Fix the size of a virtio device, backed by a block device

When a virtio device is backed by a block device, the actual size of
the block device file doesn't represent the size as a virtio device.

Fixes #1316

Author: kzys

vmm/src/block_device.rs

@@ -0,0 +1,36 @@
+// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+use std::fs::File;
+use std::io::Error;
+use std::os::raw;
+use sys_util::ioctl_with_mut_ref;
+
+const FS: raw::c_uint = 0x12;
+ioctl_ior_nr!(BLKGETSIZE64, FS, 114, ::std::os::raw::c_ulong);
+
+pub fn get_size(path: &std::path::Path) -> std::result::Result<u64, std::io::Error> {
+    let mut size: u64 = 0;
+
+    let file = File::open(path)?;
+    let ret = unsafe {
+        ioctl_with_mut_ref(&file, BLKGETSIZE64(), &mut size)
+    };
+
+    if ret < 0 {
+        return Err(Error::last_os_error());
+    } else {
+        return Ok(size)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::Path;
+
+    #[test]
+    fn test_invalid_file() {
+        assert!(get_size(&Path::new("/dev/null")).is_err());
+    }
+}

vmm/src/lib.rs

@@ -31,6 +31,7 @@ extern crate memory_model;
 extern crate net_util;
 extern crate rate_limiter;
 extern crate seccomp;
+#[macro_use]
 extern crate sys_util;
 
 /// Syscalls allowed through the seccomp filter.
@@ -41,11 +42,13 @@ pub mod error;
 pub mod signal_handler;
 /// Wrappers over structures used to configure the VMM.
 pub mod vmm_config;
+mod block_device;
 mod vstate;
 
 use std::collections::HashMap;
 use std::fs::{metadata, File, OpenOptions};
 use std::io;
+use std::os::unix::fs::FileTypeExt;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::path::PathBuf;
 use std::process;
@@ -1524,7 +1527,12 @@ impl Vmm {
             if drive_config.drive_id == *drive_id {
                 let metadata = metadata(&drive_config.path_on_host)
                     .map_err(|_| DriveError::BlockDeviceUpdateFailed)?;
-                let new_size = metadata.len();
+                let new_size = if metadata.file_type().is_block_device() {
+                    block_device::get_size(&drive_config.path_on_host)
+                        .map_err(|_| DriveError::BlockDeviceUpdateFailed)?
+                } else {
+                    metadata.len()
+                };
                 if new_size % virtio::block::SECTOR_SIZE != 0 {
                     warn!(
                         "Disk size {} is not a multiple of sector size {}; \