linux-kernel - Re: [PATCH v13 1/3] rust: io: add resource abstraction

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Message-Id: <D9C5D4EC-FA24-47DB-BE89-609713F093FF@collabora.com>
Date: Wed, 16 Jul 2025 13:52:36 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org,
 Fiona Behrens <me@...enk.dev>
Subject: Re: [PATCH v13 1/3] rust: io: add resource abstraction

Hi Alice,

> 
>> +        let inner = self.0.get();
>> +        // SAFETY: safe as per the invariants of `Resource`.
>> +        unsafe { (*inner).start }
>> +    }
>> +
>> +    /// Returns the name of the resource.
>> +    pub fn name(&self) -> &'static CStr {
>> +        let inner = self.0.get();
>> +        // SAFETY: safe as per the invariants of `Resource`
>> +        unsafe { CStr::from_char_ptr((*inner).name) }
> 
> This is 'static? I would like this safety comment to explicitly say that
> the string always lives forever no matter what resource you call this
> on.
> 
> Alice
> 

Actually, we have a bit of a problem here.

First, there appears to be no guarantee that a `Resource` has a valid name.

In fact:

#define DEFINE_RES_NAMED(_start, _size, _name, _flags) \
DEFINE_RES_NAMED_DESC(_start, _size, _name, _flags, IORES_DESC_NONE)
#define DEFINE_RES(_start, _size, _flags) \
DEFINE_RES_NAMED(_start, _size, NULL, _flags)

#define DEFINE_RES_IO_NAMED(_start, _size, _name) \
DEFINE_RES_NAMED((_start), (_size), (_name), IORESOURCE_IO)
#define DEFINE_RES_IO(_start, _size) \
DEFINE_RES_IO_NAMED((_start), (_size), NULL)

The non _NAMED version of these macros will assign a NULL pointer, so we can't
derive a CStr from that at all.

On top of that, although some call sites do use static names, i.e.:

struct resource ioport_resource = {
.name = "PCI IO",
.start = 0,
.end = IO_SPACE_LIMIT,
.flags = IORESOURCE_IO,
};
EXPORT_SYMBOL(ioport_resource);

struct resource iomem_resource = {
.name = "PCI mem",
.start = 0,
.end = -1,
.flags = IORESOURCE_MEM,
};
EXPORT_SYMBOL(iomem_resource);

static struct resource busn_resource = {
.name = "PCI busn",
.start = 0,
.end = 255,
.flags = IORESOURCE_BUS,
};

Some appear to use other, smaller lifetimes, like the one below:

struct pnp_resource *pnp_add_resource(struct pnp_dev *dev,
      struct resource *res)
{
struct pnp_resource *pnp_res;

pnp_res = pnp_new_resource(dev);
if (!pnp_res) {
dev_err(&dev->dev, "can't add resource %pR\n", res);
return NULL;
}

pnp_res->res = *res;
pnp_res->res.name = dev->name;

I guess the easiest solution is to drop 'static in order to account for the
above, and change the signature to return Option<&CStr> instead.  

We can also change Region to own the name, and pass name by value here:

    pub fn request_region(
        &self,
        start: ResourceSize,
        size: ResourceSize,
        name: &'static CStr <------

Thoughts?

— Daniel