copy: copy_file_range: handle ENOENT for CIFS

* src/copy.c (sparse_copy): Fallback to standard copy upon ENOENT,
which was seen intermittently across CIFS file systems.
* NEWS: Mention the bug fix, though qualify it as an "issue"
rather than a bug, as coreutils is likely only highlighting
a CIFS bug in this case.
Fixes https://bugs.gnu.org/60455

NEWS

@@ -25,6 +25,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   which may have resulted in data corruption.
   [bug introduced in coreutils-7.5 and enabled by default in coreutils-9.0]
 
+  cp, mv, and install now handle ENOENT failures across CIFS file systems,
+  falling back from copy_file_range to a better supported standard copy.
+  [issue introduced in coreutils-9.0]
+
   'mv --backup=simple f d/' no longer mistakenly backs up d/f to f~.
   [bug introduced in coreutils-9.1]
 

src/copy.c

@@ -290,6 +290,11 @@ sparse_copy (int src_fd, int dest_fd, char **abuf, size_t buf_size,
             if (errno == EPERM && *total_n_read == 0)
               break;
 
+            /* ENOENT was seen sometimes across CIFS shares, resulting in
+               no data being copied, but subsequent standard copies succeed.  */
+            if (errno == ENOENT && *total_n_read == 0)
+              break;
+
             if (errno == EINTR)
               n_copied = 0;
             else