Port recent rename changes to RHEL 7 + NFS

Problem reported by Ted Zlatanov in:
http://lists.gnu.org/archive/html/emacs-devel/2017-08/msg00082.html
* src/fileio.c (Frename_file): On RHEL 7 + NFS, renameat2 can fail
with errno == EINVAL when it is not supported.  So treat that case
like errno == ENOSYS.  Also, when ok_if_already_exists is neither
nil nor an integer, just call plain rename; this avoids an extra
syscall to renameat2 when the latter fails with errno == EINVAL or
ENOSYS or ENOENT.

1 files changed, 30 insertions, 15 deletions

diff --git a/src/fileio.c b/src/fileio.c
index 0264c9fa1d8..db760d9b22d 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -2344,23 +2344,38 @@ This is what happens in interactive use with M-x.  */)
   encoded_file = ENCODE_FILE (file);
   encoded_newname = ENCODE_FILE (newname);
 
-  if (renameat_noreplace (AT_FDCWD, SSDATA (encoded_file),
-                          AT_FDCWD, SSDATA (encoded_newname))
-      == 0)
-    return Qnil;
-  int rename_errno = errno;
+  /* If the filesystem is case-insensitive and the file names are
+     identical but for the case, don't worry whether the destination
+     already exists: the caller simply wants to change the letter-case
+     of the file name.  */
+  bool plain_rename
+    = ((!NILP (ok_if_already_exists) && !INTEGERP (ok_if_already_exists))
+       || (file_name_case_insensitive_p (SSDATA (encoded_file))
+           && ! NILP (Fstring_equal (Fdowncase (file), Fdowncase (newname)))));
+
+  int rename_errno;
+  if (!plain_rename)
+    {
+      if (renameat_noreplace (AT_FDCWD, SSDATA (encoded_file),
+                              AT_FDCWD, SSDATA (encoded_newname))
+          == 0)
+        return Qnil;
+
+      rename_errno = errno;
+      switch (rename_errno)
+        {
+        case EEXIST: case EINVAL: case ENOSYS:
+          barf_or_query_if_file_exists (newname, rename_errno == EEXIST,
+                                        "rename to it",
+                                        INTEGERP (ok_if_already_exists),
+                                        false);
+          plain_rename = true;
+          break;
+        }
+    }
 
-  if (rename_errno == EEXIST || rename_errno == ENOSYS)
+  if (plain_rename)
     {
-      /* If the filesystem is case-insensitive and the file names are
-         identical but for the case, don't ask for confirmation: they
-         simply want to change the letter-case of the file name.  */
-      if ((NILP (ok_if_already_exists) || INTEGERP (ok_if_already_exists))
-          && (! file_name_case_insensitive_p (SSDATA (encoded_file))
-              || NILP (Fstring_equal (Fdowncase (file), Fdowncase (newname)))))
-        barf_or_query_if_file_exists (newname, rename_errno == EEXIST,
-                                      "rename to it",
-                                      INTEGERP (ok_if_already_exists), false);
       if (rename (SSDATA (encoded_file), SSDATA (encoded_newname)) == 0)
         return Qnil;
       rename_errno = errno;