[RFC PATCH 15/24] erofs: add iter methods in filesystem in Rust

[Yiyang Wu <toolmanp@tlmp.cc>]

Implement mapped iter that uses the MapIter and can yield data that is
backed by EROFS inode.

Implement continuous_iter and mapped_iter for filesystem which can
returns an iterator that yields raw data.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
 fs/erofs/rust/erofs_sys/data.rs               |  2 +
 .../rust/erofs_sys/data/raw_iters/ref_iter.rs | 63 +++++++++++++++++++
 .../rust/erofs_sys/data/raw_iters/traits.rs   |  4 ++
 fs/erofs/rust/erofs_sys/superblock.rs         | 13 ++++
 fs/erofs/rust/erofs_sys/superblock/mem.rs     | 22 +++++++
 5 files changed, 104 insertions(+)

diff --git a/fs/erofs/rust/erofs_sys/data.rs b/fs/erofs/rust/erofs_sys/data.rs
index 483f3204ce42..21630673c24e 100644
--- a/fs/erofs/rust/erofs_sys/data.rs
+++ b/fs/erofs/rust/erofs_sys/data.rs
@@ -2,6 +2,8 @@
 // SPDX-License-Identifier: MIT or GPL-2.0-or-later
 pub(crate) mod backends;
 pub(crate) mod raw_iters;
+use super::inode::*;
+use super::map::*;
 use super::superblock::*;
 use super::*;
 
diff --git a/fs/erofs/rust/erofs_sys/data/raw_iters/ref_iter.rs b/fs/erofs/rust/erofs_sys/data/raw_iters/ref_iter.rs
index 5aa2b7f44f3d..d39c9523b628 100644
--- a/fs/erofs/rust/erofs_sys/data/raw_iters/ref_iter.rs
+++ b/fs/erofs/rust/erofs_sys/data/raw_iters/ref_iter.rs
@@ -4,6 +4,69 @@
 use super::super::*;
 use super::*;
 
+pub(crate) struct RefMapIter<'a, 'b, FS, B, I>
+where
+    FS: FileSystem<I>,
+    B: Backend,
+    I: Inode,
+{
+    sb: &'a SuperBlock,
+    backend: &'a B,
+    map_iter: MapIter<'a, 'b, FS, I>,
+}
+
+impl<'a, 'b, FS, B, I> RefMapIter<'a, 'b, FS, B, I>
+where
+    FS: FileSystem<I>,
+    B: Backend,
+    I: Inode,
+{
+    pub(crate) fn new(
+        sb: &'a SuperBlock,
+        backend: &'a B,
+        map_iter: MapIter<'a, 'b, FS, I>,
+    ) -> Self {
+        Self {
+            sb,
+            backend,
+            map_iter,
+        }
+    }
+}
+
+impl<'a, 'b, FS, B, I> Iterator for RefMapIter<'a, 'b, FS, B, I>
+where
+    FS: FileSystem<I>,
+    B: Backend,
+    I: Inode,
+{
+    type Item = PosixResult<RefBuffer<'a>>;
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.map_iter.next() {
+            Some(map) => match map {
+                Ok(m) => {
+                    let accessor = self.sb.blk_access(m.physical.start);
+                    let len = m.physical.len.min(accessor.len);
+                    match self.backend.as_buf(m.physical.start, len) {
+                        Ok(buf) => Some(Ok(buf)),
+                        Err(e) => Some(Err(e)),
+                    }
+                }
+                Err(e) => Some(Err(e)),
+            },
+            None => None,
+        }
+    }
+}
+
+impl<'a, 'b, FS, B, I> BufferMapIter<'a> for RefMapIter<'a, 'b, FS, B, I>
+where
+    FS: FileSystem<I>,
+    B: Backend,
+    I: Inode,
+{
+}
+
 /// Continous Ref Buffer Iterator which iterates over a range of disk addresses within the
 /// the temp block size. Since the temp block is always the same size as page and it will not
 /// overflow.
diff --git a/fs/erofs/rust/erofs_sys/data/raw_iters/traits.rs b/fs/erofs/rust/erofs_sys/data/raw_iters/traits.rs
index 90b6a51658a9..531e970cdb49 100644
--- a/fs/erofs/rust/erofs_sys/data/raw_iters/traits.rs
+++ b/fs/erofs/rust/erofs_sys/data/raw_iters/traits.rs
@@ -3,6 +3,10 @@
 
 use super::super::*;
 
+/// Represents a basic iterator over a range of bytes from data backends.
+/// The access order is guided by the block maps from the filesystem.
+pub(crate) trait BufferMapIter<'a>: Iterator<Item = PosixResult<RefBuffer<'a>>> {}
+
 /// Represents a basic iterator over a range of bytes from data backends.
 /// Note that this is skippable and can be used to move the iterator's cursor forward.
 pub(crate) trait ContinuousBufferIter<'a>:
diff --git a/fs/erofs/rust/erofs_sys/superblock.rs b/fs/erofs/rust/erofs_sys/superblock.rs
index fc6b3cb00b18..f60657eff3d6 100644
--- a/fs/erofs/rust/erofs_sys/superblock.rs
+++ b/fs/erofs/rust/erofs_sys/superblock.rs
@@ -5,6 +5,7 @@
 use alloc::boxed::Box;
 use core::mem::size_of;
 
+use super::data::raw_iters::*;
 use super::data::*;
 use super::devices::*;
 use super::inode::*;
@@ -274,6 +275,18 @@ fn map(&self, inode: &I, offset: Off) -> MapResult {
             _ => todo!(),
         }
     }
+
+    fn mapped_iter<'b, 'a: 'b>(
+        &'a self,
+        inode: &'b I,
+        offset: Off,
+    ) -> PosixResult<Box<dyn BufferMapIter<'a> + 'b>>;
+
+    fn continuous_iter<'a>(
+        &'a self,
+        offset: Off,
+        len: Off,
+    ) -> PosixResult<Box<dyn ContinuousBufferIter<'a> + 'a>>;
 }
 
 pub(crate) struct SuperblockInfo<I, C, T>
diff --git a/fs/erofs/rust/erofs_sys/superblock/mem.rs b/fs/erofs/rust/erofs_sys/superblock/mem.rs
index 12bf797bd1e3..5756dc08744c 100644
--- a/fs/erofs/rust/erofs_sys/superblock/mem.rs
+++ b/fs/erofs/rust/erofs_sys/superblock/mem.rs
@@ -1,6 +1,7 @@
 // Copyright 2024 Yiyang Wu
 // SPDX-License-Identifier: MIT or GPL-2.0-or-later
 
+use super::alloc_helper::*;
 use super::data::raw_iters::ref_iter::*;
 use super::*;
 
@@ -33,6 +34,27 @@ fn as_filesystem(&self) -> &dyn FileSystem<I> {
         self
     }
 
+    fn mapped_iter<'b, 'a: 'b>(
+        &'a self,
+        inode: &'b I,
+        offset: Off,
+    ) -> PosixResult<Box<dyn BufferMapIter<'a> + 'b>> {
+        heap_alloc(RefMapIter::new(
+            &self.sb,
+            &self.backend,
+            MapIter::new(self, inode, offset),
+        ))
+        .map(|v| v as Box<dyn BufferMapIter<'a> + 'b>)
+    }
+    fn continuous_iter<'a>(
+        &'a self,
+        offset: Off,
+        len: Off,
+    ) -> PosixResult<Box<dyn ContinuousBufferIter<'a> + 'a>> {
+        heap_alloc(ContinuousRefIter::new(&self.sb, &self.backend, offset, len))
+            .map(|v| v as Box<dyn ContinuousBufferIter<'a> + 'a>)
+    }
+
     fn device_info(&self) -> &DeviceInfo {
         &self.device_info
     }
-- 
2.46.0