1 files changed, 29 insertions, 8 deletions

diff --git a/src/platform/wayland/drag.c b/src/platform/wayland/drag.c
index 07e31b5..4317d0d 100644
--- a/src/platform/wayland/drag.c
+++ b/src/platform/wayland/drag.c
@@ -136,15 +136,16 @@ static const struct wl_data_source_listener source_listener = {
     .action = source_action,
 };
 
+/* A seat whose press is still held over the origin window; its serial starts the drag. */
 static struct seat *drag_seat(struct wayland_display *c, struct wayland_surface *origin)
 {
     struct wayland_surface *root = surface_root(origin);
     struct seat *active = c->active_seat ? c->active_seat : c->seats;
-    if (active && active->press_serial &&
+    if (active && seat_held_press_serial(active) &&
         surface_root(active->press_surface) == root)
         return active;
     for (struct seat *s = c->seats; s; s = s->next)
-        if (s->press_serial && surface_root(s->press_surface) == root)
+        if (seat_held_press_serial(s) && surface_root(s->press_surface) == root)
             return s;
     return NULL;
 }
@@ -153,20 +154,33 @@ bool wayland_display_drag_start(struct wayland_display *c, struct wayland_surfac
                              const struct yasl_private_drag_image *image,
                              const struct yasl_private_drag_listener *l, void *ud)
 {
-    if (!c || !origin || origin->conn != c || !l || c->drag.source)
+    if (!c || !origin || origin->conn != c || !l) {
+        errno = EINVAL;
         return false;
+    }
+    if (c->drag.source) {
+        errno = EBUSY;
+        return false;
+    }
     struct seat *seat = drag_seat(c, origin);
-    if (!seat)
+    if (!seat) {
+        errno = ESTALE;
         return false;
+    }
     struct wl_data_device *device = clipboard_data_device(seat->clipboard);
-    if (!device || wl_data_device_get_version(device) < 3)
+    if (!device || wl_data_device_get_version(device) < 3) {
+        errno = ENOTSUP;
         return false;
+    }
     c->drag.scale_120 = origin->scale_120;
-    if (image && !icon_create(c, image))
+    if (image && !icon_create(c, image)) {
+        errno = ENOMEM;
         return false;
+    }
     struct wl_data_source *s = wl_data_device_manager_create_data_source(c->data_manager);
     if (!s) {
         icon_clear(&c->drag.icon);
+        errno = ENOMEM;
         return false;
     }
     c->drag.source = s;
@@ -180,7 +194,7 @@ bool wayland_display_drag_start(struct wayland_display *c, struct wayland_surfac
         c->drag.toplevel = xdg_toplevel_drag_manager_v1_get_xdg_toplevel_drag(
                 c->toplevel_drag_mgr, s);
     wl_data_device_start_drag(device, s, seat->press_surface->surface,
-                              c->drag.icon.surface, seat->press_serial);
+                              c->drag.icon.surface, seat_held_press_serial(seat));
     if (image)
         icon_show(c, image);
     wl_display_flush(c->wl);
@@ -196,8 +210,14 @@ void wayland_display_drag_cancel(struct wayland_display *c)
 bool wayland_surface_drag_carry(struct wayland_surface *w, struct yasl_private_vector2i offset)
 {
     struct wayland_display *c = w ? w->conn : NULL;
-    if (!c || !c->drag.source || !c->drag.toplevel || !w->toplevel)
+    if (!c || !c->drag.source || !w->toplevel) {
+        errno = EINVAL;
+        return false;
+    }
+    if (!c->drag.toplevel) {
+        errno = ENOTSUP;
         return false;
+    }
     uint32_t scale = c->drag.scale_120;
     xdg_toplevel_drag_v1_attach(c->drag.toplevel, w->toplevel,
                                 yasl_private_scale_to_logical(offset.x, scale),
@@ -210,6 +230,7 @@ bool wayland_surface_place_under_pointer(struct wayland_surface *w, struct yasl_
 {
     (void)w;
     (void)at;
+    errno = ENOTSUP;
     return false;
 }