On 23/10/15 20:32, Anna Schumaker wrote:

+    len = stat.st_size;
+
+    fd_out = open(argv[2], O_CREAT|O_WRONLY|O_TRUNC, 0644);
+    if (fd_out == \-1) {
+        perror("open (argv[2])");
+        exit(EXIT_FAILURE);
+    }
+
+    do {
+        ret = copy_file_range(fd_in, NULL, fd_out, NULL, len, 0);
+        if (ret == \-1) {
+            perror("copy_file_range");
+            exit(EXIT_FAILURE);
+        }
+
+        len \-= ret;
+    } while (len > 0);

Is this an infinite loop if len decreases before the copy completes?
Perhaps this should be: while (len && ret);

Otherwise this set looks good.

I'm a bit worried about the sparse expansion and default reflinking
which might preclude cp(1) from using this call in most cases, but I will
test and try to use it. coreutils has heuristics for determining if files
are remote, which we might use to restrict to that use case.

thanks,
Pádraig.