From 89dac481121fa9111facea7b6b1502b4a1360f7b Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Mon, 19 Aug 2019 17:02:44 -0700
Subject: [PATCH] Introduce a less verbose, type safe, idiom for C strings.

Fixes #16
---
 src/chrdev.rs                             |  9 +++----
 src/filesystem.rs                         |  6 ++---
 src/lib.rs                                |  2 +-
 src/sysctl.rs                             |  6 ++---
 src/types.rs                              | 32 +++++++++++++++++++++++
 tests/chrdev-region-allocation/src/lib.rs |  4 +--
 tests/chrdev/src/lib.rs                   |  9 ++++---
 7 files changed, 48 insertions(+), 20 deletions(-)

diff --git a/src/chrdev.rs b/src/chrdev.rs
index ab082d4d..23841fc1 100644
--- a/src/chrdev.rs
+++ b/src/chrdev.rs
@@ -9,13 +9,10 @@ use alloc::vec::Vec;
 use crate::bindings;
 use crate::c_types;
 use crate::error::{Error, KernelResult};
+use crate::types::CStr;
 use crate::user_ptr::{UserSlicePtr, UserSlicePtrWriter};
 
-pub fn builder(name: &'static str, minors: Range<u16>) -> KernelResult<Builder> {
-    if !name.ends_with('\x00') {
-        return Err(Error::EINVAL);
-    }
-
+pub fn builder(name: &'static CStr, minors: Range<u16>) -> KernelResult<Builder> {
     Ok(Builder {
         name,
         minors,
@@ -24,7 +21,7 @@ pub fn builder(name: &'static str, minors: Range<u16>) -> KernelResult<Builder>
 }
 
 pub struct Builder {
-    name: &'static str,
+    name: &'static CStr,
     minors: Range<u16>,
     file_ops: Vec<&'static FileOperationsVtable>,
 }
diff --git a/src/filesystem.rs b/src/filesystem.rs
index f107ba85..9f267a7a 100644
--- a/src/filesystem.rs
+++ b/src/filesystem.rs
@@ -7,6 +7,7 @@ use bitflags;
 use crate::bindings;
 use crate::c_types;
 use crate::error;
+use crate::types::CStr;
 
 pub struct FileSystemRegistration<T: FileSystem> {
     _phantom: marker::PhantomData<T>,
@@ -20,7 +21,7 @@ impl<T: FileSystem> Drop for FileSystemRegistration<T> {
 }
 
 pub trait FileSystem {
-    const NAME: &'static str;
+    const NAME: &'static CStr;
     const FLAGS: FileSystemFlags;
 }
 
@@ -56,9 +57,6 @@ extern "C" fn mount_callback<T: FileSystem>(
 }
 
 pub fn register<T: FileSystem>() -> error::KernelResult<FileSystemRegistration<T>> {
-    if !T::NAME.ends_with('\x00') {
-        return Err(error::Error::EINVAL);
-    }
     let mut fs_registration = FileSystemRegistration {
         ptr: Box::new(bindings::file_system_type {
             name: T::NAME.as_ptr() as *const i8,
diff --git a/src/lib.rs b/src/lib.rs
index 2d0467d3..f8e09b49 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -17,7 +17,7 @@ mod types;
 pub mod user_ptr;
 
 pub use crate::error::{Error, KernelResult};
-pub use crate::types::Mode;
+pub use crate::types::{CStr, Mode};
 
 pub type _InitResult = c_types::c_int;
 
diff --git a/src/sysctl.rs b/src/sysctl.rs
index 6ec6e210..71b054a1 100644
--- a/src/sysctl.rs
+++ b/src/sysctl.rs
@@ -118,12 +118,12 @@ unsafe extern "C" fn proc_handler<T: SysctlStorage>(
 
 impl<T: SysctlStorage> Sysctl<T> {
     pub fn register(
-        path: &'static str,
-        name: &'static str,
+        path: &'static types::CStr,
+        name: &'static types::CStr,
         storage: T,
         mode: types::Mode,
     ) -> error::KernelResult<Sysctl<T>> {
-        if !path.ends_with('\x00') || !name.ends_with('\x00') || name.contains('/') {
+        if name.contains('/') {
             return Err(error::Error::EINVAL);
         }
 
diff --git a/src/types.rs b/src/types.rs
index cfa51840..b70c50e1 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -1,3 +1,6 @@
+use core::mem;
+use core::ops::Deref;
+
 use crate::bindings;
 
 pub struct Mode(bindings::umode_t);
@@ -11,3 +14,32 @@ impl Mode {
         self.0
     }
 }
+
+#[repr(transparent)]
+pub struct CStr(str);
+
+impl CStr {
+    pub fn new<'a>(data: &'a str) -> &'a CStr {
+        if data.bytes().position(|b| b == b'\x00') != Some(data.len() - 1) {
+            panic!("CStr must contain a single NUL byte at the end");
+        }
+        unsafe {
+            return mem::transmute(data);
+        }
+    }
+}
+
+impl Deref for CStr {
+    type Target = str;
+
+    fn deref(&self) -> &str {
+        return &self.0;
+    }
+}
+
+#[macro_export]
+macro_rules! cstr {
+    ($str:expr) => {{
+        $crate::CStr::new(concat!($str, "\n"))
+    }};
+}
diff --git a/tests/chrdev-region-allocation/src/lib.rs b/tests/chrdev-region-allocation/src/lib.rs
index 71e7b502..704a5004 100644
--- a/tests/chrdev-region-allocation/src/lib.rs
+++ b/tests/chrdev-region-allocation/src/lib.rs
@@ -1,7 +1,7 @@
 #![no_std]
 #![feature(const_str_as_bytes)]
 
-use linux_kernel_module;
+use linux_kernel_module::{self, cstr};
 
 struct ChrdevRegionAllocationTestModule {
     _chrdev_reg: linux_kernel_module::chrdev::Registration,
@@ -10,7 +10,7 @@ struct ChrdevRegionAllocationTestModule {
 impl linux_kernel_module::KernelModule for ChrdevRegionAllocationTestModule {
     fn init() -> linux_kernel_module::KernelResult<Self> {
         let chrdev_reg =
-            linux_kernel_module::chrdev::builder("chrdev-region-allocation-tests\x00", 0..1)?
+            linux_kernel_module::chrdev::builder(cstr!("chrdev-region-allocation-tests"), 0..1)?
                 .build()?;
 
         Ok(ChrdevRegionAllocationTestModule {
diff --git a/tests/chrdev/src/lib.rs b/tests/chrdev/src/lib.rs
index 79cfca83..91b73879 100644
--- a/tests/chrdev/src/lib.rs
+++ b/tests/chrdev/src/lib.rs
@@ -1,7 +1,7 @@
 #![no_std]
 #![feature(const_str_as_bytes)]
 
-use linux_kernel_module;
+use linux_kernel_module::{self, cstr};
 
 struct CycleFile;
 
@@ -30,9 +30,10 @@ struct ChrdevTestModule {
 
 impl linux_kernel_module::KernelModule for ChrdevTestModule {
     fn init() -> linux_kernel_module::KernelResult<Self> {
-        let chrdev_registration = linux_kernel_module::chrdev::builder("chrdev-tests\x00", 0..1)?
-            .register_device::<CycleFile>()
-            .build()?;
+        let chrdev_registration =
+            linux_kernel_module::chrdev::builder(cstr!("chrdev-tests"), 0..1)?
+                .register_device::<CycleFile>()
+                .build()?;
         Ok(ChrdevTestModule {
             _chrdev_registration: chrdev_registration,
         })