linux-kernel - Re: [PATCH v5 2/4] rust: debugfs: Bind file creation for long-lived Display

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Message-ID: <168479280062ccf6e0dd45c77fea474fb1791ab2.camel@nvidia.com>
Date: Wed, 7 May 2025 19:41:25 +0000
From: Timur Tabi <ttabi@...dia.com>
To: "tmgross@...ch.edu" <tmgross@...ch.edu>, "benno.lossin@...ton.me"
	<benno.lossin@...ton.me>, "gregkh@...uxfoundation.org"
	<gregkh@...uxfoundation.org>, "gary@...yguo.net" <gary@...yguo.net>,
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CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v5 2/4] rust: debugfs: Bind file creation for long-lived
 Display

On Mon, 2025-05-05 at 23:51 +0000, Matthew Maurer wrote:

> +    /// Create a file in a DebugFS directory with the provided name, and contents from invoking
> +    /// [`Display::fmt`] on the provided reference.

Is there a typo in this sentence?  I can't quite parse it.

> +    pub fn display_file<'b, T: Display + Sized>(
> +        &'b self,
> +        name: &CStr,
> +        data: &'static T,
> +    ) -> File<'b> {
> +        // SAFETY:
> +        // * `name` is a NUL-terminated C string, living across the call, by `CStr` invariant.
> +        // * `parent` is a live `dentry` since we have a reference to it.
> +        // * `vtable` is all stock `seq_file` implementations except for `open`.
> +        //   `open`'s only requirement beyond what is provided to all open functions is that the
> +        //   inode's data pointer must point to a `T` that will outlive it, which we know because
> +        //   we have a static reference.
> +        #[cfg(CONFIG_DEBUG_FS)]
> +        let ptr = unsafe {
> +            bindings::debugfs_create_file_full(
> +                name.as_char_ptr(),
> +                0o444,

Can you make the mode a parameter?  I get that you're not supporting writing yet, but there should
be a choice as to whether it's 0o444, 0o440, or 0o400.

Also, maybe use S_IRUSR, S_IRGRP, and S_IROTH?