kernel: DUP_RDONLY and DUP_WRONLY

I probably should've tested DUP_WRONLY too, now that I think about it. TODO?

1 files changed, 28 insertions, 0 deletions

diff --git a/src/kernel/handleset.c b/src/kernel/handleset.c
index a25f5c7..fc2d426 100644
--- a/src/kernel/handleset.c
+++ b/src/kernel/handleset.c
@@ -89,6 +89,34 @@ hs_dup(HandleSet *hs, hid_t from, hid_t to, int flags)
 	fromh = hs_get(hs, from);
 
 	if (*toh) handle_close(*toh);
+
+	if (flags & (DUP_RDONLY | DUP_WRONLY)) {
+		if (!fromh || fromh->type != HANDLE_FILE) {
+			/* only errors out after closing the old handle */
+			*toh = NULL;
+			return -ENOSYS;
+		}
+
+		/* figure out if we need a need handle */
+		bool different = false;
+		different = different || ((flags & DUP_RDONLY) && fromh->writeable);
+		different = different || ((flags & DUP_WRONLY) && fromh->readable);
+
+		if (different) {
+			Handle *new = handle_init(HANDLE_FILE);
+			new->backend = fromh->backend;
+			if (new->backend) new->backend->usehcnt++;
+			new->file_id = fromh->file_id;
+			new->readable  = fromh->readable  && !(flags & DUP_WRONLY);
+			new->writeable = fromh->writeable && !(flags & DUP_RDONLY);
+			new->base = fromh;
+			fromh->refcount++;
+
+			*toh = new;
+			return to;
+		}
+	}
+
 	*toh = fromh;
 	if (fromh) fromh->refcount++;