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Date: Thu, 23 Oct 2025 12:09:54 +0200
Message-Id: <DDPMBR9EUYJ6.23AYG1B27BUEN@kernel.org>
Subject: Re: [PATCH v3 06/10] rust: debugfs: support for binary large
 objects
Cc: <gregkh@linuxfoundation.org>, <rafael@kernel.org>, <ojeda@kernel.org>,
 <alex.gaynor@gmail.com>, <boqun.feng@gmail.com>, <gary@garyguo.net>,
 <bjorn3_gh@protonmail.com>, <lossin@kernel.org>, <a.hindborg@kernel.org>,
 <tmgross@umich.edu>, <mmaurer@google.com>,
 <rust-for-linux@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
To: "Alice Ryhl" <aliceryhl@google.com>
From: "Danilo Krummrich" <dakr@kernel.org>
References: <20251022143158.64475-1-dakr@kernel.org>
 <20251022143158.64475-7-dakr@kernel.org> <aPnmriUUdbsQAu3e@google.com>
In-Reply-To: <aPnmriUUdbsQAu3e@google.com>

On Thu Oct 23, 2025 at 10:26 AM CEST, Alice Ryhl wrote:
> On Wed, Oct 22, 2025 at 04:30:40PM +0200, Danilo Krummrich wrote:
>> Introduce support for read-only, write-only, and read-write binary files
>> in Rust debugfs. This adds:
>>=20
>> - BinaryWriter and BinaryReader traits for writing to and reading from
>>   user slices in binary form.
>> - New Dir methods: read_binary_file(), write_binary_file(),
>>   `read_write_binary_file`.
>> - Corresponding FileOps implementations: BinaryReadFile,
>>   BinaryWriteFile, BinaryReadWriteFile.
>>=20
>> This allows kernel modules to expose arbitrary binary data through
>> debugfs, with proper support for offsets and partial reads/writes.
>>=20
>> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Reviewed-by: Matthew Maurer <mmaurer@google.com>
>> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
>
>> +extern "C" fn blob_read<T: BinaryWriter>(
>> +    file: *mut bindings::file,
>> +    buf: *mut c_char,
>> +    count: usize,
>> +    ppos: *mut bindings::loff_t,
>> +) -> isize {
>> +    // SAFETY:
>> +    // - `file` is a valid pointer to a `struct file`.
>> +    // - The type invariant of `FileOps` guarantees that `private_data`=
 points to a valid `T`.
>> +    let this =3D unsafe { &*((*file).private_data.cast::<T>()) };
>> +
>> +    // SAFETY:
>> +    // `ppos` is a valid `file::Offset` pointer.
>> +    // We have exclusive access to `ppos`.
>> +    let pos =3D unsafe { file::Offset::from_raw(ppos) };
>> +
>> +    let mut writer =3D UserSlice::new(UserPtr::from_ptr(buf.cast()), co=
unt).writer();
>> +
>> +    let ret =3D || -> Result<isize> {
>> +        let written =3D this.write_to_slice(&mut writer, pos)?;
>> +
>> +        Ok(written.try_into()?)
>
> Hmm ... a conversion? Sounds like write_to_slice() has the wrong return
> type.

write_to_slice() returns the number of bytes written as usize, which seems
correct, no?