From 2b8ade8a1321f2d83e0317367a3bd107759bae40 Mon Sep 17 00:00:00 2001
From: tsatke <tim.satke@gmail.com>
Date: Sat, 22 Jun 2024 22:40:57 +0200
Subject: [PATCH] add support for growing files with writes that need to
 allocate new blocks

---
 ext2/src/bytefield.rs | 18 ++++++++++++++++++
 ext2/src/inode.rs     | 37 ++++++++++---------------------------
 ext2/src/write.rs     | 26 ++++++++++++++++++--------
 3 files changed, 46 insertions(+), 35 deletions(-)

diff --git a/ext2/src/bytefield.rs b/ext2/src/bytefield.rs
index 81bba2b..c2039d0 100644
--- a/ext2/src/bytefield.rs
+++ b/ext2/src/bytefield.rs
@@ -33,6 +33,18 @@ macro_rules! bytefield_field_read {
             t
         }
     };
+    ([u32; $len:literal], $offset:literal, $source:expr) => { $crate::bytefield_field_read!(u32_array [u32; $len], $offset, $source) };
+    (u32_array $typ:ty, $offset:literal, $source:expr) => {
+        {
+            check_is_implemented!($typ, Default);
+            let mut t: $typ = Default::default();
+            let source_bytes = &$source[$offset..$offset + core::mem::size_of::<$typ>()];
+            source_bytes.chunks_exact(4).enumerate().for_each(|(i, chunk)| {
+                t[i] = u32::from_le_bytes(chunk.try_into().unwrap());
+            });
+            t
+        }
+    };
 }
 
 #[macro_export]
@@ -51,6 +63,12 @@ macro_rules! bytefield_field_write {
     (u8_array $typ:ty, $field:expr, $offset:literal, $target:expr) => {
         $target[$offset..$offset + core::mem::size_of::<$typ>()].copy_from_slice(&$field);
     };
+    ([u32; $len:literal], $field:expr, $offset:literal, $target:expr) => { $crate::bytefield_field_write!(u32_array [u32; $len], $field, $offset, $target) };
+    (u32_array $typ:ty, $field:expr, $offset:literal, $target:expr) => {
+        let field = $field;
+        let aligned = unsafe { field.align_to::<u8>().1 };
+        $target[$offset..$offset + core::mem::size_of::<$typ>()].copy_from_slice(&aligned);
+    };
 }
 
 #[macro_export]
diff --git a/ext2/src/inode.rs b/ext2/src/inode.rs
index ffd3906..36afb4e 100644
--- a/ext2/src/inode.rs
+++ b/ext2/src/inode.rs
@@ -115,18 +115,7 @@ bytefield! {
         num_disk_sectors: u32 = 28,
         flags: u32 = 32,
         os_val_1: [u8; 4] = 36,
-        direct_block_ptr_0: u32 = 40,
-        direct_block_ptr_1: u32 = 44,
-        direct_block_ptr_2: u32 = 48,
-        direct_block_ptr_3: u32 = 52,
-        direct_block_ptr_4: u32 = 56,
-        direct_block_ptr_5: u32 = 60,
-        direct_block_ptr_6: u32 = 64,
-        direct_block_ptr_7: u32 = 68,
-        direct_block_ptr_8: u32 = 72,
-        direct_block_ptr_9: u32 = 76,
-        direct_block_ptr_10: u32 = 80,
-        direct_block_ptr_11: u32 = 84,
+        direct_block_ptr: [u32; 12] = 40,
         singly_indirect_block_ptr: u32 = 88,
         doubly_indirect_block_ptr: u32 = 92,
         triply_indirect_block_ptr: u32 = 96,
@@ -160,21 +149,15 @@ impl Inode {
     }
 
     pub fn direct_ptr(&self, index: usize) -> Option<BlockAddress> {
-        BlockAddress::new(match index {
-            0 => self.direct_block_ptr_0,
-            1 => self.direct_block_ptr_1,
-            2 => self.direct_block_ptr_2,
-            3 => self.direct_block_ptr_3,
-            4 => self.direct_block_ptr_4,
-            5 => self.direct_block_ptr_5,
-            6 => self.direct_block_ptr_6,
-            7 => self.direct_block_ptr_7,
-            8 => self.direct_block_ptr_8,
-            9 => self.direct_block_ptr_9,
-            10 => self.direct_block_ptr_10,
-            11 => self.direct_block_ptr_11,
-            _ => panic!("direct pointer {} does not exist", index),
-        })
+        BlockAddress::new(self.direct_block_ptr[index])
+    }
+
+    pub fn direct_ptrs(&self) -> impl Iterator<Item=Option<BlockAddress>> + '_ {
+        self.direct_block_ptr.iter().map(|&ptr| BlockAddress::new(ptr))
+    }
+
+    pub fn set_direct_ptr(&mut self, index: usize, ptr: Option<BlockAddress>) {
+        self.direct_block_ptr[index] = ptr.map_or(0, |v| v.into_u32());
     }
 
     pub fn single_indirect_ptr(&self) -> Option<BlockAddress> {
diff --git a/ext2/src/write.rs b/ext2/src/write.rs
index 59d9363..baaa17a 100644
--- a/ext2/src/write.rs
+++ b/ext2/src/write.rs
@@ -36,14 +36,24 @@ where
 
         for (i, block) in (start_block..=end_block).enumerate() {
             if !self.is_block_allocated(file, block)? {
-                todo!("allocate block")
-                // // TODO: we don't need to allocate if the full content of this block would be zero if the fs allows sparse files
-                // let free_block_address = self.allocate_block()?;
-                // if free_block_address.is_none() {
-                //     return Err(Error::NoSpace);
-                // }
-                // let free_block_address = free_block_address.unwrap();
-                // // TODO: write the block address to the inode
+                // TODO: we don't need to allocate if the full content of this block would be zero if the fs allows sparse files
+                let free_block_address = self.allocate_block()?;
+                if free_block_address.is_none() {
+                    return Err(Error::NoSpace);
+                }
+                let free_block_address = free_block_address.unwrap();
+
+                let inode = file.inode_mut();
+                let free_slot = inode.direct_ptrs()
+                    .enumerate()
+                    .find(|(_, ptr)| ptr.is_none())
+                    .map(|(i, _)| i);
+                if let Some(free_slot) = free_slot {
+                    inode.set_direct_ptr(free_slot, Some(free_block_address));
+                    self.write_inode(file.inode_address(), file)?;
+                } else {
+                    todo!("allocate indirect block");
+                }
             }
         }