ch04: remove proc entry when unloading the module

/ # insmod share/rust_proc.ko
[    7.874918] rust_proc: module verification failed: signature and/or required key missing - tainting kernel
[    7.876615] rust_proc: rust_proc is loaded
[    7.877263] rust_proc: succeeded to create a proc entry: 0xffff888005469300
/ # ls proc/
1              27             7              iomem          pressure
10             28             8              ioports        rust_demo
11             29             9              irq            schedstat
111            3              bootconfig     kallsyms       self
12             30             buddyinfo      kcore          slabinfo
120            31             bus            key-users      softirqs
13             32             cgroups        keys           stat
14             33             cmdline        kmsg           swaps
15             34             consoles       kpagecgroup    sys
16             35             cpuinfo        kpagecount     sysrq-trigger
17             36             crypto         kpageflags     sysvipc
18             38             devices        loadavg        thread-self
19             4              diskstats      locks          timer_list
2              40             dma            meminfo        tty
20             41             driver         misc           uptime
21             42             dynamic_debug  modules        version
22             5              execdomains    mounts         vmallocinfo
23             53             fb             mtrr           vmstat
24             6              filesystems    net            zoneinfo
25             61             fs             pagetypeinfo
26             62             interrupts     partitions
/ # ls proc/rust_demo/
rust_proc_fs
/ # rmmod rust_proc
[   14.860586] rust_proc: rust_proc is unloaded
/ # ls proc/rust_demo/
ls: proc/rust_demo/: No such file or directory

Author: Gioh Kim

rust/bindings/bindings_helper.h

@@ -37,6 +37,7 @@
 #include <linux/uaccess.h>
 #include <linux/uio.h>
 #include <linux/proc_fs.h>
+#include <linux/seq_file.h>
 
 /* `bindgen` gets confused at certain things. */
 const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;

samples/rust/rust_proc.rs

@@ -25,23 +25,49 @@ module! {
     license: "GPL",
 }
 
-struct RustProc {}
+struct RustProc {
+    parent: *mut bindings::proc_dir_entry,
+    _entry: *mut bindings::proc_dir_entry,
+}
 
 impl RustProc {
     unsafe extern "C" fn proc_open(
         _inode: *mut bindings::inode,
         _file: *mut bindings::file,
     ) -> i32 {
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+        pr_info!("proc_open is invoked\n");
+
+        unsafe {
+            let ret = bindings::single_open(_file, Some(Self::proc_show), ptr::null_mut());
+        }
         0 as i32
     }
 
-    unsafe extern "C" fn proc_read(
-        _file: *mut bindings::file,
-        _buf: *mut core::ffi::c_char,
-        _len: usize,
-        _off: *mut bindings::loff_t,
-    ) -> isize {
-        0 as isize
+    unsafe extern "C" fn proc_show(_m: *mut bindings::seq_file, _v: *mut core::ffi::c_void) -> i32 {
+        pr_info!("proc_read is invoked\n");
+        0 as i32
     }
 }
 
@@ -58,29 +84,43 @@ impl kernel::Module for RustProc {
                 proc_get_unmapped_area: None, // mandatory to prevent build error
                 proc_read_iter: None,         // mandatory to prevent build error
                 proc_open: Some(Self::proc_open),
-                proc_read: Some(Self::proc_read),
+                proc_read: None,
                 proc_write: None,
                 proc_lseek: None,
                 proc_release: None,
                 proc_poll: None,
                 proc_ioctl: None,
                 proc_mmap: None,
             };
+            let entry_name = CString::try_from_fmt(fmt!("{}", PROC_FS_NAME))?;
+            let entry: *mut bindings::proc_dir_entry =
+                bindings::proc_create(entry_name.as_char_ptr(), 0o644, parent, &proc_ops);
+            // How to check entry?
+            if entry.is_null() {
+                pr_info!("failed to create a proc entry\n");
+            } else {
+                pr_info!("succeeded to create a proc entry: {:p}\n", entry);
+            }
 
-            bindings::proc_create(
-                CString::try_from_fmt(fmt!("{}", PROC_FS_NAME))?.as_char_ptr(),
-                0o644,
+            Ok(RustProc {
                 parent,
-                &proc_ops,
-            );
+                _entry: entry,
+            })
         }
-
-        Ok(RustProc {})
     }
 }
 
 impl Drop for RustProc {
     fn drop(&mut self) {
+        unsafe {
+            let entry_name = CString::try_from_fmt(fmt!("{}", PROC_FS_NAME)).unwrap();
+            bindings::remove_proc_entry(entry_name.as_char_ptr(), self.parent);
+
+            let dir_name = CString::try_from_fmt(fmt!("{}", SUB_DIR_NAME)).unwrap();
+            bindings::remove_proc_entry(dir_name.as_char_ptr(), ptr::null_mut());
+        }
         pr_info!("rust_proc is unloaded\n");
     }
 }
+
+unsafe impl Sync for RustProc {}