range()')
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def test_copy_file_range_invalid_values(self):
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with self.assertRaises(ValueError):
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os.copy_file_range(0, 1, -10)
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@unittest.skipUnless(hasattr(os, 'copy_file_range'), 'test needs os.copy_file_range()')
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def test_copy_file_range(self):
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TESTFN2 = support.TESTFN + ".3"
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data = b'0123456789'
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create_file(support.TESTFN, data)
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self.addCleanup(support.unlink, support.TESTFN)
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in_file = open(support.TESTFN, 'rb')
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self.addCleanup(in_file.close)
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in_fd = in_file.fileno()
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out_file = open(TESTFN2, 'w+b')
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self.addCleanup(support.unlink, TESTFN2)
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self.addCleanup(out_file.close)
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out_fd = out_file.fileno()
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try:
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i = os.copy_file_range(in_fd, out_fd, 5)
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except OSError as e:
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# Handle the case in which Python was compiled
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# in a system with the syscall but without support
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# in the kernel.
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if e.errno != errno.ENOSYS:
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raise
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self.skipTest(e)
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else:
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# The number of copied bytes can be less than
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# the number of bytes originally requested.
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self.assertIn(i, range(0, 6));
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with open(TESTFN2, 'rb') as in_file:
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self.assertEqual(in_file.read(), data[:i])
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@unittest.skipUnless(hasattr(os, 'copy_file_range'), 'test needs os.copy_file_range()')
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def test_copy_file_range_offset(self):
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TESTFN4 = support.TESTFN + ".4"
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data = b'0123456789'
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bytes_to_copy = 6
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in_skip = 3
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out_seek = 5
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create_file(support.TESTFN, data)
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self.addCleanup(support.unlink, support.TESTFN)
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in_file = open(support.TESTFN, 'rb')
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self.addCleanup(in_file.close)
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in_fd = in_file.fileno()
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out_file = open(TESTFN4, 'w+b')
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self.addCleanup(support.unlink, TESTFN4)
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self.addCleanup(out_file.close)
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out_fd = out_file.fileno()
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try:
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i = os.copy_file_range(in_fd, out_fd, bytes_to_copy,
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offset_src=in_skip,
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offset_dst=out_seek)
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except OSError as e:
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# Handle the case in which Python was compiled
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# in a system with the syscall but without support
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# in the kernel.
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if e.errno != errno.ENOSYS:
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raise
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self.skipTest(e)
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else:
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# The number of copied bytes can be less than
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# the number of bytes originally requested.
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self.assertIn(i, range(0, bytes_to_copy+1));
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with open(TESTFN4, 'rb') as in_file:
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read = in_file.read()
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# seeked bytes (5) are zero'ed
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self.assertEqual(read[:out_seek], b'\x00'*out_seek)
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# 012 are skipped (in_skip)
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# 345678 are copied in the file (in_skip + bytes_to_copy)
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self.assertEqual(read[out_seek:],
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data[in_skip:in_skip+i])
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# Test attributes on return values from os.*stat* family.
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class StatAttributeTests(unittest.TestCase):

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

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Expose :func:`copy_file_range` as a low level API in the :mod:`os` module.

‎Modules/clinic/posixmodule.c.h‎

Lines changed: 107 additions & 1 deletion
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‎Modules/posixmodule.c‎

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@@ -117,6 +117,10 @@ corresponding Unix manual entries for more information on calls.");
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#include <sched.h>
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#endif
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#ifdef HAVE_COPY_FILE_RANGE
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#include <unistd.h>
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#endif
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#if !defined(CPU_ALLOC) && defined(HAVE_SCHED_SETAFFINITY)
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#undef HAVE_SCHED_SETAFFINITY
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#endif
@@ -9455,8 +9459,74 @@ os_pwritev_impl(PyObject *module, int fd, PyObject *buffers, Py_off_t offset,
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}
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#endif /* HAVE_PWRITEV */
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#ifdef HAVE_COPY_FILE_RANGE
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/*[clinic input]
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os.copy_file_range
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src: int
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Source file descriptor.
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dst: int
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Destination file descriptor.
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count: Py_ssize_t
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Number of bytes to copy.
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offset_src: object = None
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Starting offset in src.
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offset_dst: object = None
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Starting offset in dst.
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Copy count bytes from one file descriptor to another.
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If offset_src is None, then src is read from the current position;
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respectively for offset_dst.
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[clinic start generated code]*/
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static PyObject *
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os_copy_file_range_impl(PyObject *module, int src, int dst, Py_ssize_t count,
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PyObject *offset_src, PyObject *offset_dst)
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/*[clinic end generated code: output=1a91713a1d99fc7a input=42fdce72681b25a9]*/
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{
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off_t offset_src_val, offset_dst_val;
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off_t *p_offset_src = NULL;
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off_t *p_offset_dst = NULL;
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Py_ssize_t ret;
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int async_err = 0;
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/* The flags argument is provided to allow
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* for future extensions and currently must be to 0. */
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int flags = 0;
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if (count < 0) {
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PyErr_SetString(PyExc_ValueError, "negative value for 'count' not allowed");
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return NULL;
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}
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if (offset_src != Py_None) {
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if (!Py_off_t_converter(offset_src, &offset_src_val)) {
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return NULL;
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}
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p_offset_src = &offset_src_val;
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}
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if (offset_dst != Py_None) {
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if (!Py_off_t_converter(offset_dst, &offset_dst_val)) {
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return NULL;
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}
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p_offset_dst = &offset_dst_val;
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}
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do {
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Py_BEGIN_ALLOW_THREADS
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ret = copy_file_range(src, p_offset_src, dst, p_offset_dst, count, flags);
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Py_END_ALLOW_THREADS
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} while (ret < 0 && errno == EINTR && !(async_err = PyErr_CheckSignals()));
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if (ret < 0) {
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return (!async_err) ? posix_error() : NULL;
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}
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return PyLong_FromSsize_t(ret);
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}
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#endif /* HAVE_COPY_FILE_RANGE*/
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#ifdef HAVE_MKFIFO
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/*[clinic input]
@@ -13432,6 +13502,7 @@ static PyMethodDef posix_methods[] = {
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OS_POSIX_SPAWN_METHODDEF
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OS_POSIX_SPAWNP_METHODDEF
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OS_READLINK_METHODDEF
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OS_COPY_FILE_RANGE_METHODDEF
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OS_RENAME_METHODDEF
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OS_REPLACE_METHODDEF
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OS_RMDIR_METHODDEF

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