Add sync syscall

src/Enclave.edl

@@ -15,5 +15,6 @@ enclave {
         void ocall_print_string([in, string] const char* msg);
         int ocall_run_new_task(void);
         void ocall_gettimeofday([out] long* seconds, [out] long* microseconds);
+        void ocall_sync(void);
     };
 };

src/libos/include/syscall.h

@@ -19,6 +19,8 @@ extern ssize_t occlum_write(int fd, const void* buf, size_t size);
 extern ssize_t occlum_writev(int fd, const struct iovec* iov, int count);
 extern off_t occlum_lseek(int fd, off_t offset, int whence);
 
+extern int occlum_sync(void);
+
 extern int occlum_pipe(int fds[2]);
 extern int occlum_pipe2(int fds[2], int flags);
 

src/libos/src/fs/mod.rs

@@ -153,3 +153,12 @@ pub fn do_dup3(old_fd: FileDesc, new_fd: FileDesc, flags: u32) -> Result<FileDes
     file_table.put_at(new_fd, file, close_on_spawn);
     Ok(new_fd)
 }
+
+pub fn do_sync() -> Result<(), Error> {
+    unsafe { ocall_sync(); }
+    Ok(())
+}
+
+extern {
+    fn ocall_sync() -> sgx_status_t;
+}

src/libos/src/syscall/mod.rs

@@ -540,6 +540,19 @@ pub extern "C" fn occlum_dup3(old_fd: c_int, new_fd: c_int, flags: c_int)
     }
 }
 
+#[no_mangle]
+pub extern "C" fn occlum_sync() -> c_int
+{
+    match fs::do_sync() {
+        Ok(()) => {
+            0 as c_int
+        }
+        Err(e) => {
+            e.errno.as_retval()
+        }
+    }
+}
+
 // TODO: handle tz: timezone_t
 #[no_mangle]
 pub extern "C" fn occlum_gettimeofday(tv: *mut timeval_t) -> c_int

src/libos/src/syscall/syscall_entry.c

@@ -85,6 +85,10 @@ long dispatch_syscall(int num, long arg0, long arg1, long arg2, long arg3, long
         ret = occlum_getppid();
         break;
     }
+    case SYS_sync: {
+        ret = occlum_sync();
+        break;
+    }
     case SYS_mmap: {
         DECL_SYSCALL_ARG(void*, addr, arg0);
         DECL_SYSCALL_ARG(size_t, length, arg1);

src/pal/pal.c

@@ -205,6 +205,10 @@ void ocall_gettimeofday(long* seconds, long* microseconds) {
     *microseconds = tv.tv_usec;
 }
 
+void ocall_sync(void) {
+    sync();
+}
+
 
 /* Application entry */
 int SGX_CDECL main(int argc, const char *argv[])