gh-99726: Add 'fast' argument to os.[l]stat for faster calculation

Doc/library/os.path.rst

@@ -437,6 +437,9 @@ the :mod:`glob` module.)
    :func:`os.lstat`, or :func:`os.stat`.  This function implements the
    underlying comparison used by :func:`samefile` and :func:`sameopenfile`.
 
+   Do not use stat results created with the *fast* argument, as they may be
+   missing information necessary to compare the two files.
+
    .. availability:: Unix, Windows.
 
    .. versionchanged:: 3.4

Doc/library/os.rst

@@ -1037,17 +1037,27 @@ as internal buffering of data.
    .. availability:: Unix.
 
 
-.. function:: fstat(fd)
+.. function:: fstat(fd, *, fast=False)
 
    Get the status of the file descriptor *fd*. Return a :class:`stat_result`
    object.
 
-   As of Python 3.3, this is equivalent to ``os.stat(fd)``.
+   As of Python 3.3, this is equivalent to ``os.stat(fd, fast=fast)``.
+
+   Passing *fast* as ``True`` may omit some information on some platforms
+   for the sake of performance. These omissions are not guaranteed (that is,
+   the information may be returned anyway), and may change between Python
+   releases without a deprecation period or due to operating system updates
+   without warning. See :class:`stat_result` documentation for the fields
+   that are guaranteed to be present under this option.
 
    .. seealso::
 
       The :func:`.stat` function.
 
+   .. versionchanged:: 3.12
+      Added the *fast* parameter.
+
 
 .. function:: fstatvfs(fd, /)
 
@@ -2175,7 +2185,7 @@ features:
       Accepts a :term:`path-like object`.
 
 
-.. function:: lstat(path, *, dir_fd=None)
+.. function:: lstat(path, *, dir_fd=None, fast=False)
 
    Perform the equivalent of an :c:func:`lstat` system call on the given path.
    Similar to :func:`~os.stat`, but does not follow symbolic links. Return a
@@ -2184,8 +2194,15 @@ features:
    On platforms that do not support symbolic links, this is an alias for
    :func:`~os.stat`.
 
+   Passing *fast* as ``True`` may omit some information on some platforms
+   for the sake of performance. These omissions are not guaranteed (that is,
+   the information may be returned anyway), and may change between Python
+   releases without a deprecation period or due to operating system updates
+   without warning. See :class:`stat_result` documentation for the fields
+   that are guaranteed to be present under this option.
+
    As of Python 3.3, this is equivalent to ``os.stat(path, dir_fd=dir_fd,
-   follow_symlinks=False)``.
+   follow_symlinks=False, fast=fast)``.
 
    This function can also support :ref:`paths relative to directory descriptors
    <dir_fd>`.
@@ -2209,6 +2226,9 @@ features:
       Other kinds of reparse points are resolved by the operating system as
       for :func:`~os.stat`.
 
+   .. versionchanged:: 3.12
+      Added the *fast* parameter.
+
 
 .. function:: mkdir(path, mode=0o777, *, dir_fd=None)
 
@@ -2781,7 +2801,7 @@ features:
       for :class:`bytes` paths on Windows.
 
 
-.. function:: stat(path, *, dir_fd=None, follow_symlinks=True)
+.. function:: stat(path, *, dir_fd=None, follow_symlinks=True, fast=False)
 
    Get the status of a file or a file descriptor. Perform the equivalent of a
    :c:func:`stat` system call on the given path. *path* may be specified as
@@ -2806,6 +2826,13 @@ features:
    possible and call :func:`lstat` on the result. This does not apply to
    dangling symlinks or junction points, which will raise the usual exceptions.
 
+   Passing *fast* as ``True`` may omit some information on some platforms
+   for the sake of performance. These omissions are not guaranteed (that is,
+   the information may be returned anyway), and may change between Python
+   releases without a deprecation period or due to operating system updates
+   without warning. See :class:`stat_result` documentation for the fields
+   that are guaranteed to be present under this option.
+
    .. index:: module: stat
 
    Example::
@@ -2838,19 +2865,32 @@ features:
       returns the information for the original path as if
       ``follow_symlinks=False`` had been specified instead of raising an error.
 
+   .. versionchanged:: 3.12
+      Added the *fast* parameter.
+
 
 .. class:: stat_result
 
    Object whose attributes correspond roughly to the members of the
    :c:type:`stat` structure. It is used for the result of :func:`os.stat`,
    :func:`os.fstat` and :func:`os.lstat`.
 
+   When the *fast* argument to these functions is passed ``True``, some
+   information may be reduced or omitted. Those attributes that are
+   guaranteed to be valid, and those currently known to be omitted, are
+   marked in the documentation below. If not specified and you depend on
+   that field, explicitly pass *fast* as ``False`` to ensure it is
+   calculated.
+
    Attributes:
 
    .. attribute:: st_mode
 
       File mode: file type and file mode bits (permissions).
 
+      When *fast* is ``True``, only the file type bits are guaranteed
+      to be valid (the mode bits may be zero).
+
    .. attribute:: st_ino
 
       Platform dependent, but if non-zero, uniquely identifies the
@@ -2865,6 +2905,8 @@ features:
 
       Identifier of the device on which this file resides.
 
+      On Windows, when *fast* is ``True``, this may be zero.
+
    .. attribute:: st_nlink
 
       Number of hard links.
@@ -2883,6 +2925,8 @@ features:
       The size of a symbolic link is the length of the pathname it contains,
       without a terminating null byte.
 
+      This field is guaranteed to be filled when specifying *fast*.
+
    Timestamps:
 
    .. attribute:: st_atime
@@ -2893,6 +2937,8 @@ features:
 
       Time of most recent content modification expressed in seconds.
 
+      This field is guaranteed to be filled when specifying *fast*.
+
    .. attribute:: st_ctime
 
       Platform dependent:
@@ -2909,6 +2955,9 @@ features:
       Time of most recent content modification expressed in nanoseconds as an
       integer.
 
+      This field is guaranteed to be filled when specifying *fast*, subject
+      to the note below.
+
    .. attribute:: st_ctime_ns
 
       Platform dependent:
@@ -2998,12 +3047,16 @@ features:
       :c:func:`GetFileInformationByHandle`. See the ``FILE_ATTRIBUTE_*``
       constants in the :mod:`stat` module.
 
+      This field is guaranteed to be filled when specifying *fast*.
+
    .. attribute:: st_reparse_tag
 
       When :attr:`st_file_attributes` has the ``FILE_ATTRIBUTE_REPARSE_POINT``
       set, this field contains the tag identifying the type of reparse point.
       See the ``IO_REPARSE_TAG_*`` constants in the :mod:`stat` module.
 
+      This field is guaranteed to be filled when specifying *fast*.
+
    The standard module :mod:`stat` defines functions and constants that are
    useful for extracting information from a :c:type:`stat` structure. (On
    Windows, some items are filled with dummy values.)
@@ -3039,6 +3092,10 @@ features:
       files as :const:`S_IFCHR`, :const:`S_IFIFO` or :const:`S_IFBLK`
       as appropriate.
 
+   .. versionchanged:: 3.12
+      Added the *fast* argument and defined the minimum set of returned
+      fields.
+
 .. function:: statvfs(path)
 
    Perform a :c:func:`statvfs` system call on the given path.  The return value is

Include/internal/pycore_fileutils_windows.h

@@ -0,0 +1,77 @@
+#ifndef Py_INTERNAL_FILEUTILS_WINDOWS_H
+#define Py_INTERNAL_FILEUTILS_WINDOWS_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "Py_BUILD_CORE must be defined to include this header"
+#endif
+
+#ifdef MS_WINDOWS
+
+#if !defined(NTDDI_WIN10_NI) || !(NTDDI_VERSION >= NTDDI_WIN10_NI)
+typedef struct _FILE_STAT_BASIC_INFORMATION {
+    LARGE_INTEGER FileId;
+    LARGE_INTEGER CreationTime;
+    LARGE_INTEGER LastAccessTime;
+    LARGE_INTEGER LastWriteTime;
+    LARGE_INTEGER ChangeTime;
+    LARGE_INTEGER AllocationSize;
+    LARGE_INTEGER EndOfFile;
+    ULONG FileAttributes;
+    ULONG ReparseTag;
+    ULONG NumberOfLinks;
+    ULONG DeviceType;
+    ULONG DeviceCharacteristics;
+} FILE_STAT_BASIC_INFORMATION;
+
+typedef enum _FILE_INFO_BY_NAME_CLASS {
+    FileStatByNameInfo,
+    FileStatLxByNameInfo,
+    FileCaseSensitiveByNameInfo,
+    FileStatBasicByNameInfo,
+    MaximumFileInfoByNameClass
+} FILE_INFO_BY_NAME_CLASS;
+#endif
+
+typedef BOOL (WINAPI *PGetFileInformationByName)(
+    PCWSTR FileName,
+    FILE_INFO_BY_NAME_CLASS FileInformationClass,
+    PVOID FileInfoBuffer,
+    ULONG FileInfoBufferSize
+);
+
+static inline BOOL GetFileInformationByName(
+    PCWSTR FileName,
+    FILE_INFO_BY_NAME_CLASS FileInformationClass,
+    PVOID FileInfoBuffer,
+    ULONG FileInfoBufferSize
+) {
+    static PGetFileInformationByName GetFileInformationByName = NULL;
+    static int GetFileInformationByName_init = -1;
+
+    if (GetFileInformationByName_init < 0) {
+        HMODULE hMod = LoadLibraryW(L"api-ms-win-core-file-l2-1-4");
+        GetFileInformationByName_init = 0;
+        if (hMod) {
+            GetFileInformationByName = (PGetFileInformationByName)GetProcAddress(
+                hMod, "GetFileInformationByName");
+            if (GetFileInformationByName) {
+                GetFileInformationByName_init = 1;
+            } else {
+                FreeLibrary(hMod);
+            }
+        }
+    }
+
+    if (GetFileInformationByName_init <= 0) {
+        SetLastError(ERROR_NOT_SUPPORTED);
+        return FALSE;
+    }
+    return GetFileInformationByName(FileName, FileInformationClass, FileInfoBuffer, FileInfoBufferSize);
+}
+
+#endif
+
+#endif

Include/internal/pycore_global_strings.h

@@ -389,6 +389,7 @@ struct _Py_global_strings {
         STRUCT_FOR_ID(false)
         STRUCT_FOR_ID(family)
         STRUCT_FOR_ID(fanout)
+        STRUCT_FOR_ID(fast)
         STRUCT_FOR_ID(fd)
         STRUCT_FOR_ID(fd2)
         STRUCT_FOR_ID(fdel)

Lib/asyncio/proactor_events.py

@@ -734,7 +734,7 @@ async def _sock_sendfile_native(self, sock, file, offset, count):
         except (AttributeError, io.UnsupportedOperation) as err:
             raise exceptions.SendfileNotAvailableError("not a regular file")
         try:
-            fsize = os.fstat(fileno).st_size
+            fsize = os.fstat(fileno, fast=True).st_size
         except OSError:
             raise exceptions.SendfileNotAvailableError("not a regular file")
         blocksize = count if count else fsize

Lib/asyncio/unix_events.py

@@ -307,7 +307,7 @@ async def create_unix_server(
             # Check for abstract socket. `str` and `bytes` paths are supported.
             if path[0] not in (0, '\x00'):
                 try:
-                    if stat.S_ISSOCK(os.stat(path).st_mode):
+                    if stat.S_ISSOCK(os.stat(path, fast=True).st_mode):
                         os.remove(path)
                 except FileNotFoundError:
                     pass
@@ -363,7 +363,7 @@ async def _sock_sendfile_native(self, sock, file, offset, count):
         except (AttributeError, io.UnsupportedOperation) as err:
             raise exceptions.SendfileNotAvailableError("not a regular file")
         try:
-            fsize = os.fstat(fileno).st_size
+            fsize = os.fstat(fileno, fast=True).st_size
         except OSError:
             raise exceptions.SendfileNotAvailableError("not a regular file")
         blocksize = count if count else fsize
@@ -472,7 +472,7 @@ def __init__(self, loop, pipe, protocol, waiter=None, extra=None):
         self._closing = False
         self._paused = False
 
-        mode = os.fstat(self._fileno).st_mode
+        mode = os.fstat(self._fileno, fast=True).st_mode
         if not (stat.S_ISFIFO(mode) or
                 stat.S_ISSOCK(mode) or
                 stat.S_ISCHR(mode)):
@@ -607,7 +607,7 @@ def __init__(self, loop, pipe, protocol, waiter=None, extra=None):
         self._conn_lost = 0
         self._closing = False  # Set when close() or write_eof() called.
 
-        mode = os.fstat(self._fileno).st_mode
+        mode = os.fstat(self._fileno, fast=True).st_mode
         is_char = stat.S_ISCHR(mode)
         is_fifo = stat.S_ISFIFO(mode)
         is_socket = stat.S_ISSOCK(mode)

Lib/compileall.py

@@ -220,7 +220,7 @@ def compile_file(fullname, ddir=None, force=False, rx=None, quiet=0,
         if tail == '.py':
             if not force:
                 try:
-                    mtime = int(os.stat(fullname).st_mtime)
+                    mtime = int(os.stat(fullname, fast=True).st_mtime)
                     expect = struct.pack('<4sLL', importlib.util.MAGIC_NUMBER,
                                          0, mtime & 0xFFFF_FFFF)
                     for cfile in opt_cfiles.values():

Lib/filecmp.py

@@ -50,8 +50,8 @@ def cmp(f1, f2, shallow=True):
 
     """
 
-    s1 = _sig(os.stat(f1))
-    s2 = _sig(os.stat(f2))
+    s1 = _sig(os.stat(f1, fast=True))
+    s2 = _sig(os.stat(f2, fast=True))
     if s1[0] != stat.S_IFREG or s2[0] != stat.S_IFREG:
         return False
     if shallow and s1 == s2:
@@ -159,12 +159,12 @@ def phase2(self): # Distinguish files, directories, funnies
 
             ok = True
             try:
-                a_stat = os.stat(a_path)
+                a_stat = os.stat(a_path, fast=True)
             except OSError:
                 # print('Can\'t stat', a_path, ':', why.args[1])
                 ok = False
             try:
-                b_stat = os.stat(b_path)
+                b_stat = os.stat(b_path, fast=True)
             except OSError:
                 # print('Can\'t stat', b_path, ':', why.args[1])
                 ok = False