ext2: add a simple unlink()

kernel/driver/fs/ext2/src/dir.rs

@@ -1,9 +1,15 @@
-use core::{any::Any, mem::MaybeUninit, str::FromStr};
+// TODO: dedupe the code for iterating the directory records
+use core::{
+    any::Any,
+    mem::{self, MaybeUninit},
+    str::FromStr,
+};
 
 use alloc::sync::Arc;
 use libk::{
     block,
     error::Error,
+    time::real_time,
     vfs::{CommonImpl, DirectoryImpl, DirectoryOpenPosition, Metadata, Node, NodeFlags, NodeRef},
 };
 use yggdrasil_abi::{
@@ -30,11 +36,117 @@ struct DirentIterMut<'a> {
     offset: usize,
 }
 
+struct Record<'a> {
+    fs: &'a Ext2Fs,
+    offset: usize,
+    data: &'a mut [u8],
+}
+
+impl Record<'_> {
+    pub fn dirent(&self) -> &Dirent {
+        bytemuck::from_bytes(&self.data[..size_of::<Dirent>()])
+    }
+
+    pub fn dirent_mut(&mut self) -> &mut Dirent {
+        bytemuck::from_bytes_mut(&mut self.data[..size_of::<Dirent>()])
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.dirent().ino == 0
+    }
+
+    pub fn ino(&self) -> u32 {
+        self.dirent().ino
+    }
+
+    fn name_len(&self) -> usize {
+        let len = self.dirent().name_length_low as usize;
+        if !self
+            .fs
+            .required_features
+            .contains(FsRequiredFeatures::DIRENT_TYPE_FIELD)
+        {
+            todo!();
+        }
+        len
+    }
+
+    fn name_bytes(&self) -> &[u8] {
+        if !self.is_empty() {
+            &self.data[size_of::<Dirent>()..size_of::<Dirent>() + self.name_len()]
+        } else {
+            b""
+        }
+    }
+
+    fn name(&self) -> Option<&str> {
+        core::str::from_utf8(self.name_bytes()).ok()
+    }
+
+    pub fn data_size(&self) -> usize {
+        // Whole dirent is free space
+        if self.is_empty() {
+            return 0;
+        }
+
+        self.name_len() + size_of::<Dirent>()
+    }
+
+    pub fn record_size(&self) -> usize {
+        (self.dirent().ent_size as usize).max(size_of::<Dirent>())
+    }
+
+    pub fn free_space(&self) -> usize {
+        self.data.len().saturating_sub(self.data_size())
+    }
+}
+
 impl<'a> DirentIterMut<'a> {
     pub fn new(fs: &'a Ext2Fs, block: &'a mut [u8], offset: usize) -> Self {
         Self { fs, block, offset }
     }
 
+    fn next_record(&mut self) -> Option<Record> {
+        if self.offset + size_of::<Dirent>() > self.block.len() {
+            return None;
+        }
+
+        let dirent_struct_end = self.offset + size_of::<Dirent>();
+        let dirent: &Dirent = bytemuck::from_bytes(&self.block[self.offset..dirent_struct_end]);
+        let record_size = (dirent.ent_size as usize).max(size_of::<Dirent>());
+        let record = Record {
+            data: &mut self.block[self.offset..self.offset + record_size],
+            fs: self.fs,
+            offset: self.offset,
+        };
+
+        self.offset += record_size;
+        Some(record)
+    }
+
+    pub fn remove(&mut self, search: &str) -> Option<u32> {
+        if search.is_empty() || search == "." || search == ".." {
+            return None;
+        }
+
+        let mut ino = None;
+        while let Some(mut record) = self.next_record() {
+            if record.name_bytes() != search.as_bytes() {
+                continue;
+            }
+
+            let dirent = record.dirent_mut();
+            ino = Some(mem::replace(&mut dirent.ino, 0));
+            break;
+        }
+
+        let ino = ino?;
+
+        // TODO compact the block
+
+        Some(ino)
+    }
+
     pub fn try_fit(&mut self, name: &str, ino: u32) -> bool {
         let _ = self.fs;
 
@@ -185,6 +297,7 @@ impl DirectoryNode {
                 let mut child = holder.write();
 
                 child.inc_hard_count();
+                child.dtime = 0;
             }
 
             holder.put().await?;
@@ -263,6 +376,53 @@ impl DirectoryNode {
         Ok(())
     }
 
+    async fn remove_entry(&self, name: &str) -> Result<(), Error> {
+        // TODO if unlinking a directory, check that it only contains . and ..
+        assert!(name.len() < 255);
+
+        let ino = {
+            let mut holder = self.inode.get_mut().await?;
+            let mut result = None;
+
+            {
+                let inode = holder.write();
+                let n = inode.blocks(&self.fs);
+
+                for i in 0..n {
+                    let ino = self
+                        .fs
+                        .with_inode_block_mut(&inode, i as _, 0, |block| {
+                            let mut iter = DirentIterMut::new(&self.fs, block, 0);
+                            Ok(iter.remove(name))
+                        })
+                        .await?;
+
+                    if let Some(ino) = ino {
+                        result = Some(ino);
+                        break;
+                    }
+                }
+            }
+            holder.put().await?;
+
+            result
+        };
+
+        let ino = ino.ok_or(Error::DoesNotExist)?;
+        log::info!("ext2: unlinked ino #{ino}");
+
+        // Decrement the refcount on the inode
+        let mut holder = self.inode.cache().get_mut(ino).await?;
+        {
+            let mut inode = holder.write();
+            inode.hard_links = inode.hard_links.saturating_sub(1);
+            inode.dtime = real_time().seconds as _;
+        }
+        holder.put().await?;
+
+        Ok(())
+    }
+
     async fn lookup_entry(&self, search_name: &str) -> Result<NodeRef, Error> {
         assert!(search_name.len() < 255);
 
@@ -416,12 +576,11 @@ impl DirectoryImpl for DirectoryNode {
         Ok(())
     }
 
-    fn unlink_node(&self, _parent: &NodeRef, _name: &str) -> Result<(), Error> {
+    fn unlink_node(&self, _parent: &NodeRef, name: &str) -> Result<(), Error> {
         if self.fs.force_readonly {
             return Err(Error::ReadOnly);
         }
-        log::error!("ext2: unlink_node not implemented");
-        Err(Error::NotImplemented)
+        block!(self.remove_entry(name).await)?
     }
 
     fn read_entries(