portability: abstract memfd_create away

src/common.hpp

@@ -42,6 +42,7 @@ extern zwlr_layer_shell_v1* wlrLayerShell;
 void spawn(Monitor&, const Arg& arg);
 void setCloexec(int fd);
 [[noreturn]] void die(const char* why);
+[[noreturn]] void diesys(const char* why);
 
 // wayland smart pointers
 template<typename T>

src/main.cpp

@@ -62,7 +62,6 @@ static void onGlobalRemove(void*, wl_registry* registry, uint32_t name);
 static void requireGlobal(const void* p, const char* name);
 static void waylandFlush();
 static void cleanup();
-[[noreturn]] static void diesys(const char* why);
 
 wl_display* display;
 wl_compositor* compositor;

src/shm_buffer.cpp

@@ -1,11 +1,14 @@
 // somebar - dwl bar
 // See LICENSE file for copyright and license details.
 
+#include <fcntl.h>
 #include <sys/mman.h>
+#include <sys/stat.h>
 #include <unistd.h>
 #include "shm_buffer.hpp"
 #include "common.hpp"
 
+static int createAnonShm();
 constexpr int n = 2;
 
 ShmBuffer::ShmBuffer(int w, int h, wl_shm_format format)
@@ -15,8 +18,13 @@ ShmBuffer::ShmBuffer(int w, int h, wl_shm_format format)
 {
 	auto oneSize = stride*size_t(h);
 	auto totalSize = oneSize * n;
-	auto fd = memfd_create("wl_shm", MFD_CLOEXEC);
-	ftruncate(fd, totalSize);
+	auto fd = createAnonShm();
+	if (fd < 0) {
+		diesys("memfd_create");
+	}
+	if (ftruncate(fd, totalSize) < 0) {
+		diesys("ftruncate");
+	}
 	auto pool = wl_shm_create_pool(shm, fd, totalSize);
 	auto ptr = reinterpret_cast<uint8_t*>(mmap(nullptr, totalSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0));
 	_mapping = MemoryMapping {ptr, totalSize};
@@ -34,3 +42,30 @@ ShmBuffer::ShmBuffer(int w, int h, wl_shm_format format)
 uint8_t* ShmBuffer::data() { return _buffers[_current].data; }
 wl_buffer* ShmBuffer::buffer() { return _buffers[_current].buffer.get(); }
 void ShmBuffer::flip() { _current = 1-_current; }
+
+#if defined(__linux__)
+static int createAnonShm() {
+	return memfd_create("wl_shm", MFD_CLOEXEC);
+}
+#elif defined(__FreeBSD__)
+static int createAnonShm() {
+	auto fd = shm_open(SHM_ANON, O_CREAT | O_RDWR, 0600);
+	setCloexec(fd);
+	return fd;
+}
+#elif defined(__OpenBSD__)
+static int createAnonShm() {
+	char name[] = "/wl_shm-XXXXXX";
+	auto fd = shm_mkstemp(name);
+	if (fd >= 0) {
+		auto res = shm_unlink(name);
+		if (res < 0) {
+			return res;
+		}
+	}
+	setCloexec(fd);
+	return fd;
+}
+#else
+#error "your system has no sane method of creating an anonymous shared memory object. no, calling shm_open in a loop is not sane."
+#endif