On 23/10/18 09:25AM, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@xxxxxxxxxxxxx>
>
> Allow Rust file systems to associate [typed] data to super blocks when
> they're created. Since we only have a pointer-sized field in which to
> store the state, it must implement the `ForeignOwnable` trait.
>
> Signed-off-by: Wedson Almeida Filho <walmeida@xxxxxxxxxxxxx>
> ---
> rust/kernel/fs.rs | 42 +++++++++++++++++++++++++++++++++------
> samples/rust/rust_rofs.rs | 4 +++-
> 2 files changed, 39 insertions(+), 7 deletions(-)
>
> diff --git a/rust/kernel/fs.rs b/rust/kernel/fs.rs
> index 5b7eaa16d254..e9a9362d2897 100644
> --- a/rust/kernel/fs.rs
> +++ b/rust/kernel/fs.rs
> @@ -7,7 +7,7 @@
> //! C headers: [`include/linux/fs.h`](../../include/linux/fs.h)
>
> use crate::error::{code::*, from_result, to_result, Error, Result};
> -use crate::types::{ARef, AlwaysRefCounted, Either, Opaque};
> +use crate::types::{ARef, AlwaysRefCounted, Either, ForeignOwnable, Opaque};
> use crate::{
> bindings, folio::LockedFolio, init::PinInit, str::CStr, time::Timespec, try_pin_init,
> ThisModule,
> @@ -20,11 +20,14 @@
>
> /// A file system type.
> pub trait FileSystem {
> + /// Data associated with each file system instance (super-block).
> + type Data: ForeignOwnable + Send + Sync;
> +
> /// The name of the file system type.
> const NAME: &'static CStr;
>
> /// Returns the parameters to initialise a super block.
> - fn super_params(sb: &NewSuperBlock<Self>) -> Result<SuperParams>;
> + fn super_params(sb: &NewSuperBlock<Self>) -> Result<SuperParams<Self::Data>>;
>
> /// Initialises and returns the root inode of the given superblock.
> ///
> @@ -174,7 +177,7 @@ pub fn new<T: FileSystem + ?Sized>(module: &'static ThisModule) -> impl PinInit<
> fs.owner = module.0;
> fs.name = T::NAME.as_char_ptr();
> fs.init_fs_context = Some(Self::init_fs_context_callback::<T>);
> - fs.kill_sb = Some(Self::kill_sb_callback);
> + fs.kill_sb = Some(Self::kill_sb_callback::<T>);
> fs.fs_flags = 0;
>
> // SAFETY: Pointers stored in `fs` are static so will live for as long as the
> @@ -195,10 +198,22 @@ pub fn new<T: FileSystem + ?Sized>(module: &'static ThisModule) -> impl PinInit<
> })
> }
>
> - unsafe extern "C" fn kill_sb_callback(sb_ptr: *mut bindings::super_block) {
> + unsafe extern "C" fn kill_sb_callback<T: FileSystem + ?Sized>(
> + sb_ptr: *mut bindings::super_block,
> + ) {
> // SAFETY: In `get_tree_callback` we always call `get_tree_nodev`, so `kill_anon_super` is
> // the appropriate function to call for cleanup.
> unsafe { bindings::kill_anon_super(sb_ptr) };
> +
> + // SAFETY: The C API contract guarantees that `sb_ptr` is valid for read.
> + let ptr = unsafe { (*sb_ptr).s_fs_info };
> + if !ptr.is_null() {
> + // SAFETY: The only place where `s_fs_info` is assigned is `NewSuperBlock::init`, where
> + // it's initialised with the result of an `into_foreign` call. We checked above that
> + // `ptr` is non-null because it would be null if we never reached the point where we
> + // init the field.
> + unsafe { T::Data::from_foreign(ptr) };
> + }
> }
> }
>
> @@ -429,6 +444,14 @@ pub struct INodeParams {
> pub struct SuperBlock<T: FileSystem + ?Sized>(Opaque<bindings::super_block>, PhantomData<T>);
>
> impl<T: FileSystem + ?Sized> SuperBlock<T> {
> + /// Returns the data associated with the superblock.
> + pub fn data(&self) -> <T::Data as ForeignOwnable>::Borrowed<'_> {
> + // SAFETY: This method is only available after the `NeedsData` typestate, so `s_fs_info`
`NeedsData` typestate no longer exists in your latest patch version.
Cheers,
Ariel
> + // has been initialised initialised with the result of a call to `T::into_foreign`.
> + let ptr = unsafe { (*self.0.get()).s_fs_info };
> + unsafe { T::Data::borrow(ptr) }
> + }
> +
> /// Tries to get an existing inode or create a new one if it doesn't exist yet.
> pub fn get_or_create_inode(&self, ino: Ino) -> Result<Either<ARef<INode<T>>, NewINode<T>>> {
> // SAFETY: The only initialisation missing from the superblock is the root, and this
> @@ -458,7 +481,7 @@ pub fn get_or_create_inode(&self, ino: Ino) -> Result<Either<ARef<INode<T>>, New
> /// Required superblock parameters.
> ///
> /// This is returned by implementations of [`FileSystem::super_params`].
> -pub struct SuperParams {
> +pub struct SuperParams<T: ForeignOwnable + Send + Sync> {
> /// The magic number of the superblock.
> pub magic: u32,
>
> @@ -472,6 +495,9 @@ pub struct SuperParams {
>
> /// Granularity of c/m/atime in ns (cannot be worse than a second).
> pub time_gran: u32,
> +
> + /// Data to be associated with the superblock.
> + pub data: T,
> }
>
> /// A superblock that is still being initialised.
> @@ -522,6 +548,9 @@ impl<T: FileSystem + ?Sized> Tables<T> {
> sb.0.s_blocksize = 1 << sb.0.s_blocksize_bits;
> sb.0.s_flags |= bindings::SB_RDONLY;
>
> + // N.B.: Even on failure, `kill_sb` is called and frees the data.
> + sb.0.s_fs_info = params.data.into_foreign().cast_mut();
> +
> // SAFETY: The callback contract guarantees that `sb_ptr` is a unique pointer to a
> // newly-created (and initialised above) superblock.
> let sb = unsafe { &mut *sb_ptr.cast() };
> @@ -934,8 +963,9 @@ fn init(module: &'static ThisModule) -> impl PinInit<Self, Error> {
> ///
> /// struct MyFs;
> /// impl fs::FileSystem for MyFs {
> +/// type Data = ();
> /// const NAME: &'static CStr = c_str!("myfs");
> -/// fn super_params(_: &NewSuperBlock<Self>) -> Result<SuperParams> {
> +/// fn super_params(_: &NewSuperBlock<Self>) -> Result<SuperParams<Self::Data>> {
> /// todo!()
> /// }
> /// fn init_root(_sb: &SuperBlock<Self>) -> Result<ARef<INode<Self>>> {
> diff --git a/samples/rust/rust_rofs.rs b/samples/rust/rust_rofs.rs
> index 95ce28efa1c3..093425650f26 100644
> --- a/samples/rust/rust_rofs.rs
> +++ b/samples/rust/rust_rofs.rs
> @@ -52,14 +52,16 @@ struct Entry {
>
> struct RoFs;
> impl fs::FileSystem for RoFs {
> + type Data = ();
> const NAME: &'static CStr = c_str!("rust-fs");
>
> - fn super_params(_sb: &NewSuperBlock<Self>) -> Result<SuperParams> {
> + fn super_params(_sb: &NewSuperBlock<Self>) -> Result<SuperParams<Self::Data>> {
> Ok(SuperParams {
> magic: 0x52555354,
> blocksize_bits: 12,
> maxbytes: fs::MAX_LFS_FILESIZE,
> time_gran: 1,
> + data: (),
> })
> }
>
> --
> 2.34.1
>
