add block group descriptor table loading to Ext2 struct

src/fs.rs

@@ -1,6 +1,9 @@
+use alloc::Vec;
+
 use error::Error;
 use buffer::{Buffer, BufferSlice};
 use sys::superblock::Superblock;
+use sys::block_group::BlockGroupDescriptor;
 
 struct Struct<T> {
     pub inner: T,
@@ -18,6 +21,7 @@ impl<T> From<(T, usize)> for Struct<T> {
 pub struct Ext2<B: Buffer<u8>> {
     buffer: B,
     superblock: Struct<Superblock>,
+    block_groups: Struct<Vec<BlockGroupDescriptor>>,
 }
 
 impl<B: Buffer<u8>> Ext2<B>
@@ -25,8 +29,26 @@ where
     Error: From<B::Error>,
 {
     pub fn new(buffer: B) -> Result<Ext2<B>, Error> {
-        let superblock = Superblock::find(&buffer)?.into();
-        Ok(Ext2 { buffer, superblock })
+        let superblock = Struct::from(Superblock::find(&buffer)?);
+        let block_size = superblock.inner.block_size();
+        let block_groups_offset =
+            (superblock.inner.first_data_block as usize + 1) * block_size;
+        let block_groups_count = superblock
+            .inner
+            .block_group_count()
+            .map(|count| count as usize)
+            .map_err(|(a, b)| Error::BadBlockGroupCount(a, b))?;
+        let block_groups = BlockGroupDescriptor::find_descriptor_table(
+            &buffer,
+            block_groups_offset,
+            block_groups_count,
+        )?;
+        let block_groups = Struct::from(block_groups);
+        Ok(Ext2 {
+            buffer,
+            superblock,
+            block_groups,
+        })
     }
 
     pub fn update(&mut self) -> Result<(), Error> {
@@ -46,6 +68,13 @@ where
         &mut self.superblock.inner
     }
 
+    pub fn block_group_count(&self) -> Result<usize, Error> {
+        self.superblock()
+            .block_group_count()
+            .map(|count| count as usize)
+            .map_err(|(a, b)| Error::BadBlockGroupCount(a, b))
+    }
+
     pub fn total_block_count(&self) -> usize {
         self.superblock().blocks_count as _
     }