initial boot partition

2 files changed, 86 insertions, 2 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 73dd870..667e394 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,4 +6,6 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0.66"
 clap = { version = "4.0.29", features = ["derive"] }
+nix = { version = "0.26.1", features = ["ioctl"] }
diff --git a/src/main.rs b/src/main.rs
index 6992905..7052363 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,8 @@
+use anyhow::bail;
 use clap::Parser;
+use std::fs::File;
+use std::io::Write;
+use std::os::unix::io::AsRawFd;
 
 #[derive(Debug, Parser)]
 #[command(author = "The Rustkrazy Authors", version = "v0.1.0", about = "Generate a rustkrazy image.", long_about = None)]
@@ -8,8 +12,86 @@ struct Args {
     overwrite: String,
 }
 
-fn main() {
+#[cfg(target_os = "linux")]
+fn device_size(file: &std::fs::File, path: String) -> anyhow::Result<u64> {
+    use nix::ioctl_read;
+
+    const BLKGETSIZE64_CODE: u8 = 0x12;
+    const BLKGETSIZE64_SEQ: u8 = 114;
+    ioctl_read!(ioctl_blkgetsize64, BLKGETSIZE64_CODE, BLKGETSIZE64_SEQ, u64);
+
+    let fd = file.as_raw_fd();
+
+    let mut dev_size = 0;
+    let dev_size_ptr = &mut dev_size as *mut u64;
+
+    unsafe {
+        match ioctl_blkgetsize64(fd, dev_size_ptr) {
+            Ok(_) => {}
+            Err(_) => bail!("{} does not seem to be a device", path),
+        }
+    }
+
+    Ok(dev_size)
+}
+
+fn write_mbr_partition_table(file: &mut std::fs::File, dev_size: u64) -> anyhow::Result<()> {
+    const NOPART: &[u8] = &[0; 16];
+    const BOOTABLE: &[u8] = &[0x80];
+    const INVALID_CHS: &[u8] = &[0xFF, 0xFF, 0xFE]; // Causes sector values to be used
+    const FAT: &[u8] = &[0xc];
+    const SIGNATURE: &[u8] = &[0x55, 0xAA];
+
+    #[allow(non_upper_case_globals)]
+    const KiB: u32 = 1024;
+    #[allow(non_upper_case_globals)]
+    const MiB: u32 = 1024 * KiB;
+
+    file.write_all(&[0; 446])?; // Boot code
+
+    // Partition 1
+    file.write_all(BOOTABLE)?;
+    file.write_all(INVALID_CHS)?;
+    file.write_all(FAT)?;
+    file.write_all(INVALID_CHS)?;
+    file.write_all(&2048_u32.to_le_bytes())?; // Start at sector 2048
+    file.write_all(&(256 * MiB / 512).to_le_bytes())?; // 256 MiB in size
+
+    // Partition 2 (unused)
+    file.write_all(NOPART)?;
+
+    // Partition 3 (unused)
+    file.write_all(NOPART)?;
+
+    // Partition 4 (unused)
+    file.write_all(NOPART)?;
+
+    file.write_all(SIGNATURE)?;
+
+    Ok(())
+}
+
+fn partition(file: &mut std::fs::File, dev_size: u64) -> anyhow::Result<()> {
+    write_mbr_partition_table(file, dev_size)?;
+
+    Ok(())
+}
+
+fn partition_device(overwrite: String) -> anyhow::Result<()> {
+    let mut file = File::create(overwrite.clone())?;
+
+    let dev_size = device_size(&file, overwrite)?;
+    println!("Destination holds {} bytes", dev_size);
+
+    partition(&mut file, dev_size)?;
+
+    Ok(())
+}
+
+fn main() -> anyhow::Result<()> {
     let args = Args::parse();
 
-    println!("overwriting {}", args.overwrite);
+    partition_device(args.overwrite)?;
+
+    Ok(())
 }