[mutter] kms: Fix meta_kms_crtc_read_state gamma table memory leak

[Jonas Ådahl <jadahl src gnome org>]

commit 73db35c53c71759b3ea4e864db64d1fb57094a1c
Author: Hans de Goede <hdegoede redhat com>
Date:   Mon Aug 5 12:09:29 2019 +0200

    kms: Fix meta_kms_crtc_read_state gamma table memory leak
    
    Before this commit meta_kms_crtc_read_state was overwriting the
    entire MetaKmsCrtcState struct stored in crtc->current_state including
    the gamma (sub)struct.
    
    This effectively zero-s the gamma struct each time before calling
    read_gamma_state, setting the pointers where the previous gamma values
    were stored to NULL without freeing the memory. Luckily this zero-ing
    also sets gamma.size to 0, causing read_gamma_state to re-alloc the
    arrays on each meta_kms_crtc_update_state call. But this does mean that
    were leaking the old gamma arrays on each meta_kms_crtc_update_state call.
    
    This commit fixes this by making meta_kms_crtc_read_state only overwrite
    the other values in the MetaKmsCrtcState struct and leaving the gamma
    sub-struct alone, this will make read_gamma_state correctly re-use the
    gamma tables if the gamma table size is unchanged; or re-alloc them
    (freeing the old ones) if the size has changed, fixing the memory leak.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/713

 src/backends/native/meta-kms-crtc.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)
---
diff --git a/src/backends/native/meta-kms-crtc.c b/src/backends/native/meta-kms-crtc.c
index 2dd2b8da4..b07a6e7d5 100644
--- a/src/backends/native/meta-kms-crtc.c
+++ b/src/backends/native/meta-kms-crtc.c
@@ -110,17 +110,16 @@ meta_kms_crtc_read_state (MetaKmsCrtc       *crtc,
                           MetaKmsImplDevice *impl_device,
                           drmModeCrtc       *drm_crtc)
 {
-  crtc->current_state = (MetaKmsCrtcState) {
-    .rect = {
-      .x = drm_crtc->x,
-      .y = drm_crtc->y,
-      .width = drm_crtc->width,
-      .height = drm_crtc->height,
-    },
-    .is_drm_mode_valid = drm_crtc->mode_valid,
-    .drm_mode = drm_crtc->mode,
+  crtc->current_state.rect = (MetaRectangle) {
+    .x = drm_crtc->x,
+    .y = drm_crtc->y,
+    .width = drm_crtc->width,
+    .height = drm_crtc->height,
   };
 
+  crtc->current_state.is_drm_mode_valid = drm_crtc->mode_valid;
+  crtc->current_state.drm_mode = drm_crtc->mode;
+
   read_gamma_state (crtc, impl_device, drm_crtc);
 }