move a lot of logic into this lib

Author: tsatke

ext2/src/error.rs

@@ -12,6 +12,7 @@ pub enum Error {
     DeviceRead,
     DeviceWrite,
     InvalidInodeAddress(u32),
+    NoSpace,
 }
 
 impl Display for Error {

ext2/src/file.rs

@@ -1,5 +1,6 @@
 #![no_std]
 #![feature(const_option)]
+#![feature(iter_array_chunks)]
 
 extern crate alloc;
 
@@ -8,7 +9,6 @@ use alloc::vec;
 pub use address::*;
 pub use dir::*;
 pub use error::*;
-pub use file::*;
 use filesystem::BlockDevice;
 pub use inode::*;
 pub use superblock::*;
@@ -20,9 +20,10 @@ mod block_group;
 mod bytefield;
 mod dir;
 mod error;
-mod file;
+mod read;
 mod inode;
 mod superblock;
+mod write;
 
 const ROOT_DIR_INODE_ADDRESS: InodeAddress = InodeAddress::new(2).unwrap();
 

ext2/src/lib.rs

@@ -0,0 +1,137 @@
+use alloc::vec;
+use alloc::vec::Vec;
+
+use filesystem::BlockDevice;
+
+use crate::{BlockAddress, Error, Ext2Fs, Inode, RegularFile};
+
+const SZ: usize = size_of::<BlockAddress>();
+
+impl<T> Ext2Fs<T>
+where
+    T: BlockDevice,
+{
+    pub fn read_from_file(
+        &self,
+        file: &RegularFile,
+        offset: usize,
+        buf: &mut [u8],
+    ) -> Result<usize, Error> {
+        let file_size = file.len();
+        if offset >= file_size {
+            return Ok(0);
+        }
+
+        let block_size = self.superblock.block_size();
+        let offset = offset as u32;
+
+        let start_block = offset / block_size;
+        let end_block = (offset + buf.len() as u32 - 1) / block_size;
+        let relative_offset = (offset % block_size) as usize;
+        let block_count = (end_block - start_block + 1) as usize;
+
+        // read blocks
+        let mut data: Vec<u8> = vec![0_u8; block_count * block_size as usize]; // TODO: avoid allocation - maybe try to only allocate the first and last block if the read is not aligned, but read the rest directly into the buffer
+        let res = self.read_blocks_from_inode(file, start_block as usize, end_block as usize, &mut data)?;
+        // copy the data into buf, but only the requested part and only up to the file size
+        let total_read = res.min(file_size - offset as usize).min(buf.len());
+        buf[..total_read].copy_from_slice(&data[relative_offset..relative_offset + total_read]);
+
+
+        Ok(total_read)
+    }
+
+    fn read_blocks_from_inode(&self, inode: &Inode, start_block: usize, end_block: usize, buf: &mut [u8]) -> Result<usize, Error> {
+        let block_size = self.superblock.block_size() as usize;
+        assert_eq!(buf.len(), (end_block - start_block + 1) * block_size, "buf.len() must be equal to the number of blocks you want to read");
+
+        let (direct_limit, indirect_limit, double_indirect_limit) = self.indirect_pointer_limits();
+
+        let mut total_read = 0;
+
+        for (i, block) in (start_block..=end_block).enumerate() {
+            let block_data = &mut buf[i * block_size..(i + 1) * block_size];
+            let block_pointer = if block < direct_limit as usize {
+                inode.direct_ptr(block)
+            } else if block < indirect_limit as usize {
+                self.resolve_indirect_ptr(inode.single_indirect_ptr(), block as u32 - direct_limit)?
+            } else if block < double_indirect_limit as usize {
+                self.resolve_double_indirect_ptr(inode.double_indirect_ptr(), block as u32 - indirect_limit)?
+            } else {
+                self.resolve_triple_indirect_ptr(inode.triple_indirect_ptr(), block as u32 - double_indirect_limit)?
+            };
+            if let Some(block_pointer) = block_pointer {
+                total_read += self.read_block(block_pointer, block_data)?;
+            } else {
+                block_data.fill(0);
+                total_read += block_size; // FIXME: what if the last block is sparse?
+            }
+        }
+
+        Ok(total_read)
+    }
+
+    pub fn indirect_pointer_limits(&self) -> (u32, u32, u32) {
+        let direct_limit = 12;
+        let indirect_limit = direct_limit + self.superblock.block_size() / 4;
+        let double_indirect_limit = indirect_limit + indirect_limit * indirect_limit;
+        (direct_limit, indirect_limit, double_indirect_limit)
+    }
+
+    pub fn is_block_allocated(&self, inode: &Inode, block_index: u32) -> Result<bool, Error> {
+        let (direct_limit, indirect_limit, double_indirect_limit) = self.indirect_pointer_limits();
+
+        Ok(
+            if block_index < direct_limit {
+                inode.direct_ptr(block_index as usize)
+            } else if block_index < indirect_limit {
+                self.resolve_indirect_ptr(inode.single_indirect_ptr(), block_index - direct_limit)?
+            } else if block_index < double_indirect_limit {
+                self.resolve_double_indirect_ptr(inode.double_indirect_ptr(), block_index - indirect_limit)?
+            } else {
+                self.resolve_triple_indirect_ptr(inode.triple_indirect_ptr(), block_index - double_indirect_limit)?
+            }
+                .is_some()
+        )
+    }
+
+    pub fn resolve_indirect_ptr(&self, indirect_ptr: Option<BlockAddress>, block_index: u32) -> Result<Option<BlockAddress>, Error> {
+        if indirect_ptr.is_none() {
+            return Ok(None);
+        }
+        let indirect_ptr = indirect_ptr.unwrap();
+
+        let mut indirect_block_data = vec![0_u8; self.superblock.block_size() as usize];
+        self.read_block(indirect_ptr, &mut indirect_block_data)?;
+        Ok(
+            indirect_block_data
+                .iter()
+                .copied()
+                .array_chunks::<SZ>()
+                .map(u32::from_le_bytes)
+                .map(BlockAddress::new)
+                .nth(block_index as usize)
+                .unwrap() // the amount of pointers is fixed, so this is fine
+        )
+    }
+
+    pub fn resolve_double_indirect_ptr(&self, double_indirect_block: Option<BlockAddress>, block_index: u32) -> Result<Option<BlockAddress>, Error> {
+        let block_size = self.superblock.block_size();
+
+        let single_indirect_block_size = block_size / 4;
+        let single_indirect_index = block_index / single_indirect_block_size;
+
+        self.resolve_indirect_ptr(double_indirect_block, single_indirect_index)
+            .and_then(|single_indirect_block_ptr| self.resolve_indirect_ptr(single_indirect_block_ptr, block_index % single_indirect_block_size))
+    }
+
+    pub fn resolve_triple_indirect_ptr(&self, triple_indirect_block: Option<BlockAddress>, block_index: u32) -> Result<Option<BlockAddress>, Error> {
+        let block_size = self.superblock.block_size();
+
+        let double_indirect_block_size = block_size / 4;
+        let double_indirect_index = block_index / double_indirect_block_size;
+
+        self.resolve_indirect_ptr(triple_indirect_block, double_indirect_index)
+            .and_then(|double_indirect_block_ptr| self.resolve_double_indirect_ptr(double_indirect_block_ptr, block_index % double_indirect_block_size))
+    }
+}

ext2/src/read.rs

@@ -0,0 +1,42 @@
+use filesystem::BlockDevice;
+
+use crate::{Error, Ext2Fs, RegularFile};
+
+impl<T> Ext2Fs<T>
+where
+    T: BlockDevice,
+{
+    #[allow(unused_variables)]
+    pub fn write_to_file(
+        &mut self,
+        file: &RegularFile,
+        offset: usize,
+        buf: &[u8],
+    ) -> Result<usize, Error> {
+        let block_size = self.superblock.block_size();
+        let offset = offset as u32;
+
+        let start_block = offset / block_size;
+        let end_block = (offset + buf.len() as u32 - 1) / block_size;
+        let relative_offset = (offset % block_size) as usize;
+        let block_count = (end_block - start_block + 1) as usize;
+
+        assert_eq!(buf.len() % block_size as usize, 0, "buf.len() must be a multiple of block_size for now"); // TODO: make this more flexible
+
+        for (i, block) in (start_block..=end_block).enumerate() {
+            if !self.is_block_allocated(file, 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
+            }
+        }
+
+        // we can now be certain that all blocks that we want to write into are allocated
+
+        todo!()
+    }
+}