Commit f8c78198 authored by Alice Ryhl's avatar Alice Ryhl Committed by Andrew Morton
Browse files

rust: miscdevice: add mmap support 

Add the ability to write a file_operations->mmap hook in Rust when using
the miscdevice abstraction.  The `vma` argument to the `mmap` hook uses
the `VmaNew` type from the previous commit; this type provides the correct
set of operations for a file_operations->mmap hook.

Link: https://lkml.kernel.org/r/20250408-vma-v16-7-d8b446e885d9@google.com


Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: default avatarLiam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: default avatarAndreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Cc: Alex Gaynor <alex.gaynor@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Benno Lossin <benno.lossin@proton.me>
Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Trevor Gross <tmgross@umich.edu>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent dcb81aea

rust/kernel/miscdevice.rs

+45 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
    error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},

    ffi::{c_int, c_long, c_uint, c_ulong},

    fs::File,

    mm::virt::VmaNew,

    prelude::*,

    seq_file::SeqFile,

    str::CStr,
@@ -119,6 +120,22 @@ fn release(device: Self::Ptr, _file: &File) { 
        drop(device);

    }



    /// Handle for mmap.

    ///

    /// This function is invoked when a user space process invokes the `mmap` system call on

    /// `file`. The function is a callback that is part of the VMA initializer. The kernel will do

    /// initial setup of the VMA before calling this function. The function can then interact with

    /// the VMA initialization by calling methods of `vma`. If the function does not return an

    /// error, the kernel will complete initialization of the VMA according to the properties of

    /// `vma`.

    fn mmap(

        _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,

        _file: &File,

        _vma: &VmaNew,

    ) -> Result {

        build_error!(VTABLE_DEFAULT_ERROR)

    }



    /// Handler for ioctls.

    ///

    /// The `cmd` argument is usually manipulated using the utilties in [`kernel::ioctl`].
@@ -223,6 +240,33 @@ impl<T: MiscDevice> MiscdeviceVTable<T> { 
        0

    }



    /// # Safety

    ///

    /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.

    /// `vma` must be a vma that is currently being mmap'ed with this file.

    unsafe extern "C" fn mmap(

        file: *mut bindings::file,

        vma: *mut bindings::vm_area_struct,

    ) -> c_int {

        // SAFETY: The mmap call of a file can access the private data.

        let private = unsafe { (*file).private_data };

        // SAFETY: This is a Rust Miscdevice, so we call `into_foreign` in `open` and

        // `from_foreign` in `release`, and `fops_mmap` is guaranteed to be called between those

        // two operations.

        let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };

        // SAFETY: The caller provides a vma that is undergoing initial VMA setup.

        let area = unsafe { VmaNew::from_raw(vma) };

        // SAFETY:

        // * The file is valid for the duration of this call.

        // * There is no active fdget_pos region on the file on this thread.

        let file = unsafe { File::from_raw_file(file) };



        match T::mmap(device, file, area) {

            Ok(()) => 0,

            Err(err) => err.to_errno(),

        }

    }



    /// # Safety

    ///

    /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
@@ -291,6 +335,7 @@ impl<T: MiscDevice> MiscdeviceVTable<T> { 
    const VTABLE: bindings::file_operations = bindings::file_operations {

        open: Some(Self::open),

        release: Some(Self::release),

        mmap: if T::HAS_MMAP { Some(Self::mmap) } else { None },

        unlocked_ioctl: if T::HAS_IOCTL {

            Some(Self::ioctl)

        } else {