Refactor GPT creation and move it to separate module

Author: phil-opp

src/gpt.rs

@@ -0,0 +1,70 @@
+use anyhow::Context;
+use std::{
+    fs::{self, File},
+    io::{self, Seek},
+    path::Path,
+};
+
+pub fn create_gpt_disk(fat_image: &Path, out_gpt_path: &Path) -> anyhow::Result<()> {
+    // create new file
+    let mut disk = fs::OpenOptions::new()
+        .create(true)
+        .truncate(true)
+        .read(true)
+        .write(true)
+        .open(&out_gpt_path)
+        .with_context(|| format!("failed to create GPT file at `{}`", out_gpt_path.display()))?;
+
+    // set file size
+    let partition_size: u64 = fs::metadata(&fat_image)
+        .context("failed to read metadata of fat image")?
+        .len();
+    let disk_size = partition_size + 1024 * 64; // for GPT headers
+    disk.set_len(disk_size)
+        .context("failed to set GPT image file length")?;
+
+    // create a protective MBR at LBA0 so that disk is not considered
+    // unformatted on BIOS systems
+    let mbr = gpt::mbr::ProtectiveMBR::with_lb_size(
+        u32::try_from((disk_size / 512) - 1).unwrap_or(0xFF_FF_FF_FF),
+    );
+    mbr.overwrite_lba0(&mut disk)
+        .context("failed to write protective MBR")?;
+
+    // create new GPT structure
+    let block_size = gpt::disk::LogicalBlockSize::Lb512;
+    let mut gpt = gpt::GptConfig::new()
+        .writable(true)
+        .initialized(false)
+        .logical_block_size(block_size)
+        .create_from_device(Box::new(&mut disk), None)
+        .context("failed to create GPT structure in file")?;
+    gpt.update_partitions(Default::default())
+        .context("failed to update GPT partitions")?;
+
+    // add new EFI system partition and get its byte offset in the file
+    let partition_id = gpt
+        .add_partition("boot", partition_size, gpt::partition_types::EFI, 0, None)
+        .context("failed to add boot EFI partition")?;
+    let partition = gpt
+        .partitions()
+        .get(&partition_id)
+        .context("failed to open boot partition after creation")?;
+    let start_offset = partition
+        .bytes_start(block_size)
+        .context("failed to get start offset of boot partition")?;
+
+    // close the GPT structure and write out changes
+    gpt.write().context("failed to write out GPT changes")?;
+
+    // place the FAT filesystem in the newly created partition
+    disk.seek(io::SeekFrom::Start(start_offset))
+        .context("failed to seek to start offset")?;
+    io::copy(
+        &mut File::open(&fat_image).context("failed to open FAT image")?,
+        &mut disk,
+    )
+    .context("failed to copy FAT image to GPT disk")?;
+
+    Ok(())
+}

src/lib.rs

@@ -76,6 +76,7 @@ use std::{
 };
 
 mod fat;
+mod gpt;
 
 const KERNEL_FILE_NAME: &str = "kernel-x86_64";
 
@@ -92,54 +93,9 @@ pub fn create_uefi_disk_image(
 
     fat::create_fat_filesystem(files, &out_fat_path)
         .context("failed to create UEFI FAT filesystem")?;
-    create_gpt_disk(out_fat_path, out_gpt_path);
+    gpt::create_gpt_disk(out_fat_path, out_gpt_path)
+        .context("failed to create UEFI GPT disk image")?;
 
     Ok(())
 }
 
-fn create_gpt_disk(fat_image: &Path, out_gpt_path: &Path) {
-    // create new file
-    let mut disk = fs::OpenOptions::new()
-        .create(true)
-        .truncate(true)
-        .read(true)
-        .write(true)
-        .open(&out_gpt_path)
-        .unwrap();
-
-    // set file size
-    let partition_size: u64 = fs::metadata(&fat_image).unwrap().len();
-    let disk_size = partition_size + 1024 * 64; // for GPT headers
-    disk.set_len(disk_size).unwrap();
-
-    // create a protective MBR at LBA0 so that disk is not considered
-    // unformatted on BIOS systems
-    let mbr = gpt::mbr::ProtectiveMBR::with_lb_size(
-        u32::try_from((disk_size / 512) - 1).unwrap_or(0xFF_FF_FF_FF),
-    );
-    mbr.overwrite_lba0(&mut disk).unwrap();
-
-    // create new GPT structure
-    let block_size = gpt::disk::LogicalBlockSize::Lb512;
-    let mut gpt = gpt::GptConfig::new()
-        .writable(true)
-        .initialized(false)
-        .logical_block_size(block_size)
-        .create_from_device(Box::new(&mut disk), None)
-        .unwrap();
-    gpt.update_partitions(Default::default()).unwrap();
-
-    // add new EFI system partition and get its byte offset in the file
-    let partition_id = gpt
-        .add_partition("boot", partition_size, gpt::partition_types::EFI, 0, None)
-        .unwrap();
-    let partition = gpt.partitions().get(&partition_id).unwrap();
-    let start_offset = partition.bytes_start(block_size).unwrap();
-
-    // close the GPT structure and write out changes
-    gpt.write().unwrap();
-
-    // place the FAT filesystem in the newly created partition
-    disk.seek(io::SeekFrom::Start(start_offset)).unwrap();
-    io::copy(&mut File::open(&fat_image).unwrap(), &mut disk).unwrap();
-}