gh-85264: Expose DEV_BSIZE from posixmodule.c

https://pubs.opengroup.org/onlinepubs/009695399/basedefs/sys/stat.h.html

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

Doc/library/os.rst

@@ -2663,6 +2663,16 @@ features:
    .. versionadded:: 3.15
 
 
+.. data:: DEV_BSIZE
+
+   The size, in bytes, of a block as reported by the :attr:`~os.stat_result.st_blocks`
+   field of :class:`~os.stat_result`.  This is typically 512 bytes.
+
+   :ref:`Availability <availability>`: Unix.
+
+   .. versionadded:: 3.15
+
+
 .. function:: pathconf(path, name)
 
    Return system configuration information relevant to a named file. *name*

Modules/posixmodule.c

@@ -18393,6 +18393,17 @@ all_ins(PyObject *m)
     /* STATX_ATTR_* constants are in the stat module */
 #endif /* HAVE_STATX */
 
+    /* Block size for the st_blocks field of stat(2).
+     * st_blocks is in 512-byte units on most platforms. DEV_BSIZE (or BSIZE
+     * as a fallback) from sys/param.h gives the actual platform value. */
+#if defined(HAVE_STRUCT_STAT_ST_BLOCKS)
+#  if defined(DEV_BSIZE)
+    if (PyModule_AddIntConstant(m, "DEV_BSIZE", DEV_BSIZE)) return -1;
+#  elif defined(BSIZE)
+    if (PyModule_AddIntConstant(m, "DEV_BSIZE", BSIZE)) return -1;
+#  endif
+#endif
+
 #if defined(__APPLE__)
     if (PyModule_AddIntConstant(m, "_COPYFILE_DATA", COPYFILE_DATA)) return -1;
     if (PyModule_AddIntConstant(m, "_COPYFILE_STAT", COPYFILE_STAT)) return -1;