Kernel: Implement basic shared memory objects

These can allocate memory that can be shared between processes using
a global key. There is currenly no safety checks meaning anyone can
map any shared memory object just by trying to map every possible key.

libc/include/sys/banan-os.h

@@ -36,6 +36,11 @@ int poweroff(int command);
 
 int load_keymap(const char* path);
 
+// Create shared memory object and return its key or -1 on error
+long smo_create(size_t size, int prot);
+// Map shared memory object defined by its key and return address or null on error
+void* smo_map(long key);
+
 __END_DECLS
 
 #endif

libc/include/sys/syscall.h

@@ -74,6 +74,8 @@ __BEGIN_DECLS
 	O(SYS_LISTEN,			listen)			\
 	O(SYS_PSELECT,			pselect)		\
 	O(SYS_TRUNCATE,			truncate)		\
+	O(SYS_SMO_CREATE,		smo_create)		\
+	O(SYS_SMO_MAP,			smo_map)		\
 
 enum Syscall
 {

libc/sys/banan-os.cpp

@@ -16,3 +16,16 @@ int load_keymap(const char* path)
 {
 	return syscall(SYS_LOAD_KEYMAP, path);
 }
+
+long smo_create(size_t size, int prot)
+{
+	return syscall(SYS_SMO_CREATE, size, prot);
+}
+
+void* smo_map(long key)
+{
+	long ret = syscall(SYS_SMO_MAP, key);
+	if (ret < 0)
+		return nullptr;
+	return reinterpret_cast<void*>(ret);
+}