Implement dir ops and inode ops in Rust.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
 fs/erofs/rust/erofs_sys.rs            |  1 +
 fs/erofs/rust/erofs_sys/data.rs       |  4 ++
 fs/erofs/rust/erofs_sys/operations.rs | 35 ++++++++++++++++
 fs/erofs/rust/erofs_sys/superblock.rs | 59 +++++++++++++++++++++++++++
 4 files changed, 99 insertions(+)
 create mode 100644 fs/erofs/rust/erofs_sys/operations.rs

diff --git a/fs/erofs/rust/erofs_sys.rs b/fs/erofs/rust/erofs_sys.rs
index 20c0aa81a800..8c08ac347b2b 100644
--- a/fs/erofs/rust/erofs_sys.rs
+++ b/fs/erofs/rust/erofs_sys.rs
@@ -30,6 +30,7 @@
 pub(crate) mod errnos;
 pub(crate) mod inode;
 pub(crate) mod map;
+pub(crate) mod operations;
 pub(crate) mod superblock;
 pub(crate) mod xattrs;
 pub(crate) use errnos::{Errno, Errno::*};
diff --git a/fs/erofs/rust/erofs_sys/data.rs b/fs/erofs/rust/erofs_sys/data.rs
index 21630673c24e..67bb66ce9efb 100644
--- a/fs/erofs/rust/erofs_sys/data.rs
+++ b/fs/erofs/rust/erofs_sys/data.rs
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: MIT or GPL-2.0-or-later
 pub(crate) mod backends;
 pub(crate) mod raw_iters;
+use super::dir::*;
 use super::inode::*;
 use super::map::*;
 use super::superblock::*;
@@ -26,6 +27,9 @@ pub(crate) trait Backend {
 /// DirEntries.
 pub(crate) trait Buffer {
     fn content(&self) -> &[u8];
+    fn iter_dir(&self) -> DirCollection<'_> {
+        DirCollection::new(self.content())
+    }
 }
 
 /// Represents a buffer that holds a reference to a slice of data that
diff --git a/fs/erofs/rust/erofs_sys/operations.rs b/fs/erofs/rust/erofs_sys/operations.rs
new file mode 100644
index 000000000000..070ba20908a2
--- /dev/null
+++ b/fs/erofs/rust/erofs_sys/operations.rs
@@ -0,0 +1,35 @@
+// Copyright 2024 Yiyang Wu
+// SPDX-License-Identifier: MIT or GPL-2.0-or-later
+
+use super::inode::*;
+use super::superblock::*;
+use super::*;
+
+pub(crate) fn read_inode<'a, I, C>(
+    filesystem: &'a dyn FileSystem<I>,
+    collection: &'a mut C,
+    nid: Nid,
+) -> PosixResult<&'a mut I>
+where
+    I: Inode,
+    C: InodeCollection<I = I>,
+{
+    collection.iget(nid, filesystem)
+}
+
+pub(crate) fn dir_lookup<'a, I, C>(
+    filesystem: &'a dyn FileSystem<I>,
+    collection: &'a mut C,
+    inode: &I,
+    name: &str,
+) -> PosixResult<&'a mut I>
+where
+    I: Inode,
+    C: InodeCollection<I = I>,
+{
+    filesystem
+        .find_nid(inode, name)?
+        .map_or(Err(Errno::ENOENT), |nid| {
+            read_inode(filesystem, collection, nid)
+        })
+}
diff --git a/fs/erofs/rust/erofs_sys/superblock.rs b/fs/erofs/rust/erofs_sys/superblock.rs
index f60657eff3d6..403ffdeb4573 100644
--- a/fs/erofs/rust/erofs_sys/superblock.rs
+++ b/fs/erofs/rust/erofs_sys/superblock.rs
@@ -8,6 +8,7 @@
 use super::data::raw_iters::*;
 use super::data::*;
 use super::devices::*;
+use super::dir::*;
 use super::inode::*;
 use super::map::*;
 use super::*;
@@ -287,6 +288,64 @@ fn continuous_iter<'a>(
         offset: Off,
         len: Off,
     ) -> PosixResult<Box<dyn ContinuousBufferIter<'a> + 'a>>;
+
+    // Inode related goes here.
+    fn read_inode_info(&self, nid: Nid) -> PosixResult<InodeInfo> {
+        (self.as_filesystem(), nid).try_into()
+    }
+
+    fn find_nid(&self, inode: &I, name: &str) -> PosixResult<Option<Nid>> {
+        for buf in self.mapped_iter(inode, 0)? {
+            for dirent in buf?.iter_dir() {
+                if dirent.dirname() == name.as_bytes() {
+                    return Ok(Some(dirent.desc.nid));
+                }
+            }
+        }
+        Ok(None)
+    }
+
+    // Readdir related goes here.
+    fn fill_dentries(
+        &self,
+        inode: &I,
+        offset: Off,
+        emitter: &mut dyn FnMut(Dirent<'_>, Off),
+    ) -> PosixResult<()> {
+        let sb = self.superblock();
+        let accessor = sb.blk_access(offset);
+        if offset > inode.info().file_size() {
+            return Err(EUCLEAN);
+        }
+
+        let map_offset = round!(DOWN, offset, sb.blksz());
+        let blk_offset = round!(UP, accessor.off, size_of::<DirentDesc>() as Off);
+
+        let mut map_iter = self.mapped_iter(inode, map_offset)?;
+        let first_buf = map_iter.next().unwrap()?;
+        let mut collection = first_buf.iter_dir();
+
+        let mut pos: Off = map_offset + blk_offset;
+
+        if blk_offset as usize / size_of::<DirentDesc>() <= collection.total() {
+            collection.skip_dir(blk_offset as usize / size_of::<DirentDesc>());
+            for dirent in collection {
+                emitter(dirent, pos);
+                pos += size_of::<DirentDesc>() as Off;
+            }
+        }
+
+        pos = round!(UP, pos, sb.blksz());
+
+        for buf in map_iter {
+            for dirent in buf?.iter_dir() {
+                emitter(dirent, pos);
+                pos += size_of::<DirentDesc>() as Off;
+            }
+            pos = round!(UP, pos, sb.blksz());
+        }
+        Ok(())
+    }
 }
 
 pub(crate) struct SuperblockInfo<I, C, T>
-- 
2.46.0