From 119017c7033d6a9a692e67805029a88f8e8108ba Mon Sep 17 00:00:00 2001
From: Berkus Decker <berkus+github@metta.systems>
Date: Fri, 20 Nov 2020 03:26:19 +0200
Subject: [PATCH] [wip] Add boot memory regions info

---
 nucleus/src/boot_info.rs | 128 +++++++++++++++++++++++++++++++++++++++
 nucleus/src/main.rs      |   1 +
 2 files changed, 129 insertions(+)
 create mode 100644 nucleus/src/boot_info.rs

diff --git a/nucleus/src/boot_info.rs b/nucleus/src/boot_info.rs
new file mode 100644
index 0000000..7777bc0
--- /dev/null
+++ b/nucleus/src/boot_info.rs
@@ -0,0 +1,128 @@
+#[derive(Default, Copy, Clone)]
+struct BootInfoMemRegion {
+    pub start: PhysAddr,
+    pub end: PhysAddr,
+}
+
+impl BootInfoMemRegion {
+    pub const fn new() -> BootInfoMemRegion {
+        BootInfoMemRegion {
+            start: PhysAddr::zero(),
+            end: PhysAddr::zero(),
+        }
+    }
+
+    pub fn size(&self) -> u64 {
+        self.end - self.start
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.start == self.end
+    }
+}
+
+const NUM_MEM_REGIONS: usize = 16;
+
+pub enum BootInfoError {
+    NoFreeMemRegions,
+}
+
+#[derive(Default)]
+struct BootInfo {
+    pub regions: [BootInfoMemRegion; NUM_MEM_REGIONS],
+    pub max_slot_pos: usize,
+}
+
+impl BootInfo {
+    pub const fn new() -> BootInfo {
+        BootInfo {
+            regions: [BootInfoMemRegion::new(); NUM_MEM_REGIONS],
+            max_slot_pos: 0,
+        }
+    }
+
+    pub fn insert_region(&mut self, reg: BootInfoMemRegion) -> Result<(), BootInfoError> {
+        if reg.is_empty() {
+            return Ok(());
+        }
+        assert!(reg.start <= reg.end);
+        for region in self.regions.iter_mut() {
+            if region.is_empty() {
+                *region = reg;
+                return Ok(());
+            }
+        }
+        return Err(BootInfoError::NoFreeMemRegions);
+    }
+
+    pub fn alloc_region(&mut self, size_bits: usize) -> Result<PhysAddr, BootInfoError> {
+        let mut reg_index: usize = 0;
+        let mut reg: BootInfoMemRegion = BootInfoMemRegion::new();
+        let mut rem_small: BootInfoMemRegion = BootInfoMemRegion::new();
+        let mut rem_large: BootInfoMemRegion = BootInfoMemRegion::new();
+        /*
+         * Search for a free mem region that will be the best fit for an allocation. We favour allocations
+         * that are aligned to either end of the region. If an allocation must split a region we favour
+         * an unbalanced split. In both cases we attempt to use the smallest region possible. In general
+         * this means we aim to make the size of the smallest remaining region smaller (ideally zero)
+         * followed by making the size of the largest remaining region smaller.
+         */
+        for (i, reg_iter) in self.regions.iter().enumerate() {
+            let mut new_reg: BootInfoMemRegion = BootInfoMemRegion::new();
+
+            /* Determine whether placing the region at the start or the end will create a bigger left over region */
+            if reg_iter.start.align_up(1u64 << size_bits) - reg_iter.start
+                < reg_iter.end - reg_iter.end.align_down(1u64 << size_bits)
+            {
+                new_reg.start = reg_iter.start.align_up(1u64 << size_bits);
+                new_reg.end = new_reg.start + (1u64 << size_bits);
+            } else {
+                new_reg.end = reg_iter.end.align_down(1u64 << size_bits);
+                new_reg.start = new_reg.end - (1u64 << size_bits);
+            }
+            if new_reg.end > new_reg.start
+                && new_reg.start >= reg_iter.start
+                && new_reg.end <= reg_iter.end
+            {
+                let mut new_rem_small: BootInfoMemRegion = BootInfoMemRegion::new();
+                let mut new_rem_large: BootInfoMemRegion = BootInfoMemRegion::new();
+
+                if new_reg.start - reg_iter.start < reg_iter.end - new_reg.end {
+                    new_rem_small.start = reg_iter.start;
+                    new_rem_small.end = new_reg.start;
+                    new_rem_large.start = new_reg.end;
+                    new_rem_large.end = reg_iter.end;
+                } else {
+                    new_rem_large.start = reg_iter.start;
+                    new_rem_large.end = new_reg.start;
+                    new_rem_small.start = new_reg.end;
+                    new_rem_small.end = reg_iter.end;
+                }
+                if reg.is_empty()
+                    || (new_rem_small.size() < rem_small.size())
+                    || (new_rem_small.size() == rem_small.size()
+                        && new_rem_large.size() < rem_large.size())
+                {
+                    reg = new_reg;
+                    rem_small = new_rem_small;
+                    rem_large = new_rem_large;
+                    reg_index = i;
+                }
+            }
+        }
+        if reg.is_empty() {
+            panic!("Kernel init failed: not enough memory\n");
+        }
+        /* Remove the region in question */
+        self.regions[reg_index] = BootInfoMemRegion::new();
+        /* Add the remaining regions in largest to smallest order */
+        self.insert_region(rem_large);
+        if self.insert_region(rem_small).is_err() {
+            println!("BootInfo::alloc_region(): wasted {} bytes due to alignment, try to increase NUM_MEM_REGIONS", rem_small.size());
+        }
+        Ok(reg.start)
+    }
+}
+
+#[link_section = ".data.boot"] // @todo put zero-initialized stuff to .bss.boot!
+static BOOT_INFO: sync::NullLock<BootInfo> = sync::NullLock::new(BootInfo::new());
diff --git a/nucleus/src/main.rs b/nucleus/src/main.rs
index 57d396b..7832155 100644
--- a/nucleus/src/main.rs
+++ b/nucleus/src/main.rs
@@ -32,6 +32,7 @@ use architecture_not_supported_sorry;
 #[macro_use]
 pub mod arch;
 pub use arch::*;
+mod boot_info;
 mod devices;
 mod macros;
 mod mm;