[PATCH x11spice] Use separate buffer for primary surface to fix graphical corruption

[Brendan Shanks <bshanks@xxxxxxxxxxxxxxx>]

The 'display->fullscreen' SHM segment was previously being used for both
x11spice's internal change scanning and as the spice primary surface.
I don't think spice wants anything else writing to the primary surface,
and this caused sporadic test failures and graphical corruption.

Create a separate SHM segment 'display->primary' and use it only for the
primary surface.

Signed-off-by: Brendan Shanks <bshanks@xxxxxxxxxxxxxxx>
---
 src/display.c | 20 +++++++++++++++++++-
 src/display.h |  1 +
 src/main.c    |  2 +-
 src/session.c |  2 +-
 4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/display.c b/src/display.c
index 01e0e85..77b4d4e 100644
--- a/src/display.c
+++ b/src/display.c
@@ -461,12 +461,25 @@ void destroy_shm_image(display_t *d, shm_image_t *shmi)
 
 int display_create_screen_images(display_t *d)
 {
+    /* 'primary' and 'fullscreen' don't need to be SHM, normal buffers would work
+     * fine. Using SHM for all buffers is simpler though, and has no real downsides.
+     */
+    d->primary = create_shm_image(d, 0, 0);
+    if (!d->primary) {
+        return X11SPICE_ERR_NOSHM;
+    }
+
     d->fullscreen = create_shm_image(d, 0, 0);
-    if (!d->fullscreen)
+    if (!d->fullscreen) {
+        destroy_shm_image(d, d->primary);
+        d->primary = NULL;
         return X11SPICE_ERR_NOSHM;
+    }
 
     d->scanline = create_shm_image(d, 0, 1);
     if (!d->scanline) {
+        destroy_shm_image(d, d->primary);
+        d->primary = NULL;
         destroy_shm_image(d, d->fullscreen);
         d->fullscreen = NULL;
         return X11SPICE_ERR_NOSHM;
@@ -477,6 +490,11 @@ int display_create_screen_images(display_t *d)
 
 void display_destroy_screen_images(display_t *d)
 {
+    if (d->primary) {
+        destroy_shm_image(d, d->primary);
+        d->primary = NULL;
+    }
+
     if (d->fullscreen) {
         destroy_shm_image(d, d->fullscreen);
         d->fullscreen = NULL;
diff --git a/src/display.h b/src/display.h
index dc4254b..27bc829 100644
--- a/src/display.h
+++ b/src/display.h
@@ -55,6 +55,7 @@ typedef struct {
 
     const xcb_query_extension_reply_t *xfixes_ext;
 
+    shm_image_t *primary;
     shm_image_t *fullscreen;
     shm_image_t *scanline;
 
diff --git a/src/main.c b/src/main.c
index cecadc8..71cbb46 100644
--- a/src/main.c
+++ b/src/main.c
@@ -108,7 +108,7 @@ int main(int argc, char *argv[])
     /*------------------------------------------------------------------------
     **  Start up a spice server
     **----------------------------------------------------------------------*/
-    rc = spice_start(&session.spice, &session.options, session.display.fullscreen);
+    rc = spice_start(&session.spice, &session.options, session.display.primary);
     if (rc)
         goto exit;
     spice_started = 1;
diff --git a/src/session.c b/src/session.c
index 1e59415..4d72e14 100644
--- a/src/session.c
+++ b/src/session.c
@@ -352,7 +352,7 @@ int session_recreate_primary(session_t *s)
 
     rc = display_create_screen_images(&s->display);
     if (rc == 0) {
-        shm_image_t *f = s->display.fullscreen;
+        shm_image_t *f = s->display.primary;
         rc = spice_create_primary(&s->spice, f->w, f->h, f->bytes_per_line, f->shmaddr);
     }
 
-- 
2.17.1

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