Reenable sendfile fast-copy syscall on Solaris

Doc/library/shutil.rst

@@ -452,7 +452,7 @@ the use of userspace buffers in Python as in "``outfd.write(infd.read())``".
 
 On macOS `fcopyfile`_ is used to copy the file content (not metadata).
 
-On Linux :func:`os.sendfile` is used.
+On Linux and Solaris :func:`os.sendfile` is used.
 
 On Windows :func:`shutil.copyfile` uses a bigger default buffer size (1 MiB
 instead of 64 KiB) and a :func:`memoryview`-based variant of
@@ -464,6 +464,9 @@ file then shutil will silently fallback on using less efficient
 
 .. versionchanged:: 3.8
 
+.. versionchanged:: 3.10
+    Solaris now uses :func:`os.sendfile` rather than no fast-copy operation.
+
 .. _shutil-copytree-example:
 
 copytree example

Lib/shutil.py

@@ -50,7 +50,7 @@ elif _WINDOWS:
     import nt
 
 COPY_BUFSIZE = 1024 * 1024 if _WINDOWS else 64 * 1024
-_USE_CP_SENDFILE = hasattr(os, "sendfile") and sys.platform.startswith("linux")
+_USE_CP_SENDFILE = hasattr(os, "sendfile") and sys.platform.startswith(("linux", "sunos"))
 _HAS_FCOPYFILE = posix and hasattr(posix, "_fcopyfile")  # macOS
 
 # CMD defaults in Windows 10
@@ -114,7 +114,7 @@ def _fastcopy_fcopyfile(fsrc, fdst, flags):
 def _fastcopy_sendfile(fsrc, fdst):
     """Copy data from one regular mmap-like fd to another by using
     high-performance sendfile(2) syscall.
-    This should work on Linux >= 2.6.33 only.
+    This should work on Linux >= 2.6.33 and Solaris only.
     """
     # Note: copyfileobj() is left alone in order to not introduce any
     # unexpected breakage. Possible risks by using zero-copy calls
@@ -269,7 +269,7 @@ def copyfile(src, dst, *, follow_symlinks=True):
                     return dst
                 except _GiveupOnFastCopy:
                     pass
-            # Linux
+            # Linux / Solaris
             elif _USE_CP_SENDFILE:
                 try:
                     _fastcopy_sendfile(fsrc, fdst)