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Implement THIS_MODULE equivalent #15

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Implement THIS_MODULE equivalent #15

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Implement THIS_MODULE equivalent
ojeda Sep 18, 2020
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ojeda Oct 4, 2020
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5 changes: 2 additions & 3 deletions rust/kernel/src/chrdev.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@ impl Builder {
self
}

pub fn build(self) -> KernelResult<Registration> {
pub fn build(self, this_module: *mut bindings::module) -> KernelResult<Registration> {
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We need a safer wrapper around this, otherwise passing the raw ptr makes this interface unsafe.

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Passing the address is not unsafe on its own. I agree that it could look better (e.g. a struct ThisModule as I mentioned in the message above).

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Because this will deref the ptr, and creating a raw ptr is safe, the impact is that this is unsound :-)

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Yeah, it is definitely unsound, but the interface isn't unsafe due to the pointer passing on its own -- i.e. if we could check the pointer (somehow), then the function wouldn't need to be unsafe to be sound.

Related: at some point we will have to establish some guidelines in the docs (before Rust code starts growing quickly with people calling kernel APIs directly etc.) on "how much soundness-correct" we want to be (see similar discussions in e.g. cxx).

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Sure, but there's no way to check if the pointer is correct :-)

In general, safe interfaces can't really take raw pointers for this reason.

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I know, that is why I said "somehow" :-)

I think in my first reply you understood I was disagreeing about the function needing to be marked unsafe or having a proper abstraction -- I was only (pedantically) pointing out that it is not the passing but what we do with the pointer that makes the function unsafe.

let mut dev: bindings::dev_t = 0;
let res = unsafe {
bindings::alloc_chrdev_region(
Expand All @@ -58,8 +58,7 @@ impl Builder {
for (i, file_op) in self.file_ops.iter().enumerate() {
unsafe {
bindings::cdev_init(&mut cdevs[i], *file_op);
// TODO: proper `THIS_MODULE` handling
cdevs[i].owner = core::ptr::null_mut();
cdevs[i].owner = this_module;
let rc = bindings::cdev_add(&mut cdevs[i], dev + i as bindings::dev_t, 1);
if rc != 0 {
// Clean up the ones that were allocated.
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14 changes: 12 additions & 2 deletions rust/module/src/lib.rs
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Expand Up @@ -242,8 +242,7 @@ pub fn module(ts: TokenStream) -> TokenStream {
#[used]
static __{name}_{param_name}_struct: __{name}_{param_name}_RacyKernelParam = __{name}_{param_name}_RacyKernelParam(kernel::bindings::kernel_param {{
name: __{name}_{param_name}_name,
// TODO: `THIS_MODULE`
mod_: core::ptr::null_mut(),
mod_: THIS_MODULE.0,
ops: unsafe {{ &kernel::bindings::param_ops_{param_kernel_type} }} as *const kernel::bindings::kernel_param_ops,
perm: {permissions},
level: -1,
Expand All @@ -269,6 +268,17 @@ pub fn module(ts: TokenStream) -> TokenStream {
"
static mut __MOD: Option<{type_}> = None;

struct __THIS_MODULE(*mut kernel::bindings::module);

unsafe impl Sync for __THIS_MODULE {{
}}

#[cfg(MODULE)]
static THIS_MODULE: __THIS_MODULE = __THIS_MODULE(unsafe {{ &kernel::bindings::__this_module }} as *const _ as *mut kernel::bindings::module);

#[cfg(not(MODULE))]
static THIS_MODULE: __THIS_MODULE = __THIS_MODULE(core::ptr::null_mut());

// Loadable modules need to export the `{{init,cleanup}}_module` identifiers
#[cfg(MODULE)]
#[no_mangle]
Expand Down