Add qcow_utils for exposing qcow functions as a C library

This C library will be use by the VM launcher to create the qcow2 files
used for persistent VM data.

CQ-DEPEND=CL:884263
BUG=none
TEST=cargo test --all -- --test-threads=1

Change-Id: Ibd7f71d2e3f1f72f781978f014865d2161f033f5
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/875116

Cargo.lock

@@ -1,15 +1,3 @@
-[root]
-name = "x86_64"
-version = "0.1.0"
-dependencies = [
- "byteorder 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "data_model 0.1.0",
- "kvm 0.1.0",
- "kvm_sys 0.1.0",
- "libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
- "sys_util 0.1.0",
-]
-
 [[package]]
 name = "bitflags"
 version = "1.0.1"
@@ -38,6 +26,7 @@ dependencies = [
  "libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugin_proto 0.5.0",
  "qcow 0.1.0",
+ "qcow_utils 0.1.0",
  "sys_util 0.1.0",
  "vm_control 0.1.0",
  "x86_64 0.1.0",
@@ -184,6 +173,14 @@ dependencies = [
  "sys_util 0.1.0",
 ]
 
+[[package]]
+name = "qcow_utils"
+version = "0.1.0"
+dependencies = [
+ "libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
+ "qcow 0.1.0",
+]
+
 [[package]]
 name = "rand"
 version = "0.3.20"
@@ -243,6 +240,18 @@ dependencies = [
  "sys_util 0.1.0",
 ]
 
+[[package]]
+name = "x86_64"
+version = "0.1.0"
+dependencies = [
+ "byteorder 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "data_model 0.1.0",
+ "kvm 0.1.0",
+ "kvm_sys 0.1.0",
+ "libc 0.2.34 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sys_util 0.1.0",
+]
+
 [metadata]
 "checksum bitflags 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "b3c30d3802dfb7281680d6285f2ccdaa8c2d8fee41f93805dba5c4cf50dc23cf"
 "checksum byteorder 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ff81738b726f5d099632ceaffe7fb65b90212e8dce59d518729e7e8634032d3d"

Cargo.toml

@@ -24,6 +24,7 @@ vm_control = { path = "vm_control" }
 data_model = { path = "data_model" }
 qcow = { path = "qcow" }
 plugin_proto = { path = "plugin_proto", optional = true }
+qcow_utils = { path = "qcow_utils" }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 x86_64 = { path = "x86_64" }

qcow_utils/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "qcow_utils"
+version = "0.1.0"
+authors = ["The Chromium OS Authors"]
+
+[lib]
+path = "src/qcow_utils.rs"
+crate-type = ["cdylib"]
+
+[dependencies]
+libc = "*"
+qcow = { path = "../qcow" }

qcow_utils/src/qcow_utils.h

@@ -0,0 +1,10 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdint.h>
+
+// Exported interface to basic qcow functionality to be used from C.
+
+// Create a basic, empty qcow2 file that can grow to `virtual_size` at `path`.
+int create_qcow_with_size(const char *path, uint64_t virtual_size);

qcow_utils/src/qcow_utils.rs

@@ -0,0 +1,47 @@
+// Copyright 2018 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Exported interface to basic qcow functionality to be used from C.
+
+extern crate libc;
+extern crate qcow;
+
+use std::ffi::CStr;
+use std::fs::OpenOptions;
+use std::os::raw::{c_char, c_int};
+use libc::EINVAL;
+
+use qcow::QcowHeader;
+
+#[no_mangle]
+pub extern "C" fn create_qcow_with_size(path: *const c_char,
+                                        virtual_size: u64) -> c_int {
+    let c_str = unsafe {
+        // NULL pointers are checked, but this will access any other invalid pointer passed from C
+        // code. It's the caller's responsibility to pass a valid pointer.
+        if path.is_null() {
+            return -EINVAL;
+        }
+        CStr::from_ptr(path)
+    };
+    let file_path = match c_str.to_str() {
+        Ok(s) => s,
+        Err(_) => return -EINVAL,
+    };
+
+    let h = QcowHeader::create_for_size(virtual_size);
+    let mut file = match OpenOptions::new()
+                            .create(true)
+                            .read(true)
+                            .write(true)
+                            .open(file_path) {
+        Ok(f) => f,
+        Err(_) => return -1,
+    };
+
+    match h.write_to(&mut file) {
+        Ok(()) => 0,
+        Err(_) => -1,
+    }
+}