cp(1) bogus error messages on short writes

[piotr]

To reproduce:

$ (ulimit -f 1 && cp /etc/rc /tmp/rc)
cp: /tmp/rc: No such file or directory
$ (ulimit -f 1 && cp /etc/rc /tmp/rc)
cp: /tmp/rc: Undefined error: 0
$

Patch:

diff -rup /usr/src/bin/cp/utils.c cp/utils.c
--- /usr/src/bin/cp/utils.c     Sun Nov 28 20:28:41 2021
+++ cp/utils.c  Fri May  6 23:25:01 2022
@@ -149,8 +149,13 @@ copy_file(FTSENT *entp, int exists)
                                wcount = lseek(to_fd, rcount, SEEK_CUR) == -1 ? 
-1 : rcount;
                        else
                                wcount = write(to_fd, buf, rcount);
-                       if (rcount != wcount || wcount == -1) {
+                       if (wcount == -1) {
                                warn("%s", to.p_path);
+                               rval = 1;
+                               break;
+                       }
+                       if (rcount != wcount) {
+                               warnx("%s: short write", to.p_path);
                                rval = 1;
                                break;
                        }