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Diffstat (limited to 'rust/kernel/debugfs/file_ops.rs')
| -rw-r--r-- | rust/kernel/debugfs/file_ops.rs | 385 |
1 files changed, 385 insertions, 0 deletions
diff --git a/rust/kernel/debugfs/file_ops.rs b/rust/kernel/debugfs/file_ops.rs new file mode 100644 index 000000000000..8a0442d6dd7a --- /dev/null +++ b/rust/kernel/debugfs/file_ops.rs @@ -0,0 +1,385 @@ +// SPDX-License-Identifier: GPL-2.0 +// Copyright (C) 2025 Google LLC. + +use super::{BinaryReader, BinaryWriter, Reader, Writer}; +use crate::debugfs::callback_adapters::Adapter; +use crate::fmt; +use crate::fs::file; +use crate::prelude::*; +use crate::seq_file::SeqFile; +use crate::seq_print; +use crate::uaccess::UserSlice; +use core::marker::PhantomData; + +#[cfg(CONFIG_DEBUG_FS)] +use core::ops::Deref; + +/// # Invariant +/// +/// `FileOps<T>` will always contain an `operations` which is safe to use for a file backed +/// off an inode which has a pointer to a `T` in its private data that is safe to convert +/// into a reference. +pub(super) struct FileOps<T> { + #[cfg(CONFIG_DEBUG_FS)] + operations: bindings::file_operations, + #[cfg(CONFIG_DEBUG_FS)] + mode: u16, + _phantom: PhantomData<T>, +} + +impl<T> FileOps<T> { + /// # Safety + /// + /// The caller asserts that the provided `operations` is safe to use for a file whose + /// inode has a pointer to `T` in its private data that is safe to convert into a reference. + const unsafe fn new(operations: bindings::file_operations, mode: u16) -> Self { + Self { + #[cfg(CONFIG_DEBUG_FS)] + operations, + #[cfg(CONFIG_DEBUG_FS)] + mode, + _phantom: PhantomData, + } + } + + #[cfg(CONFIG_DEBUG_FS)] + pub(crate) const fn mode(&self) -> u16 { + self.mode + } +} + +impl<T: Adapter> FileOps<T> { + pub(super) const fn adapt(&self) -> &FileOps<T::Inner> { + // SAFETY: `Adapter` asserts that `T` can be legally cast to `T::Inner`. + unsafe { core::mem::transmute(self) } + } +} + +#[cfg(CONFIG_DEBUG_FS)] +impl<T> Deref for FileOps<T> { + type Target = bindings::file_operations; + + fn deref(&self) -> &Self::Target { + &self.operations + } +} + +struct WriterAdapter<T>(T); + +impl<'a, T: Writer> fmt::Display for WriterAdapter<&'a T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + self.0.write(f) + } +} + +/// Implements `open` for `file_operations` via `single_open` to fill out a `seq_file`. +/// +/// # Safety +/// +/// * `inode`'s private pointer must point to a value of type `T` which will outlive the `inode` +/// and will not have any unique references alias it during the call. +/// * `file` must point to a live, not-yet-initialized file object. +unsafe extern "C" fn writer_open<T: Writer + Sync>( + inode: *mut bindings::inode, + file: *mut bindings::file, +) -> c_int { + // SAFETY: The caller ensures that `inode` is a valid pointer. + let data = unsafe { (*inode).i_private }; + // SAFETY: + // * `file` is acceptable by caller precondition. + // * `print_act` will be called on a `seq_file` with private data set to the third argument, + // so we meet its safety requirements. + // * The `data` pointer passed in the third argument is a valid `T` pointer that outlives + // this call by caller preconditions. + unsafe { bindings::single_open(file, Some(writer_act::<T>), data) } +} + +/// Prints private data stashed in a seq_file to that seq file. +/// +/// # Safety +/// +/// `seq` must point to a live `seq_file` whose private data is a valid pointer to a `T` which may +/// not have any unique references alias it during the call. +unsafe extern "C" fn writer_act<T: Writer + Sync>( + seq: *mut bindings::seq_file, + _: *mut c_void, +) -> c_int { + // SAFETY: By caller precondition, this pointer is valid pointer to a `T`, and + // there are not and will not be any unique references until we are done. + let data = unsafe { &*((*seq).private.cast::<T>()) }; + // SAFETY: By caller precondition, `seq_file` points to a live `seq_file`, so we can lift + // it. + let seq_file = unsafe { SeqFile::from_raw(seq) }; + seq_print!(seq_file, "{}", WriterAdapter(data)); + 0 +} + +// Work around lack of generic const items. +pub(crate) trait ReadFile<T> { + const FILE_OPS: FileOps<T>; +} + +impl<T: Writer + Sync> ReadFile<T> for T { + const FILE_OPS: FileOps<T> = { + let operations = bindings::file_operations { + read: Some(bindings::seq_read), + llseek: Some(bindings::seq_lseek), + release: Some(bindings::single_release), + open: Some(writer_open::<Self>), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; + // SAFETY: `operations` is all stock `seq_file` implementations except for `writer_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 matches the + // `FileOps` requirements. + unsafe { FileOps::new(operations, 0o400) } + }; +} + +fn read<T: Reader + Sync>(data: &T, buf: *const c_char, count: usize) -> isize { + let mut reader = UserSlice::new(UserPtr::from_ptr(buf as *mut c_void), count).reader(); + + if let Err(e) = data.read_from_slice(&mut reader) { + return e.to_errno() as isize; + } + + count as isize +} + +/// # Safety +/// +/// `file` must be a valid pointer to a `file` struct. +/// The `private_data` of the file must contain a valid pointer to a `seq_file` whose +/// `private` data in turn points to a `T` that implements `Reader`. +/// `buf` must be a valid user-space buffer. +pub(crate) unsafe extern "C" fn write<T: Reader + Sync>( + file: *mut bindings::file, + buf: *const c_char, + count: usize, + _ppos: *mut bindings::loff_t, +) -> isize { + // SAFETY: The file was opened with `single_open`, which sets `private_data` to a `seq_file`. + let seq = unsafe { &mut *((*file).private_data.cast::<bindings::seq_file>()) }; + // SAFETY: By caller precondition, this pointer is live and points to a value of type `T`. + let data = unsafe { &*(seq.private as *const T) }; + read(data, buf, count) +} + +// A trait to get the file operations for a type. +pub(crate) trait ReadWriteFile<T> { + const FILE_OPS: FileOps<T>; +} + +impl<T: Writer + Reader + Sync> ReadWriteFile<T> for T { + const FILE_OPS: FileOps<T> = { + let operations = bindings::file_operations { + open: Some(writer_open::<T>), + read: Some(bindings::seq_read), + write: Some(write::<T>), + llseek: Some(bindings::seq_lseek), + release: Some(bindings::single_release), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; + // SAFETY: `operations` is all stock `seq_file` implementations except for `writer_open` + // and `write`. + // `writer_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 matches the + // `FileOps` requirements. + // `write` only requires that the file's private data pointer points to `seq_file` + // which points to a `T` that will outlive it, which matches what `writer_open` + // provides. + unsafe { FileOps::new(operations, 0o600) } + }; +} + +/// # Safety +/// +/// `inode` must be a valid pointer to an `inode` struct. +/// `file` must be a valid pointer to a `file` struct. +unsafe extern "C" fn write_only_open( + inode: *mut bindings::inode, + file: *mut bindings::file, +) -> c_int { + // SAFETY: The caller ensures that `inode` and `file` are valid pointers. + unsafe { (*file).private_data = (*inode).i_private }; + 0 +} + +/// # Safety +/// +/// * `file` must be a valid pointer to a `file` struct. +/// * The `private_data` of the file must contain a valid pointer to a `T` that implements +/// `Reader`. +/// * `buf` must be a valid user-space buffer. +pub(crate) unsafe extern "C" fn write_only_write<T: Reader + Sync>( + file: *mut bindings::file, + buf: *const c_char, + count: usize, + _ppos: *mut bindings::loff_t, +) -> isize { + // SAFETY: The caller ensures that `file` is a valid pointer and that `private_data` holds a + // valid pointer to `T`. + let data = unsafe { &*((*file).private_data as *const T) }; + read(data, buf, count) +} + +pub(crate) trait WriteFile<T> { + const FILE_OPS: FileOps<T>; +} + +impl<T: Reader + Sync> WriteFile<T> for T { + const FILE_OPS: FileOps<T> = { + let operations = bindings::file_operations { + open: Some(write_only_open), + write: Some(write_only_write::<T>), + llseek: Some(bindings::noop_llseek), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; + // SAFETY: + // * `write_only_open` populates the file private data with the inode private data + // * `write_only_write`'s only requirement is that the private data of the file point to + // a `T` and be legal to convert to a shared reference, which `write_only_open` + // satisfies. + unsafe { FileOps::new(operations, 0o200) } + }; +} + +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 = unsafe { &*((*file).private_data.cast::<T>()) }; + + // SAFETY: + // - `ppos` is a valid `file::Offset` pointer. + // - We have exclusive access to `ppos`. + let pos: &mut file::Offset = unsafe { &mut *ppos }; + + let mut writer = UserSlice::new(UserPtr::from_ptr(buf.cast()), count).writer(); + + let ret = || -> Result<isize> { + let written = this.write_to_slice(&mut writer, pos)?; + + Ok(written.try_into()?) + }(); + + match ret { + Ok(n) => n, + Err(e) => e.to_errno() as isize, + } +} + +/// Representation of [`FileOps`] for read only binary files. +pub(crate) trait BinaryReadFile<T> { + const FILE_OPS: FileOps<T>; +} + +impl<T: BinaryWriter + Sync> BinaryReadFile<T> for T { + const FILE_OPS: FileOps<T> = { + let operations = bindings::file_operations { + read: Some(blob_read::<T>), + llseek: Some(bindings::default_llseek), + open: Some(bindings::simple_open), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; + + // SAFETY: + // - The private data of `struct inode` does always contain a pointer to a valid `T`. + // - `simple_open()` stores the `struct inode`'s private data in the private data of the + // corresponding `struct file`. + // - `blob_read()` re-creates a reference to `T` from the `struct file`'s private data. + // - `default_llseek()` does not access the `struct file`'s private data. + unsafe { FileOps::new(operations, 0o400) } + }; +} + +extern "C" fn blob_write<T: BinaryReader>( + file: *mut bindings::file, + buf: *const 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 = unsafe { &*((*file).private_data.cast::<T>()) }; + + // SAFETY: + // - `ppos` is a valid `file::Offset` pointer. + // - We have exclusive access to `ppos`. + let pos: &mut file::Offset = unsafe { &mut *ppos }; + + let mut reader = UserSlice::new(UserPtr::from_ptr(buf.cast_mut().cast()), count).reader(); + + let ret = || -> Result<isize> { + let read = this.read_from_slice(&mut reader, pos)?; + + Ok(read.try_into()?) + }(); + + match ret { + Ok(n) => n, + Err(e) => e.to_errno() as isize, + } +} + +/// Representation of [`FileOps`] for write only binary files. +pub(crate) trait BinaryWriteFile<T> { + const FILE_OPS: FileOps<T>; +} + +impl<T: BinaryReader + Sync> BinaryWriteFile<T> for T { + const FILE_OPS: FileOps<T> = { + let operations = bindings::file_operations { + write: Some(blob_write::<T>), + llseek: Some(bindings::default_llseek), + open: Some(bindings::simple_open), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; + + // SAFETY: + // - The private data of `struct inode` does always contain a pointer to a valid `T`. + // - `simple_open()` stores the `struct inode`'s private data in the private data of the + // corresponding `struct file`. + // - `blob_write()` re-creates a reference to `T` from the `struct file`'s private data. + // - `default_llseek()` does not access the `struct file`'s private data. + unsafe { FileOps::new(operations, 0o200) } + }; +} + +/// Representation of [`FileOps`] for read/write binary files. +pub(crate) trait BinaryReadWriteFile<T> { + const FILE_OPS: FileOps<T>; +} + +impl<T: BinaryWriter + BinaryReader + Sync> BinaryReadWriteFile<T> for T { + const FILE_OPS: FileOps<T> = { + let operations = bindings::file_operations { + read: Some(blob_read::<T>), + write: Some(blob_write::<T>), + llseek: Some(bindings::default_llseek), + open: Some(bindings::simple_open), + // SAFETY: `file_operations` supports zeroes in all fields. + ..unsafe { core::mem::zeroed() } + }; + + // SAFETY: + // - The private data of `struct inode` does always contain a pointer to a valid `T`. + // - `simple_open()` stores the `struct inode`'s private data in the private data of the + // corresponding `struct file`. + // - `blob_read()` re-creates a reference to `T` from the `struct file`'s private data. + // - `blob_write()` re-creates a reference to `T` from the `struct file`'s private data. + // - `default_llseek()` does not access the `struct file`'s private data. + unsafe { FileOps::new(operations, 0o600) } + }; +} |