serve s3: document multipart copy doesn't work #7454

This puts in a workaround for the tests also

cmd/serve/s3/s3_test.go

@@ -113,7 +113,7 @@ func RunS3UnitTests(t *testing.T, name string, start servetest.StartFn) {
 	if *fstest.Verbose {
 		args = append(args, "-verbose")
 	}
-	remoteName := name + "test:"
+	remoteName := "serve" + name + ":"
 	args = append(args, "-remote", remoteName)
 	args = append(args, "-run", "^TestIntegration$")
 	args = append(args, "-list-retries", fmt.Sprint(*fstest.ListRetries))

cmd/serve/s3/serve_s3.md

@@ -55,8 +55,19 @@ Note that setting `disable_multipart_uploads = true` is to work around
 ### Bugs
 
 When uploading multipart files `serve s3` holds all the parts in
-memory. This is a limitaton of the library rclone uses for serving S3
-and will hopefully be fixed at some point.
+memory (see [#7453](https://github.com/rclone/rclone/issues/7453)).
+This is a limitaton of the library rclone uses for serving S3 and will
+hopefully be fixed at some point.
+
+Multipart server side copies do not work (see
+[#7454](https://github.com/rclone/rclone/issues/7454)). These take a
+very long time and eventually fail. The default threshold for
+multipart server side copies is 5G which is the maximum it can be, so
+files above this side will fail to be server side copied.
+
+For a current list of `serve s3` bugs see the [serve
+s3](https://github.com/rclone/rclone/labels/serve%20s3) bug category
+on GitHub.
 
 ### Limitations
 

fstest/fstests/fstests.go

@@ -2146,6 +2146,10 @@ func Run(t *testing.T, opt *Opt) {
 				t.Skip("skipping as ChunkedUpload.Skip is set")
 			}
 
+			if strings.HasPrefix(f.Name(), "serves3") {
+				t.Skip("FIXME skip test - see #7454")
+			}
+
 			do, _ := f.(SetCopyCutoffer)
 			if do == nil {
 				t.Skipf("%T does not implement SetCopyCutoff", f)