ext2: Support longer symlinks

Symbolic links that are longer than or equal to 60 bytes require
a block allocated to store its destination because it won't fit
in Inode's i_block.

BUG=b:342937495
TEST=cargo test

Change-Id: Iadab10887c136019fe85e74fa981542384f48ad2
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/5569438
Reviewed-by: Junichi Uekawa <uekawa@chromium.org>
Commit-Queue: Keiichi Watanabe <keiichiw@chromium.org>

ext2/src/fs.rs

@@ -558,8 +558,7 @@ impl<'a> Ext2<'a> {
             .context("failed to convert symlink destination to str")?;
 
         if dst.len() >= InodeBlock::max_inline_symlink_len() {
-            // TODO(b/342937495): Support symlink longer than or equal to 60 bytes.
-            unimplemented!("long symlink is not supported yet: {:?}", dst);
+            return self.add_long_symlink(arena, parent, &link, dst);
         }
 
         let inode_num = self.allocate_inode()?;
@@ -584,6 +583,46 @@ impl<'a> Ext2<'a> {
         Ok(())
     }
 
+    fn add_long_symlink(
+        &mut self,
+        arena: &'a Arena<'a>,
+        parent: InodeNum,
+        link: &Path,
+        dst: &str,
+    ) -> Result<()> {
+        let dst_len = dst.len();
+        if dst_len > self.block_size() as usize {
+            bail!("symlink longer than block size: {:?}", dst);
+        }
+
+        // Copy symlink's destination to the block.
+        let symlink_block = self.allocate_block()?;
+        let buf = arena.allocate_slice(symlink_block, 0, dst_len)?;
+        buf.copy_from_slice(dst.as_bytes());
+
+        let inode_num = self.allocate_inode()?;
+        let mut block = InodeBlock::default();
+        block.set_direct_blocks(&[symlink_block])?;
+
+        let block_size = self.block_size() as u32;
+        let inode = Inode::from_metadata(
+            arena,
+            &mut self.group_metadata,
+            inode_num,
+            &std::fs::symlink_metadata(link)?,
+            dst_len as u32,
+            1, //links_count,
+            InodeBlocksCount::from_bytes_len(block_size),
+            block,
+        )?;
+        self.add_inode(inode_num, inode)?;
+
+        let link_name = link.file_name().context("failed to get symlink name")?;
+        self.allocate_dir_entry(arena, parent, inode_num, InodeType::Symlink, link_name)?;
+
+        Ok(())
+    }
+
     /// Walks through `src_dir` and copies directories and files to the new file system.
     fn copy_dirtree<P: AsRef<Path>>(&mut self, arena: &'a Arena<'a>, src_dir: P) -> Result<()> {
         self.copy_dirtree_rec(arena, InodeNum(2), src_dir)

ext2/src/inode.rs

@@ -152,7 +152,6 @@ impl InodeBlock {
                 Self::max_inline_symlink_len()
             );
         }
-
         self.0[..bytes.len()].copy_from_slice(bytes);
         Ok(())
     }

ext2/tests/tests.rs

@@ -426,3 +426,43 @@ fn test_mkfs_symlink_to_deleted() {
 
     assert_eq_dirs(&td, &dir, &disk);
 }
+
+#[test]
+fn test_mkfs_long_symlink() {
+    // testdata
+    // ├── /(long name directory)/a.txt
+    // └── symlink -> /(long name directory)/a.txt
+    // ├── (60-byte filename)
+    // └── symlink60 -> (60-byte filename)
+
+    let td = tempdir().unwrap();
+    let dir = td.path().join("testdata");
+
+    create_dir(&dir).unwrap();
+
+    const LONG_DIR_NAME: &str =
+        "this_is_a_very_long_directory_name_so_that_name_cannoot_fit_in_60_characters_in_inode";
+    assert!(LONG_DIR_NAME.len() > 60);
+
+    let long_dir = dir.join(LONG_DIR_NAME);
+    create_dir(&long_dir).unwrap();
+    File::create(long_dir.join("a.txt")).unwrap();
+    symlink(long_dir.join("a.txt"), dir.join("symlink")).unwrap();
+
+    const SIXTY_CHAR_DIR_NAME: &str =
+        "./this_is_just_60_byte_long_so_it_can_work_as_a_corner_case.";
+    assert_eq!(SIXTY_CHAR_DIR_NAME.len(), 60);
+    File::create(dir.join(SIXTY_CHAR_DIR_NAME)).unwrap();
+    symlink(SIXTY_CHAR_DIR_NAME, dir.join("symlink60")).unwrap();
+
+    let disk = mkfs(
+        &td,
+        &Config {
+            blocks_per_group: 2048,
+            inodes_per_group: 4096,
+        },
+        Some(&dir),
+    );
+
+    assert_eq_dirs(&td, &dir, &disk);
+}