towbootctl: Rework calculation of image size

The image size is now a multiple of 512 bytes
and there is slightly less empty space.

Author: YtvwlD

towbootctl/src/image.rs

@@ -26,10 +26,14 @@ impl Image {
             .create(true)
             .truncate(true)
             .open(path)?);
+        // make sure the image size is a multiple of 512
+        // gdisk warns otherwise and OVMF seems to ignore the disk in some cases
+        // also, keep a spare megabyte for the partition table and alignment
+        let size = size.next_multiple_of(512) + 1024 * 1024;
         file.set_len(size)?;
         // protective MBR
         let mbr = ProtectiveMBR::with_lb_size(
-            u32::try_from((size / 512) - 1).unwrap_or(0xFF_FF_FF_FF)
+            u32::try_from((size / 512) - 1)?
         );
         mbr.overwrite_lba0(&mut file)?;
         let mut disk = GptConfig::new()
@@ -38,7 +42,10 @@ impl Image {
             .create_from_device(file, None)?;
         disk.update_partitions(BTreeMap::new())?;
         debug!("creating partition");
-        disk.add_partition("towboot", size - 1024 * 1024, partition_types::EFI, 0, None)?;
+        // the partition needs to be slightly smaller than the disk image
+        disk.add_partition(
+            "towboot", size - 64 * 1024, partition_types::EFI, 0, None,
+        )?;
         let partitions = disk.partitions().clone();
         let (_, partition) = partitions.iter().next().unwrap();
         let file = disk.write()?;

towbootctl/src/lib.rs

@@ -21,9 +21,6 @@ mod image;
 use bochs::bochsrc;
 use image::Image;
 
-/// How big the image should be
-pub const DEFAULT_IMAGE_SIZE: u64 = 50*1024*1024;
-
 /// Where to place the 32-bit EFI file
 pub const IA32_BOOT_PATH: &str = "EFI/Boot/bootia32.efi";
 
@@ -98,15 +95,19 @@ pub fn create_image(
         paths.push((PathBuf::from(src), PathBuf::from(X64_BOOT_PATH)));
     }
 
-    let mut image_size = 0x00_20_00_00;
+    let mut image_size = 0;
     for pair in paths.iter() {
         let file = OpenOptions::new()
             .read(true)
             .open(PathBuf::from(&pair.0))?;
         image_size += file.metadata()?.len();
     }
 
-    info!("creating image at {} (size: {} MiB)", target.display(), image_size / 1024 / 1024);
+    info!(
+        "creating image at {} (size: {} MiB)",
+        target.display(),
+        image_size.div_ceil(1024).div_ceil(1024),
+    );
     let mut image = Image::new(target, image_size)?;
     for pair in paths {
         image.add_file(pair.0.as_path(), pair.1.as_path())?