From db830643d21e7c33ec7deb875d45a108290c7100 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Sat, 15 Feb 2020 19:46:00 +0100
Subject: [PATCH] shm: prefer posix_fallocate over ftruncate

---
 shm.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/shm.c b/shm.c
index 3f3ccf21..33095e74 100644
--- a/shm.c
+++ b/shm.c
@@ -6,6 +6,7 @@
 #include <sys/types.h>
 #include <sys/mman.h>
 #include <linux/memfd.h>
+#include <fcntl.h>
 
 #include <pixman.h>
 
@@ -123,9 +124,19 @@ shm_get_buffer(struct wl_shm *shm, int width, int height, unsigned long cookie)
     size = stride * height;
     LOG_DBG("cookie=%lx: allocating new buffer: %zu KB", cookie, size / 1024);
 
-    if (ftruncate(pool_fd, size) == -1) {
-        LOG_ERRNO("failed to truncate SHM pool");
-        goto err;
+    int err = posix_fallocate(pool_fd, 0, size);
+    if (err != 0) {
+        static bool failure_logged = false;
+
+        if (!failure_logged) {
+            failure_logged = true;
+            LOG_ERRNO_P("failed to fallocate", err);
+        }
+
+        if (ftruncate(pool_fd, size) == -1) {
+            LOG_ERRNO("failed to truncate SHM pool");
+            goto err;
+        }
     }
 
     mmapped = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, pool_fd, 0);