[RFC PATCH 24/24] erofs: introduce xattrs replacement to C

Yiyang Wu
2024-09-16T13:57:26Z

This patch introduces erofs_getxattr_rust and erofs_listxattr_rust to C
and can replace the original xattr logic entirely.

Note that the original acl implementation is tweaked with a lifted
function called erofs_getxattr_nobuf, so that difference of the calling
convention of Rust side code can be bridged.

Signed-off-by: Yiyang Wu <toolmanp@tlmp.cc>
---
fs/erofs/Makefile | 3 ++
fs/erofs/rust_bindings.h | 8 +++
fs/erofs/xattr.c | 31 +++++++++---
fs/erofs/xattr.h | 7 +++
fs/erofs/xattr_rs.rs | 106 +++++++++++++++++++++++++++++++++++++++
5 files changed, 148 insertions(+), 7 deletions(-)
create mode 100644 fs/erofs/xattr_rs.rs

diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
index 219ddca0642e..ad0650698f4b 100644
--- a/fs/erofs/Makefile
+++ b/fs/erofs/Makefile
@@ -10,3 +10,6 @@ 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 namei_rs.o dir_rs.o data_rs.o rust_helpers.o
+ifeq ($(CONFIG_EROFS_FS_XATTR),y)
+erofs-$(CONFIG_EROFS_FS_RUST) += xattr_rs.o
+endif
diff --git a/fs/erofs/rust_bindings.h b/fs/erofs/rust_bindings.h
index ad9aa75a7a2c..e5a879efd9e2 100644
--- a/fs/erofs/rust_bindings.h
+++ b/fs/erofs/rust_bindings.h
@@ -28,4 +28,12 @@ extern int erofs_readdir_rust(struct file *file, struct dir_context *ctx);
struct erofs_map_blocks;
extern int erofs_map_blocks_rust(struct inode *inode,
struct erofs_map_blocks *map);
+extern int erofs_getxattr_rust(struct inode *inode, unsigned int flags,
+ const char *name, void *buffer, size_t size);
+extern ssize_t erofs_listxattr_rust(struct dentry *dentry, char *buffer,
+ size_t buffer_size);
+#ifdef CONFIG_EROFS_FS_POSIX_ACL
+extern int erofs_getxattr_nobuf_rust(struct inode *inode, int prefix,
+ const char *name, char **value);
+#endif
#endif
diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
index a90d7d649739..0296c5809695 100644
--- a/fs/erofs/xattr.c
+++ b/fs/erofs/xattr.c
@@ -8,6 +8,7 @@
#include <linux/xxhash.h>
#include "xattr.h"

+#ifndef CONFIG_EROFS_FS_RUST
struct erofs_xattr_iter {
struct super_block *sb;
struct erofs_buf buf;
@@ -122,6 +123,7 @@ static int erofs_init_inode_xattrs(struct inode *inode)
clear_and_wake_up_bit(EROFS_I_BL_XATTR_BIT, &vi->flags);
return ret;
}
+#endif

static bool erofs_xattr_user_list(struct dentry *dentry)
{
@@ -175,6 +177,7 @@ const struct xattr_handler * const erofs_xattr_handlers[] = {
NULL,
};

+#ifndef CONFIG_EROFS_FS_RUST
static int erofs_xattr_copy_to_buffer(struct erofs_xattr_iter *it,
unsigned int len)
{
@@ -509,8 +512,28 @@ int erofs_xattr_prefixes_init(struct super_block *sb)
erofs_xattr_prefixes_cleanup(sb);
return ret;
}
+#endif

#ifdef CONFIG_EROFS_FS_POSIX_ACL
+#ifndef CONFIG_EROFS_FS_RUST
+static int erofs_getxattr_nobuf(struct inode *inode, int prefix,
+ const char *name, char **value)
+{
+ int rc;
+ char *buf = NULL;
+ rc = erofs_getxattr(inode, prefix, name, NULL, 0);
+ if (rc > 0) {
+ buf = kmalloc(rc, GFP_KERNEL);
+ if (!value)
+ return ENOMEM;
+ rc = erofs_getxattr(inode, prefix, name, buf, rc);
+ }
+ *value = buf;
+ return rc;
+}
+#else
+#define erofs_getxattr_nobuf erofs_getxattr_nobuf_rust
+#endif
struct posix_acl *erofs_get_acl(struct inode *inode, int type, bool rcu)
{
struct posix_acl *acl;
@@ -531,13 +554,7 @@ struct posix_acl *erofs_get_acl(struct inode *inode, int type, bool rcu)
return ERR_PTR(-EINVAL);
}

- rc = erofs_getxattr(inode, prefix, "", NULL, 0);
- if (rc > 0) {
- value = kmalloc(rc, GFP_KERNEL);
- if (!value)
- return ERR_PTR(-ENOMEM);
- rc = erofs_getxattr(inode, prefix, "", value, rc);
- }
+ rc = erofs_getxattr_nobuf(inode, prefix, "", &value);

if (rc == -ENOATTR)
acl = NULL;
diff --git a/fs/erofs/xattr.h b/fs/erofs/xattr.h
index b246cd0e135e..2b934c25e991 100644
--- a/fs/erofs/xattr.h
+++ b/fs/erofs/xattr.h
@@ -46,10 +46,17 @@ static inline const char *erofs_xattr_prefix(unsigned int idx,

extern const struct xattr_handler * const erofs_xattr_handlers[];

+#ifdef CONFIG_EROFS_FS_RUST
+#define erofs_getxattr erofs_getxattr_rust
+#define erofs_listxattr erofs_listxattr_rust
+static inline int erofs_xattr_prefixes_init(struct super_block *sb) { return 0; }
+static inline void erofs_xattr_prefixes_cleanup(struct super_block *sb) {}
+#else
int erofs_xattr_prefixes_init(struct super_block *sb);
void erofs_xattr_prefixes_cleanup(struct super_block *sb);
int erofs_getxattr(struct inode *, int, const char *, void *, size_t);
ssize_t erofs_listxattr(struct dentry *, char *, size_t);
+#endif
#else
static inline int erofs_xattr_prefixes_init(struct super_block *sb) { return 0; }
static inline void erofs_xattr_prefixes_cleanup(struct super_block *sb) {}
diff --git a/fs/erofs/xattr_rs.rs b/fs/erofs/xattr_rs.rs
new file mode 100644
index 000000000000..9429507089f6
--- /dev/null
+++ b/fs/erofs/xattr_rs.rs
@@ -0,0 +1,106 @@
+// 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::{dentry, inode};
+use kernel::container_of;
+
+use rust::{erofs_sys::xattrs::*, kinode::*, ksuperblock::*};
+
+/// Used as a replacement for erofs_getattr.
+#[no_mangle]
+pub unsafe extern "C" fn erofs_getxattr_rust(
+ k_inode: NonNull<inode>,
+ index: c_uint,
+ name: NonNull<u8>,
+ buffer: NonNull<u8>,
+ size: usize,
+) -> c_int {
+ // SAFETY: super_block and superblockinfo is always initialized in k_inode.
+ let sbi = erofs_sbi(unsafe { NonNull::new(k_inode.as_ref().i_sb).unwrap() });
+ // 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: buffer is always initialized in the caller and name is null terminated C string.
+ unsafe {
+ match sbi.filesystem.get_xattr(
+ erofs_inode,
+ index,
+ core::ffi::CStr::from_ptr(name.as_ptr().cast()).to_bytes(),
+ &mut Some(core::slice::from_raw_parts_mut(
+ buffer.as_ptr().cast(),
+ size,
+ )),
+ ) {
+ Ok(value) => match value {
+ XAttrValue::Buffer(x) => x as c_int,
+ _ => unreachable!(),
+ },
+ Err(e) => i32::from(e) as c_int,
+ }
+ }
+}
+
+/// Used as a replacement for erofs_getattr_nobuf.
+#[no_mangle]
+pub unsafe extern "C" fn erofs_getxattr_nobuf_rust(
+ k_inode: NonNull<inode>,
+ index: u32,
+ name: NonNull<u8>,
+ mut value: NonNull<*mut u8>,
+) -> c_int {
+ // SAFETY: super_block and superblockinfo is always initialized in k_inode.
+ let sbi = erofs_sbi(unsafe { NonNull::new(k_inode.as_ref().i_sb).unwrap() });
+ // 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: buffer is always initialized in the caller and name is null terminated C string.
+ unsafe {
+ match sbi.filesystem.get_xattr(
+ erofs_inode,
+ index,
+ core::ffi::CStr::from_ptr(name.as_ptr().cast()).to_bytes(),
+ &mut None,
+ ) {
+ Ok(xattr_value) => match xattr_value {
+ XAttrValue::Vec(v) => {
+ let rc = v.len() as c_int;
+ *value.as_mut() = v.leak().as_mut_ptr().cast();
+ rc
+ }
+
+ _ => unreachable!(),
+ },
+ Err(e) => i32::from(e) as c_int,
+ }
+ }
+}
+
+/// Used as a replacement for erofs_getattr.
+#[no_mangle]
+pub unsafe extern "C" fn erofs_listxattr_rust(
+ dentry: NonNull<dentry>,
+ buffer: NonNull<u8>,
+ size: usize,
+) -> c_long {
+ // SAFETY: dentry is always initialized in the caller.
+ let k_inode = unsafe { dentry.as_ref().d_inode };
+ // SAFETY: We are sure that the inode is a Kernel Inode since alloc_inode is called.
+ let erofs_inode = unsafe { &*container_of!(k_inode, 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).i_sb).unwrap() });
+ match sbi.filesystem.list_xattrs(
+ erofs_inode,
+ // SAFETY: buffer is always initialized in the caller.
+ unsafe { core::slice::from_raw_parts_mut(buffer.as_ptr().cast(), size) },
+ ) {
+ Ok(value) => value as c_long,
+ Err(e) => i32::from(e) as c_long,
+ }
+}
--
2.46.0