partitioning: Add a new Strategy system

While the builtin strategies are arguably quite simple it does offer
quite enough reusable scaffolding that one can implement sane automatic
options for installers and provisioning.

The main focus is on disk wipes, and partition reuse. Such that if we
encounter an existing install we can amend to make it correct, or even
by manual planning APIs offer to delete a large rootfs and split into the
correct layout (xbootldr, anyone?)

In time we'll also support resizing operations but we'll need to get these
bits hooked up for GPT and partition types yet.

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

crates/partitioning/src/lib.rs

@@ -9,3 +9,4 @@ pub mod sparsefile;
 pub use gpt;
 
 pub mod planner;
+pub mod strategy;

crates/partitioning/src/planner.rs

@@ -27,6 +27,8 @@ pub enum PlanError {
     RegionOverlap { start: u64, end: u64 },
     #[error("Region {start}..{end} exceeds disk bounds")]
     RegionOutOfBounds { start: u64, end: u64 },
+    #[error("No free regions available")]
+    NoFreeRegions,
 }
 
 /// A planned modification to the disk's partition layout
@@ -66,8 +68,11 @@ pub struct Planner {
 /// ```
 #[derive(Debug, Clone)]
 pub struct Region {
-    start: u64,
-    end: u64,
+    /// The absolute start position of this region in bytes
+    pub start: u64,
+
+    /// The absolute end position of this region in bytes
+    pub end: u64,
 }
 
 /// Default alignment for partition boundaries (1MiB)
@@ -353,6 +358,13 @@ impl Planner {
     pub fn original_disk(&self) -> &Disk {
         &self.disk
     }
+    /// Plan to initialize a clean partition layout
+    pub fn plan_initialize_disk(&mut self) -> Result<(), PlanError> {
+        debug!("Planning to create new GPT partition table");
+        self.changes.clear(); // Clear any existing changes
+        self.original_regions.clear(); // Clear original partitions
+        Ok(())
+    }
 }
 #[cfg(test)]
 mod tests {