[RFC PATCH 02/24] erofs: add superblock data structure in Rust

Yiyang Wu
2024-09-16T13:56:43Z

This patch adds a compilable super_rs.rs and introduces superblock
data structure in Rust. Note that this patch leaves C-side code
untouched.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
fs/erofs/Kconfig | 10 ++
fs/erofs/Makefile | 1 +
fs/erofs/rust/erofs_sys.rs | 22 +++++
fs/erofs/rust/erofs_sys/superblock.rs | 132 ++++++++++++++++++++++++++
fs/erofs/rust/mod.rs | 4 +
fs/erofs/super_rs.rs | 9 ++
6 files changed, 178 insertions(+)
create mode 100644 fs/erofs/rust/erofs_sys.rs
create mode 100644 fs/erofs/rust/erofs_sys/superblock.rs
create mode 100644 fs/erofs/rust/mod.rs
create mode 100644 fs/erofs/super_rs.rs

diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 6ea60661fa55..e2883efbf497 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -178,3 +178,13 @@ config EROFS_FS_PCPU_KTHREAD_HIPRI
at higher priority.

If unsure, say N.
+
+config EROFS_FS_RUST
+ bool "EROFS use RUST Replacement (EXPERIMENTAL)"
+ depends on EROFS_FS && RUST
+ help
+ This permits EROFS to use EXPERIMENTAL Rust implementation
+ for EROFS. This should be considered as an experimental
+ feature for now.
+
+ If unsure, say N.
diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
index 4331d53c7109..fb46a2c7fb50 100644
--- a/fs/erofs/Makefile
+++ b/fs/erofs/Makefile
@@ -9,3 +9,4 @@ erofs-$(CONFIG_EROFS_FS_ZIP_DEFLATE) += decompressor_deflate.o
erofs-$(CONFIG_EROFS_FS_ZIP_ZSTD) += decompressor_zstd.o
erofs-$(CONFIG_EROFS_FS_BACKED_BY_FILE) += fileio.o
erofs-$(CONFIG_EROFS_FS_ONDEMAND) += fscache.o
+erofs-$(CONFIG_EROFS_FS_RUST) += super_rs.o
diff --git a/fs/erofs/rust/erofs_sys.rs b/fs/erofs/rust/erofs_sys.rs
new file mode 100644
index 000000000000..0f1400175fc2
--- /dev/null
+++ b/fs/erofs/rust/erofs_sys.rs
@@ -0,0 +1,22 @@
+#![allow(dead_code)]
+// Copyright 2024 Yiyang Wu
+// SPDX-License-Identifier: MIT or GPL-2.0-or-later
+
+//! A pure Rust implementation of the EROFS filesystem.
+//! Technical Details are documented in the [EROFS Documentation](https://erofs.docs.kernel.org/en/latest/)
+
+// It's unavoidable to import alloc here. Since there are so many backends there and if we want to
+// to use trait object to export Filesystem pointer. The alloc crate here is necessary.
+
+#[cfg(not(CONFIG_EROFS_FS = "y"))]
+extern crate alloc;
+
+/// Erofs requires block index to a 32 bit unsigned integer.
+pub(crate) type Blk = u32;
+/// Erofs requires normal offset to be a 64bit unsigned integer.
+pub(crate) type Off = u64;
+/// Erofs requires inode nid to be a 64bit unsigned integer.
+pub(crate) type Nid = u64;
+/// Erofs Super Offset to read the ondisk superblock
+pub(crate) const EROFS_SUPER_OFFSET: Off = 1024;
+pub(crate) mod superblock;
diff --git a/fs/erofs/rust/erofs_sys/superblock.rs b/fs/erofs/rust/erofs_sys/superblock.rs
new file mode 100644
index 000000000000..213be6dbc553
--- /dev/null
+++ b/fs/erofs/rust/erofs_sys/superblock.rs
@@ -0,0 +1,132 @@
+// Copyright 2024 Yiyang Wu
+// SPDX-License-Identifier: MIT or GPL-2.0-or-later
+
+use super::*;
+use core::mem::size_of;
+
+/// The ondisk superblock structure.
+#[derive(Debug, Clone, Copy, Default)]
+#[repr(C)]
+pub(crate) struct SuperBlock {
+ pub(crate) magic: u32,
+ pub(crate) checksum: i32,
+ pub(crate) feature_compat: i32,
+ pub(crate) blkszbits: u8,
+ pub(crate) sb_extslots: u8,
+ pub(crate) root_nid: i16,
+ pub(crate) inos: i64,
+ pub(crate) build_time: i64,
+ pub(crate) build_time_nsec: i32,
+ pub(crate) blocks: i32,
+ pub(crate) meta_blkaddr: u32,
+ pub(crate) xattr_blkaddr: u32,
+ pub(crate) uuid: [u8; 16],
+ pub(crate) volume_name: [u8; 16],
+ pub(crate) feature_incompat: i32,
+ pub(crate) compression: i16,
+ pub(crate) extra_devices: i16,
+ pub(crate) devt_slotoff: i16,
+ pub(crate) dirblkbits: u8,
+ pub(crate) xattr_prefix_count: u8,
+ pub(crate) xattr_prefix_start: i32,
+ pub(crate) packed_nid: i64,
+ pub(crate) xattr_filter_reserved: u8,
+ pub(crate) reserved: [u8; 23],
+}
+
+impl TryFrom<&[u8]> for SuperBlock {
+ type Error = core::array::TryFromSliceError;
+ fn try_from(value: &[u8]) -> Result<Self, Self::Error> {
+ value[0..128].try_into()
+ }
+}
+
+impl From<[u8; 128]> for SuperBlock {
+ fn from(value: [u8; 128]) -> Self {
+ Self {
+ magic: u32::from_le_bytes([value[0], value[1], value[2], value[3]]),
+ checksum: i32::from_le_bytes([value[4], value[5], value[6], value[7]]),
+ feature_compat: i32::from_le_bytes([value[8], value[9], value[10], value[11]]),
+ blkszbits: value[12],
+ sb_extslots: value[13],
+ root_nid: i16::from_le_bytes([value[14], value[15]]),
+ inos: i64::from_le_bytes([
+ value[16], value[17], value[18], value[19], value[20], value[21], value[22],
+ value[23],
+ ]),
+ build_time: i64::from_le_bytes([
+ value[24], value[25], value[26], value[27], value[28], value[29], value[30],
+ value[31],
+ ]),
+ build_time_nsec: i32::from_le_bytes([value[32], value[33], value[34], value[35]]),
+ blocks: i32::from_le_bytes([value[36], value[37], value[38], value[39]]),
+ meta_blkaddr: u32::from_le_bytes([value[40], value[41], value[42], value[43]]),
+ xattr_blkaddr: u32::from_le_bytes([value[44], value[45], value[46], value[47]]),
+ uuid: value[48..64].try_into().unwrap(),
+ volume_name: value[64..80].try_into().unwrap(),
+ feature_incompat: i32::from_le_bytes([value[80], value[81], value[82], value[83]]),
+ compression: i16::from_le_bytes([value[84], value[85]]),
+ extra_devices: i16::from_le_bytes([value[86], value[87]]),
+ devt_slotoff: i16::from_le_bytes([value[88], value[89]]),
+ dirblkbits: value[90],
+ xattr_prefix_count: value[91],
+ xattr_prefix_start: i32::from_le_bytes([value[92], value[93], value[94], value[95]]),
+ packed_nid: i64::from_le_bytes([
+ value[96], value[97], value[98], value[99], value[100], value[101], value[102],
+ value[103],
+ ]),
+ xattr_filter_reserved: value[104],
+ reserved: value[105..128].try_into().unwrap(),
+ }
+ }
+}
+
+pub(crate) type SuperBlockBuf = [u8; size_of::<SuperBlock>()];
+pub(crate) const SUPERBLOCK_EMPTY_BUF: SuperBlockBuf = [0; size_of::<SuperBlock>()];
+
+/// Used for external address calculation.
+pub(crate) struct Accessor {
+ pub(crate) base: Off,
+ pub(crate) off: Off,
+ pub(crate) len: Off,
+ pub(crate) nr: Off,
+}
+
+impl Accessor {
+ pub(crate) fn new(address: Off, bits: Off) -> Self {
+ let sz = 1 << bits;
+ let mask = sz - 1;
+ Accessor {
+ base: (address >> bits) << bits,
+ off: address & mask,
+ len: sz - (address & mask),
+ nr: address >> bits,
+ }
+ }
+}
+
+impl SuperBlock {
+ pub(crate) fn blk_access(&self, address: Off) -> Accessor {
+ Accessor::new(address, self.blkszbits as Off)
+ }
+
+ pub(crate) fn blknr(&self, pos: Off) -> Blk {
+ (pos >> self.blkszbits) as Blk
+ }
+
+ pub(crate) fn blkpos(&self, blk: Blk) -> Off {
+ (blk as Off) << self.blkszbits
+ }
+
+ pub(crate) fn blksz(&self) -> Off {
+ 1 << self.blkszbits
+ }
+
+ pub(crate) fn blk_round_up(&self, addr: Off) -> Blk {
+ ((addr + self.blksz() - 1) >> self.blkszbits) as Blk
+ }
+
+ pub(crate) fn iloc(&self, nid: Nid) -> Off {
+ self.blkpos(self.meta_blkaddr) + ((nid as Off) << (5 as Off))
+ }
+}
diff --git a/fs/erofs/rust/mod.rs b/fs/erofs/rust/mod.rs
new file mode 100644
index 000000000000..e6c0731f2533
--- /dev/null
+++ b/fs/erofs/rust/mod.rs
@@ -0,0 +1,4 @@
+// Copyright 2024 Yiyang Wu
+// SPDX-License-Identifier: MIT or GPL-2.0-or-later
+
+pub(crate) mod erofs_sys;
diff --git a/fs/erofs/super_rs.rs b/fs/erofs/super_rs.rs
new file mode 100644
index 000000000000..4b8cbef507e3
--- /dev/null
+++ b/fs/erofs/super_rs.rs
@@ -0,0 +1,9 @@
+// Copyright 2024 Yiyang Wu
+// SPDX-License-Identifier: MIT or GPL-2.0-or-later
+
+//! EROFS Rust Kernel Module Helpers Implementation
+//! This is only for experimental purpose. Feedback is always welcome.
+
+#[allow(dead_code)]
+#[allow(missing_docs)]
+pub(crate) mod rust;
--
2.46.0