loader: Condition crates import and usage by feature

We only need SeekFrom, Cursor, struct_util and mem when either
ELF or bzImage are selected.
We only need read_struct_slice for ELF.

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Author: bjzhjing

src/loader/mod.rs

@@ -19,7 +19,10 @@ extern crate vm_memory;
 use std::error::{self, Error as KernelLoaderError};
 use std::ffi::CStr;
 use std::fmt::{self, Display};
-use std::io::{Read, Seek, SeekFrom};
+#[cfg(any(feature = "elf", feature = "bzimage"))]
+use std::io::SeekFrom;
+use std::io::{Read, Seek};
+#[cfg(feature = "elf")]
 use std::mem;
 
 use vm_memory::{Address, Bytes, GuestAddress, GuestMemory, GuestUsize};
@@ -36,6 +39,7 @@ pub mod bootparam;
 #[allow(non_upper_case_globals)]
 #[cfg_attr(feature = "cargo-clippy", allow(clippy::all))]
 mod elf;
+#[cfg(any(feature = "elf", feature = "bzimage"))]
 mod struct_util;
 
 #[derive(Debug, PartialEq)]
@@ -371,6 +375,7 @@ pub fn load_cmdline<M: GuestMemory>(
 #[cfg(test)]
 mod test {
     use super::*;
+    #[cfg(any(feature = "elf", feature = "bzimage"))]
     use std::io::Cursor;
     use vm_memory::{Address, GuestAddress, GuestMemoryMmap};
 

src/loader/struct_util.rs

@@ -40,6 +40,7 @@ pub unsafe fn read_struct<T: Copy, F: Read>(f: &mut F, out: &mut T) -> Result<()
 ///
 /// * `f` - The input to read from.  Often this is a file.
 /// * `len` - The number of structs to fill with data read from `f`.
+#[cfg(feature = "elf")]
 pub unsafe fn read_struct_slice<T: Copy, F: Read>(f: &mut F, len: usize) -> Result<Vec<T>> {
     let mut out: Vec<T> = Vec::with_capacity(len);
     out.set_len(len);
@@ -114,6 +115,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg(feature = "elf")]
     fn struct_slice_read() {
         let orig = vec![
             TestRead {