block: Remove redundant BlockBackend trait

BlockBackend predated the disk_file trait family and only carried
logical_size and physical_size, which the disk backends expose
through the disk_file traits DiskSize and PhysicalSize.

It added no polymorphism while its Read, Write and Seek supertraits
forced an unused cursor. Dropping the trait removes the dead code
it was keeping alive.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

block/src/formats/vhdx/internal/mod.rs

@@ -19,7 +19,6 @@ use self::bat::{BatEntry, VhdxBatError};
 use self::header::{RegionInfo, RegionTableEntry, VhdxHeader, VhdxHeaderError};
 use self::io::VhdxIoError;
 use self::metadata::{DiskSpec, VhdxMetadataError};
-use crate::BlockBackend;
 use crate::aligned_file::AlignedFile;
 
 mod bat;
@@ -207,12 +206,8 @@ impl Seek for Vhdx {
     }
 }
 
-impl BlockBackend for Vhdx {
-    fn logical_size(&self) -> result::Result<u64, crate::Error> {
-        Ok(self.virtual_disk_size())
-    }
-
-    fn physical_size(&self) -> result::Result<u64, crate::Error> {
+impl Vhdx {
+    pub(crate) fn physical_size(&self) -> result::Result<u64, crate::Error> {
         self.aligned
             .file()
             .metadata()

block/src/formats/vhdx/mod.rs

@@ -22,7 +22,7 @@ pub use internal::{Vhdx, VhdxError};
 use self::worker::sync::VhdxSync;
 use crate::async_io::{AsyncIo, BorrowedDiskFd, DiskFileError};
 use crate::error::{BlockError, BlockErrorKind, BlockResult, ErrorOp};
-use crate::{BlockBackend, Error, disk_file};
+use crate::{Error, disk_file};
 
 #[derive(Debug)]
 pub struct VhdxDisk {