move memory discovery to the Architecture trait

Memory discovery (finding how much we have, where etc...) shouldn't be
hardcoded in `mm/mod.rs`. Instead it should be in the Architecture trait
so that each platform can do its thing (riscv/arm => device tree, x86 =>
multiboot info or e820).

Originaly I just wanted a `memory_regions -> impl Iterator<Item=T>`
method in the Architecture trait. But oh boy no...
Currently a method that returns an impl Trait is not possible (rustc
1.59.0-nightly).
In the future, this should be possible, see: rust-lang/rust#63066

Meanwhile, this is what I came up with.
Since I can't return an impl Trait but I can pass one as parameter, I
have a `for_all_memory_regions` method that creates the iterator and
then calls the closure with that parameter. Code that uses that is a bit
more ugly and less clear than if I could have returned an impl Trait,
but it should do for now. This MUST be fixed when the above issue is
resolved.
Also the type signatures are a bit *complex*, this is due to my vicious
fight with the rust borrow-checking-and-mighty-type-checking gods of
Rust.

Last but not least, a quote from the great:
Tout est simple, tout est complexe, a vous de trouver la solution, une solution peut en cacher une autre
-- Garnier

src/arch/mod.rs

@@ -1,8 +1,10 @@
+
 #[cfg(target_arch = "arm")]
 mod arm32;
 #[cfg(target_arch = "riscv64")]
 mod riscv64;
 
+
 use cfg_if::cfg_if;
 
 use crate::mm;
@@ -12,10 +14,10 @@ pub type MemoryImpl = riscv64::sv39::PageTable;
 #[cfg(target_arch = "riscv64")]
 pub type InterruptsImpl = riscv64::interrupts::Interrupts;
 
-pub fn new_arch() -> impl Architecture {
+pub fn new_arch(info: usize) -> impl Architecture {
     cfg_if! {
         if #[cfg(target_arch = "riscv64")] {
-            riscv64::Riscv64::new()
+            riscv64::Riscv64::new(info)
         } else if #[cfg(target_arch = "arm")] {
             arm32::Arm32::new()
         } else {
@@ -26,6 +28,11 @@ pub fn new_arch() -> impl Architecture {
 
 pub trait Architecture {
     unsafe extern "C" fn _start() -> !;
+
+    fn new(info: usize) -> Self;
+
+    fn for_all_memory_regions<F: FnMut(&mut dyn Iterator<Item=(usize, usize)>)>(&self, f: F);
+    fn for_all_reserved_memory_regions<F: FnMut(&mut dyn Iterator<Item=(usize, usize)>)>(&self, f: F);
 }
 
 pub trait ArchitectureMemory {

src/arch/riscv64/mod.rs

@@ -7,12 +7,9 @@ pub mod interrupts;
 pub mod registers;
 pub mod sv39;
 
-pub struct Riscv64 {}
 
-impl Riscv64 {
-    pub fn new() -> Self {
-        Self {}
-    }
+pub struct Riscv64 {
+    device_tree: fdt::Fdt<'static>,
 }
 
 impl Architecture for Riscv64 {
@@ -21,4 +18,32 @@ impl Architecture for Riscv64 {
     unsafe extern "C" fn _start() -> ! {
         asm!("la sp, STACK_START", "call k_main", options(noreturn));
     }
+
+    fn new(info: usize) -> Self {
+        let device_tree = unsafe { fdt::Fdt::from_ptr(info as *const u8).unwrap() };
+
+        Self { device_tree }
+    }
+
+    fn for_all_memory_regions<F: FnMut(&mut dyn Iterator<Item=(usize, usize)>)>(&self, mut f: F) {
+        let memory = self.device_tree.memory();
+        let mut regions = memory
+            .regions()
+            .map(|region| {
+                (region.starting_address as usize, region.size.unwrap_or(0))
+            });
+
+        f(&mut regions);
+    }
+
+    fn for_all_reserved_memory_regions<F: FnMut(&mut dyn Iterator<Item=(usize, usize)>)>(&self, mut f: F) {
+        let reserved_memory = self.device_tree.find_node("/reserved-memory").unwrap();
+
+        let mut regions = reserved_memory
+            .children()
+            .flat_map(|child| child.reg().unwrap())
+            .map(|region| (region.starting_address as usize, region.size.unwrap_or(0)));
+
+        f(&mut regions);
+    }
 }

src/main.rs

@@ -4,6 +4,8 @@
 #![feature(fn_align)]
 #![feature(naked_functions)]
 #![feature(custom_test_frameworks)]
+#![feature(associated_type_defaults)]
+#![feature(type_alias_impl_trait)]
 #![test_runner(crate::kernel_tests::runner)]
 #![reexport_test_harness_main = "ktests_launch"]
 
@@ -28,7 +30,7 @@ extern "C" fn k_main(_core_id: usize, device_tree_ptr: usize) -> ! {
     #[cfg(test)]
     ktests_launch();
 
-    let _arch = arch::new_arch();
+    let mut arch = arch::new_arch(device_tree_ptr);
 
     kprintln!("GoOSe is booting");
 
@@ -43,9 +45,7 @@ extern "C" fn k_main(_core_id: usize, device_tree_ptr: usize) -> ! {
     }
     plic.set_threshold(0);
 
-    let device_tree = unsafe { fdt::Fdt::from_ptr(device_tree_ptr as *const u8).unwrap() };
-
-    let mut memory = mm::MemoryManager::<arch::MemoryImpl>::new(&device_tree);
+    let mut memory = mm::MemoryManager::<arch::MemoryImpl>::new(&arch);
     memory.map_address_space();
 
     kprintln!("[OK] Setup virtual memory");

src/mm/mod.rs

@@ -32,17 +32,18 @@ pub fn is_kernel_page(base: usize) -> bool {
     base >= kernel_start && base < kernel_end
 }
 
-// TODO: shall this be moved to arch/riscv (in the MemoryImpl) ?
-pub fn is_reserved_page(base: usize, device_tree: &fdt::Fdt) -> bool {
-    let reserved_memory = device_tree.find_node("/reserved-memory").unwrap();
-    let mut reserved_pages = reserved_memory
-        .children()
-        .flat_map(|child| child.reg().unwrap())
-        .map(|region| (region.starting_address as usize, region.size.unwrap_or(0)));
-
-    reserved_pages.any(|(region_start, region_size)| {
-        base >= region_start && base <= (region_start + region_size)
-    })
+pub fn is_reserved_page(base: usize, arch: &impl arch::Architecture) -> bool {
+    let mut is_res = false;
+
+    arch.for_all_reserved_memory_regions(|regions| {
+        is_res = regions
+            .map(|(start, size)| (start, size)) // this is a weird hack to fix a type error.
+            .any(|(region_start, region_size)| {
+            base >= region_start && base <= (region_start + region_size)
+        })
+    });
+
+    return is_res;
 }
 
 pub struct MemoryManager<'alloc, T: arch::ArchitectureMemory> {
@@ -51,12 +52,12 @@ pub struct MemoryManager<'alloc, T: arch::ArchitectureMemory> {
 }
 
 impl<'alloc, T: arch::ArchitectureMemory> MemoryManager<'alloc, T> {
-    pub fn new(device_tree: &fdt::Fdt) -> Self {
+    pub fn new(arch: &impl arch::Architecture) -> Self {
         let mut page_manager =
-            page_manager::PageManager::from_device_tree(&device_tree, T::get_page_size());
-        let arch = T::new(&mut page_manager);
+            page_manager::PageManager::from_arch_info(arch, T::get_page_size());
+        let arch_mem = T::new(&mut page_manager);
 
-        Self { page_manager, arch }
+        Self { page_manager, arch: arch_mem }
     }
 
     fn map(&mut self, to: usize, from: usize, perms: Permissions) {

src/mm/page_manager.rs

@@ -2,6 +2,7 @@ use super::page_alloc::{AllocatorError, PageAllocator};
 use crate::kprintln;
 use crate::mm;
 use core::mem;
+use crate::Architecture;
 
 #[derive(Debug, PartialEq)]
 pub enum PageKind {
@@ -55,18 +56,19 @@ pub struct PageManager<'a> {
 
 impl<'a> PageManager<'a> {
     fn count_pages(
-        regions: impl Iterator<Item = fdt::standard_nodes::MemoryRegion>,
+        arch: &impl Architecture,
         page_size: usize,
     ) -> usize {
-        regions
-            .map(|region| {
-                (region.starting_address, unsafe {
-                    region.starting_address.add(region.size.unwrap_or(0))
-                })
-            })
-            .map(|(start, end)| (start as usize, end as usize))
-            .flat_map(|(start, end)| (start..end).step_by(page_size))
-            .count()
+        let mut count = 0;
+
+        arch.for_all_memory_regions(|regions| {
+            count = regions
+                .map(|(start, end)| (start as usize, end as usize))
+                .flat_map(|(start, end)| (start..end).step_by(page_size))
+                .count();
+        });
+
+        count
     }
 
     fn align_up(addr: usize, alignment: usize) -> usize {
@@ -75,12 +77,12 @@ impl<'a> PageManager<'a> {
 
     fn phys_addr_to_physical_page(
         phys_addr: usize,
-        device_tree: &fdt::Fdt,
+        arch: &impl Architecture,
         page_size: usize,
     ) -> PhysicalPage {
         let kind = if mm::is_kernel_page(phys_addr) {
             PageKind::Kernel
-        } else if mm::is_reserved_page(phys_addr, device_tree) {
+        } else if mm::is_reserved_page(phys_addr, arch) {
             PageKind::Reserved
         } else {
             PageKind::Unused
@@ -96,44 +98,42 @@ impl<'a> PageManager<'a> {
     /// Look for `pages_needed` contiguous unused pages, beware of pages that are in use by the
     /// kernel.
     fn find_contiguous_unused_pages(
-        device_tree: &fdt::Fdt,
+        arch: &impl Architecture,
         pages_needed: usize,
         page_size: usize,
     ) -> Option<usize> {
-        let memory = device_tree.memory();
-
-        let physical_pages = memory
-            .regions()
-            .map(|region| {
-                (region.starting_address, unsafe {
-                    region.starting_address.add(region.size.unwrap_or(0))
-                })
-            })
-            .map(|(start, end)| (start as usize, end as usize))
-            .flat_map(|(start, end)| (start..end).step_by(page_size))
-            .map(|base| Self::phys_addr_to_physical_page(base, device_tree, page_size));
-
-        let mut first_page_addr: usize = 0;
-        let mut consecutive_pages: usize = 0;
+        let mut found = None;
 
-        for page in physical_pages {
-            if consecutive_pages == 0 {
-                first_page_addr = page.base;
-            }
+        arch.for_all_memory_regions(|regions| {
+            let physical_pages = regions
+                .flat_map(|(start, end)| (start..end).step_by(page_size))
+                .map(|base| Self::phys_addr_to_physical_page(base, arch, page_size));
 
-            if page.is_used() {
-                consecutive_pages = 0;
-                continue;
-            }
+            let mut first_page_addr: usize = 0;
+            let mut consecutive_pages: usize = 0;
 
-            consecutive_pages += 1;
+            for page in physical_pages {
+                if consecutive_pages == 0 {
+                    first_page_addr = page.base;
+                }
+
+                if page.is_used() {
+                    consecutive_pages = 0;
+                    continue;
+                }
 
-            if consecutive_pages == pages_needed {
-                return Some(first_page_addr);
+                consecutive_pages += 1;
+
+                if consecutive_pages == pages_needed {
+                    found = Some(first_page_addr);
+                    return
+                }
             }
-        }
 
-        None
+            return;
+        });
+
+        found
     }
 
     /// TLDR: Initialize a [`PageAllocator`] from the device tree.
@@ -143,42 +143,36 @@ impl<'a> PageManager<'a> {
     /// - Second (in [`Self::find_contiguous_unused_pages`]), look through our pages for a contiguous
     /// space large enough to hold all our metadata.
     /// - Lastly store our metadata there, and mark pages as unused or kernel.
-    pub fn from_device_tree(device_tree: &fdt::Fdt, page_size: usize) -> Self {
-        let memory_node = device_tree.memory();
-
-        let page_count = Self::count_pages(memory_node.regions(), page_size);
+    pub fn from_arch_info(arch: &impl Architecture, page_size: usize) -> Self {
+        let page_count = Self::count_pages(arch, page_size);
         let metadata_size = page_count * mem::size_of::<PhysicalPage>();
         let pages_needed = Self::align_up(metadata_size, page_size) / page_size;
         kprintln!("total of {:?} pages", page_count);
         kprintln!("metadata_size: {:?}", metadata_size);
         kprintln!("pages_needed: {:?}", pages_needed);
 
         let metadata_addr =
-            Self::find_contiguous_unused_pages(device_tree, pages_needed, page_size).unwrap();
+            Self::find_contiguous_unused_pages(arch, pages_needed, page_size).unwrap();
         kprintln!("metadata_addr: {:X}", metadata_addr);
 
         let metadata: &mut [PhysicalPage] =
             unsafe { core::slice::from_raw_parts_mut(metadata_addr as *mut _, page_count) };
 
-        let physical_pages = memory_node
-            .regions()
-            .map(|region| {
-                (region.starting_address, unsafe {
-                    region.starting_address.add(region.size.unwrap_or(0))
-                })
-            })
-            .map(|(start, end)| (start as usize, end as usize))
-            .flat_map(|(start, end)| (start..end).step_by(page_size))
-            .map(|base| Self::phys_addr_to_physical_page(base, device_tree, page_size));
-
-        for (i, page) in physical_pages.enumerate() {
-            metadata[i] = page;
-        }
+        arch.for_all_memory_regions(|regions| {
+            let physical_pages = regions
+                .flat_map(|(start, end)| (start..end).step_by(page_size))
+                .map(|base| Self::phys_addr_to_physical_page(base, arch, page_size));
 
-        return Self {
+            for (i, page) in physical_pages.enumerate() {
+                metadata[i] = page;
+            }
+        });
+
+
+        Self {
             metadata,
             page_size,
-        };
+        }
     }
 
     pub fn page_size(&self) -> usize {