[RFC PATCH 10/24] erofs: add device_infos implementation in Rust

[Yiyang Wu via Linux-erofs <linux-erofs@lists.ozlabs.org>]

Add device_infos implementation in rust. It will later be used
to be put inside the SuperblockInfo. This mask and spec can later
be used to chunk-based image file block mapping.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
 fs/erofs/rust/erofs_sys/devices.rs | 47 ++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/fs/erofs/rust/erofs_sys/devices.rs b/fs/erofs/rust/erofs_sys/devices.rs
index 097676ee8720..7495164c7bd0 100644
--- a/fs/erofs/rust/erofs_sys/devices.rs
+++ b/fs/erofs/rust/erofs_sys/devices.rs
@@ -1,6 +1,10 @@
 // Copyright 2024 Yiyang Wu
 // SPDX-License-Identifier: MIT or GPL-2.0-or-later
 
+use super::alloc_helper::*;
+use super::data::raw_iters::*;
+use super::data::*;
+use super::*;
 use alloc::vec::Vec;
 
 /// Device specification.
@@ -21,8 +25,51 @@ pub(crate) struct DeviceSlot {
     reserved: [u8; 56],
 }
 
+impl From<[u8; 128]> for DeviceSlot {
+    fn from(data: [u8; 128]) -> Self {
+        Self {
+            tags: data[0..64].try_into().unwrap(),
+            blocks: u32::from_le_bytes([data[64], data[65], data[66], data[67]]),
+            mapped_blocks: u32::from_le_bytes([data[68], data[69], data[70], data[71]]),
+            reserved: data[72..128].try_into().unwrap(),
+        }
+    }
+}
+
 /// Device information.
 pub(crate) struct DeviceInfo {
     pub(crate) mask: u16,
     pub(crate) specs: Vec<DeviceSpec>,
 }
+
+pub(crate) fn get_device_infos<'a>(
+    iter: &mut (dyn ContinuousBufferIter<'a> + 'a),
+) -> PosixResult<DeviceInfo> {
+    let mut specs = Vec::new();
+    for data in iter {
+        let buffer = data?;
+        let mut cur: usize = 0;
+        let len = buffer.content().len();
+        while cur + 128 <= len {
+            let slot_data: [u8; 128] = buffer.content()[cur..cur + 128].try_into().unwrap();
+            let slot = DeviceSlot::from(slot_data);
+            cur += 128;
+            push_vec(
+                &mut specs,
+                DeviceSpec {
+                    tags: slot.tags,
+                    blocks: slot.blocks,
+                    mapped_blocks: slot.mapped_blocks,
+                },
+            )?;
+        }
+    }
+
+    let mask = if specs.is_empty() {
+        0
+    } else {
+        (1 << (specs.len().ilog2() + 1)) - 1
+    };
+
+    Ok(DeviceInfo { mask, specs })
+}
-- 
2.46.0