linux-kernel - Re: [PATCH v2 2/2] rust: miscdevice: add base miscdevice abstraction

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Message-ID: <CAH5fLgjm=u_im776f9cTrqjKCYQ31F4t=_Dg6mDzCoSEGoJm-w@mail.gmail.com>
Date: Wed, 2 Oct 2024 16:24:58 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Miguel Ojeda <ojeda@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] rust: miscdevice: add base miscdevice abstraction

On Wed, Oct 2, 2024 at 4:06 PM Christian Brauner <brauner@...nel.org> wrote:
>
> On Tue, Oct 01, 2024 at 08:22:22AM GMT, Alice Ryhl wrote:
> > +unsafe extern "C" fn fops_open<T: MiscDevice>(
> > +    inode: *mut bindings::inode,
> > +    file: *mut bindings::file,
> > +) -> c_int {
> > +    // SAFETY: The pointers are valid and for a file being opened.
> > +    let ret = unsafe { bindings::generic_file_open(inode, file) };
> > +    if ret != 0 {
> > +        return ret;
> > +    }
>
> Do you have code where that function is used? Because this looks wrong
> or at least I don't understand from just a glance whether that
> generic_file_open() call makes sense.
>
> Illustrating how we get from opening /dev/binder to this call would
> help.

Hmm. I wrote this by comparing with the ashmem open callback. Now that
you mention it you are right that Binder does not call
generic_file_open ... I have to admit that I don't know what
generic_file_open does.

Alice