backend-drm: simplify compile time array copy

In drm_fb_get_from_dmabuf() we have some compile time array copies, and
multiple static_assert() calls are needed (for safety). This makes the
code unpleasant to read.

Add ARRAY_COPY macro, to simplify the code.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>

libweston/backend-drm/fb.c

@@ -267,30 +267,9 @@ drm_fb_get_from_dmabuf(struct linux_dmabuf_buffer *dmabuf,
 	fb->refcnt = 1;
 	fb->type = BUFFER_DMABUF;
 
-	static_assert(ARRAY_LENGTH(import_mod.fds) ==
+	ARRAY_COPY(import_mod.fds, dmabuf->attributes.fd);
-		      ARRAY_LENGTH(dmabuf->attributes.fd),
+	ARRAY_COPY(import_mod.strides, dmabuf->attributes.stride);
-		      "GBM and linux_dmabuf FD size must match");
+	ARRAY_COPY(import_mod.offsets, dmabuf->attributes.offset);
-	static_assert(sizeof(import_mod.fds) == sizeof(dmabuf->attributes.fd),
-		      "GBM and linux_dmabuf FD size must match");
-	memcpy(import_mod.fds, dmabuf->attributes.fd, sizeof(import_mod.fds));
-
-	static_assert(ARRAY_LENGTH(import_mod.strides) ==
-		      ARRAY_LENGTH(dmabuf->attributes.stride),
-		      "GBM and linux_dmabuf stride size must match");
-	static_assert(sizeof(import_mod.strides) ==
-		      sizeof(dmabuf->attributes.stride),
-		      "GBM and linux_dmabuf stride size must match");
-	memcpy(import_mod.strides, dmabuf->attributes.stride,
-	       sizeof(import_mod.strides));
-
-	static_assert(ARRAY_LENGTH(import_mod.offsets) ==
-		      ARRAY_LENGTH(dmabuf->attributes.offset),
-		      "GBM and linux_dmabuf offset size must match");
-	static_assert(sizeof(import_mod.offsets) ==
-		      sizeof(dmabuf->attributes.offset),
-		      "GBM and linux_dmabuf offset size must match");
-	memcpy(import_mod.offsets, dmabuf->attributes.offset,
-	       sizeof(import_mod.offsets));
 
 	fb->bo = gbm_bo_import(backend->gbm, GBM_BO_IMPORT_FD_MODIFIER,
 			       &import_mod, GBM_BO_USE_SCANOUT);
@@ -303,18 +282,8 @@ drm_fb_get_from_dmabuf(struct linux_dmabuf_buffer *dmabuf,
 	fb->size = 0;
 	fb->fd = backend->drm.fd;
 
-	static_assert(ARRAY_LENGTH(fb->strides) ==
+	ARRAY_COPY(fb->strides, dmabuf->attributes.stride);
-		      ARRAY_LENGTH(dmabuf->attributes.stride),
+	ARRAY_COPY(fb->offsets, dmabuf->attributes.offset);
-		      "drm_fb and dmabuf stride size must match");
-	static_assert(sizeof(fb->strides) == sizeof(dmabuf->attributes.stride),
-		      "drm_fb and dmabuf stride size must match");
-	memcpy(fb->strides, dmabuf->attributes.stride, sizeof(fb->strides));
-	static_assert(ARRAY_LENGTH(fb->offsets) ==
-		      ARRAY_LENGTH(dmabuf->attributes.offset),
-		      "drm_fb and dmabuf offset size must match");
-	static_assert(sizeof(fb->offsets) == sizeof(dmabuf->attributes.offset),
-		      "drm_fb and dmabuf offset size must match");
-	memcpy(fb->offsets, dmabuf->attributes.offset, sizeof(fb->offsets));
 
 	fb->format = pixel_format_get_info(dmabuf->attributes.format);
 	if (!fb->format) {

shared/helpers.h

@@ -41,6 +41,25 @@ extern "C" {
 #define ARRAY_LENGTH(a) (sizeof (a) / sizeof (a)[0])
 #endif
 
+#define STRING(s) #s
+
+/**
+ * Compile-time copy of hardcoded arrays.
+ *
+ * @param dst the array to copy to.
+ * @param src the source array.
+ */
+#ifndef ARRAY_COPY
+#define ARRAY_COPY(dst, src) \
+do { \
+	static_assert(ARRAY_LENGTH(src) == ARRAY_LENGTH(dst), \
+		      "src and dst sizes must match"); \
+	static_assert(sizeof(src) == sizeof(dst), \
+		      "src and dst sizes must match"); \
+	memcpy((src), (dst), sizeof(src)); \
+} while (0)
+#endif
+
 /**
  * Returns the smaller of two values.
  *