[RFC PATCH 19/24] erofs: introduce namei alternative to C

Yiyang Wu
2024-09-16T13:57:16Z

This patch introduces erofs_lookup_rust and erofs_get_parent_rust
written in Rust as an alternative to the original namei.c.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
fs/erofs/Makefile | 2 +-
fs/erofs/internal.h | 2 ++
fs/erofs/namei.c | 2 ++
fs/erofs/namei_rs.rs | 56 ++++++++++++++++++++++++++++++++++++++++
fs/erofs/rust_bindings.h | 4 ++-
fs/erofs/super.c | 2 ++
6 files changed, 66 insertions(+), 2 deletions(-)
create mode 100644 fs/erofs/namei_rs.rs

diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
index 46de6f490ca2..0f748f3e0ff6 100644
--- a/fs/erofs/Makefile
+++ b/fs/erofs/Makefile
@@ -9,4 +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-$(CONFIG_EROFS_FS_RUST) += super_rs.o inode_rs.o rust_helpers.o
+erofs-$(CONFIG_EROFS_FS_RUST) += super_rs.o inode_rs.o namei_rs.o rust_helpers.o
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 42ce84783be7..1d9dfae285d5 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -442,6 +442,8 @@ int erofs_iget5_eq(struct inode *inode, void *opaque);
int erofs_iget5_set(struct inode *inode, void *opaque);
#ifdef CONFIG_EROFS_FS_RUST
#define erofs_iget erofs_iget_rust
+#define erofs_get_parent erofs_get_parent_rust
+#define erofs_lookup erofs_lookup_rust
#else
struct inode *erofs_iget(struct super_block *sb, erofs_nid_t nid);
#endif
diff --git a/fs/erofs/namei.c b/fs/erofs/namei.c
index c94d0c1608a8..f657d475c4a1 100644
--- a/fs/erofs/namei.c
+++ b/fs/erofs/namei.c
@@ -7,6 +7,7 @@
#include "xattr.h"
#include <trace/events/erofs.h>

+#ifndef CONFIG_EROFS_FS_RUST
struct erofs_qstr {
const unsigned char *name;
const unsigned char *end;
@@ -214,6 +215,7 @@ static struct dentry *erofs_lookup(struct inode *dir, struct dentry *dentry,
inode = erofs_iget(dir->i_sb, nid);
return d_splice_alias(inode, dentry);
}
+#endif

const struct inode_operations erofs_dir_iops = {
.lookup = erofs_lookup,
diff --git a/fs/erofs/namei_rs.rs b/fs/erofs/namei_rs.rs
new file mode 100644
index 000000000000..d73a0a7bee1e
--- /dev/null
+++ b/fs/erofs/namei_rs.rs
@@ -0,0 +1,56 @@
+// 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;
+use core::ffi::*;
+use core::ptr::NonNull;
+
+use kernel::bindings::{d_obtain_alias, d_splice_alias, dentry, inode};
+use kernel::container_of;
+
+use rust::{erofs_sys::operations::*, kinode::*, ksuperblock::*};
+
+/// Lookup function for dentry-inode lookup replacement.
+#[no_mangle]
+pub unsafe extern "C" fn erofs_lookup_rust(
+ k_inode: NonNull<inode>,
+ dentry: NonNull<dentry>,
+ _flags: c_uint,
+) -> *mut c_void {
+ // SAFETY: We are sure that the inode is a Kernel Inode since alloc_inode is called
+ let erofs_inode = unsafe { &*container_of!(k_inode.as_ptr(), KernelInode, k_inode) };
+ // SAFETY: The super_block is initialized when the erofs_alloc_sbi_rust is called.
+ let sbi = erofs_sbi(unsafe { NonNull::new(k_inode.as_ref().i_sb).unwrap() });
+ // SAFETY: this is backed by qstr which is c representation of a valid slice.
+ let name = unsafe {
+ core::str::from_utf8_unchecked(core::slice::from_raw_parts(
+ dentry.as_ref().d_name.name,
+ dentry.as_ref().d_name.__bindgen_anon_1.__bindgen_anon_1.len as usize,
+ ))
+ };
+ let k_inode: *mut inode =
+ dir_lookup(sbi.filesystem.as_ref(), &mut sbi.inodes, erofs_inode, name)
+ .map_or(core::ptr::null_mut(), |result| result.k_inode.as_mut_ptr());
+
+ // SAFETY: We are sure that the inner k_inode has already been initialized.
+ unsafe { d_splice_alias(k_inode, dentry.as_ptr()).cast() }
+}
+
+/// Exported as a replacement of erofs_get_parent.
+#[no_mangle]
+pub unsafe extern "C" fn erofs_get_parent_rust(child: NonNull<dentry>) -> *mut c_void {
+ // SAFETY: We are sure that the inode is a Kernel Inode since alloc_inode is called
+ let k_inode = unsafe { child.as_ref().d_inode };
+ // SAFETY: The super_block is initialized when the erofs_alloc_sbi_rust is called.
+ let sbi = erofs_sbi(unsafe { NonNull::new((*k_inode).i_sb).unwrap() }); // SAFETY: We are sure that the inode is a Kernel Inode since alloc_inode is called
+ let inode = unsafe { &*container_of!(k_inode, KernelInode, k_inode) };
+ let k_inode: *mut inode = dir_lookup(sbi.filesystem.as_ref(), &mut sbi.inodes, inode, "..")
+ .map_or(core::ptr::null_mut(), |result| result.k_inode.as_mut_ptr());
+ // SAFETY: We are sure that the inner k_inode has already been initialized
+ unsafe { d_obtain_alias(k_inode).cast() }
+}
diff --git a/fs/erofs/rust_bindings.h b/fs/erofs/rust_bindings.h
index 657f109dd6e7..b35014aa5cae 100644
--- a/fs/erofs/rust_bindings.h
+++ b/fs/erofs/rust_bindings.h
@@ -6,7 +6,6 @@

#include <linux/fs.h>

-
typedef u64 erofs_nid_t;
typedef u64 erofs_off_t;
/* data type for filesystem-wide blocks number */
@@ -21,4 +20,7 @@ extern void *erofs_alloc_sbi_rust(struct super_block *sb);
extern void *erofs_free_sbi_rust(struct super_block *sb);
extern int erofs_iget5_eq_rust(struct inode *inode, void *opaque);
extern struct inode *erofs_iget_rust(struct super_block *sb, erofs_nid_t nid);
+extern struct dentry *erofs_lookup_rust(struct inode *inode, struct dentry *dentry,
+ unsigned int flags);
+extern struct dentry *erofs_get_parent_rust(struct dentry *dentry);
#endif
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 659502bdf5fe..d49c804acf3d 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -554,6 +554,7 @@ static struct dentry *erofs_fh_to_parent(struct super_block *sb,
erofs_nfs_get_inode);
}

+#ifndef CONFIG_EROFS_FS_RUST
static struct dentry *erofs_get_parent(struct dentry *child)
{
erofs_nid_t nid;
@@ -565,6 +566,7 @@ static struct dentry *erofs_get_parent(struct dentry *child)
return ERR_PTR(err);
return d_obtain_alias(erofs_iget(child->d_sb, nid));
}
+#endif

static const struct export_operations erofs_export_ops = {
.encode_fh = generic_encode_ino32_fh,
--
2.46.0