partitioning/writer: Clear first 1MiB of disk for old remnants

During testing gparted still found the old ISO remnants before GPT
within the protective MBR at LBA0, so we now clear that out when
formatting the disk.

Signed-off-by: Ikey Doherty <[email protected]>

Author: ikeycode

crates/partitioning/src/writer.rs

@@ -3,7 +3,7 @@
 //
 // SPDX-License-Identifier: MPL-2.0
 
-use std::{fs, io::Write};
+use std::{fs, io::{Write, Seek}};
 
 use disks::BlockDevice;
 use gpt::{mbr, partition_types, GptConfig};
@@ -100,6 +100,15 @@ impl<'a> DiskWriter<'a> {
     fn apply_changes(&self, device: &mut fs::File, writable: bool) -> Result<(), WriteError> {
         let mut gpt_table = if self.planner.wipe_disk() {
             if writable {
+                // Zero out the first MiB to clear any old partition tables and boot sectors
+                // Write 16*64 KiB = 1 MiB of zeros to the start of the disk
+                let zeros = [0u8; 65_536];
+                device.seek(std::io::SeekFrom::Start(0))?;
+                for _ in 0..16 {
+                    device.write_all(&zeros)?;
+                }
+                device.flush()?;
+
                 let mbr = mbr::ProtectiveMBR::with_lb_size(
                     u32::try_from((self.device.size() / 512) - 1).unwrap_or(0xFF_FF_FF_FF),
                 );