os_linux: implement virtual memory allocator;

Tuprules.tup

@@ -80,7 +80,7 @@ endif
 ## Linux
 ifeq ($(PLATFORM),linux)
   linux = y
-  CFLAGS += -D_POSIX_C_SOURCE=200809L
+  CFLAGS += -D_POSIX_C_SOURCE=200809L -D_DEFAULT_SOURCE
   CFLAGS += -DLOVR_GL
   LDFLAGS += -lm -lpthread -ldl
   LDFLAGS += -Wl,-rpath,\$ORIGIN

src/core/os.h

@@ -145,6 +145,11 @@ double os_get_time(void);
 void os_sleep(double seconds);
 void os_request_permission(os_permission permission);
 
+void* os_vm_init(size_t size);
+bool os_vm_free(void* p, size_t size);
+bool os_vm_commit(void* p, size_t size);
+bool os_vm_release(void* p, size_t size);
+
 void os_poll_events(void);
 void os_on_quit(fn_quit* callback);
 void os_on_focus(fn_focus* callback);

src/core/os_linux.c

@@ -4,6 +4,7 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include <pwd.h>
+#include <sys/mman.h>
 
 #include "os_glfw.h"
 
@@ -51,6 +52,22 @@ void os_on_permission(fn_permission* callback) {
   //
 }
 
+void* os_vm_init(size_t size) {
+  return mmap(NULL, size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+}
+
+bool os_vm_free(void* p, size_t size) {
+  return !munmap(p, size);
+}
+
+bool os_vm_commit(void* p, size_t size) {
+  return !mprotect(p, size, PROT_READ | PROT_WRITE);
+}
+
+bool os_vm_release(void* p, size_t size) {
+  return !madvise(p, size, MADV_DONTNEED);
+}
+
 size_t os_get_home_directory(char* buffer, size_t size) {
   const char* path = getenv("HOME");