disk: use seek to determine file length

Add a new disk-specific DiskGetLen trait which uses io::Seek instead of
File::metadata() to determine the length so that it works on raw block
devices (e.g. /dev/sda) as well as regular files.

BUG=b:146811529
TEST=`crosvm run --disk /dev/sda` and verify block device length

Change-Id: I6936863490efaa479a3c8745c75c373748c800a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1990855
Reviewed-by: Zach Reizner <zachr@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Tested-by: Trent Begin <tbegin@chromium.org>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/sys_util/src/file_traits.rs b/sys_util/src/file_traits.rs
index 7e615d6..c4b1082 100644
--- a/sys_util/src/file_traits.rs
+++ b/sys_util/src/file_traits.rs
@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 use std::fs::File;
-use std::io::{Error, ErrorKind, Result};
+use std::io::{Error, ErrorKind, Result, Seek, SeekFrom};
 use std::os::unix::io::{AsRawFd, RawFd};
 
 use data_model::VolatileSlice;