Report errors if loopback device creation fails

src/anbox/cmds/container_manager.cpp

@@ -100,9 +100,17 @@ bool anbox::cmds::ContainerManager::setup_mounts() {
   if (!fs::exists(android_rootfs_dir))
     fs::create_directory(android_rootfs_dir);
 
-  auto loop_device = common::LoopDeviceAllocator::new_device();
-  if (!loop_device)
+  std::shared_ptr<common::LoopDevice> loop_device;
+
+  try {
+    loop_device = common::LoopDeviceAllocator::new_device();
+  } catch (const std::exception& e) {
+    ERROR("Could not create loopback device: %s", e.what());
+    return false;
+  } catch (...) {
+    ERROR("Could not create loopback device");
     return false;
+  }
 
   if (!loop_device->attach_file(android_img_path)) {
     ERROR("Failed to attach Android rootfs image to loopback device");

src/anbox/common/loop_device.cpp

@@ -18,7 +18,10 @@
 #include "anbox/common/loop_device.h"
 #include "anbox/defer_action.h"
 
+#include <system_error>
+
 #include <linux/loop.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>
 
@@ -27,7 +30,7 @@ namespace common {
 std::shared_ptr<LoopDevice> LoopDevice::create(const boost::filesystem::path &path) {
   const auto fd = ::open(path.c_str(), O_RDWR);
   if (fd < 0)
-    return nullptr;
+    throw std::system_error{errno, std::system_category()};
 
   return std::shared_ptr<LoopDevice>(new LoopDevice(Fd{fd}, path));
 }

src/anbox/common/loop_device_allocator.cpp

@@ -23,9 +23,12 @@
 #include <boost/filesystem.hpp>
 
 #include <linux/loop.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>
 
+#include <system_error>
+
 namespace fs = boost::filesystem;
 
 namespace {
@@ -38,19 +41,15 @@ namespace common {
 std::shared_ptr<LoopDevice> LoopDeviceAllocator::new_device() {
   const auto ctl_fd = ::open(loop_control_path, O_RDWR);
   if (ctl_fd < 0)
-    return nullptr;
+    throw std::system_error{errno, std::system_category()};
 
   DeferAction close_ctl_fd{[&]() { ::close(ctl_fd); }};
 
   const auto device_nr = ::ioctl(ctl_fd, LOOP_CTL_GET_FREE);
   if (device_nr < 0)
-    return nullptr;
-
-  const auto path = utils::string_format("%s%d", base_loop_path, device_nr);
-  if (!fs::exists(path))
-    return nullptr;
+    throw std::system_error{errno, std::system_category()};
 
-  return LoopDevice::create(path);
+  return LoopDevice::create(utils::string_format("%s%d", base_loop_path, device_nr));
 }
 } // namespace common
 } // namespace anbox