moss-kernel/src/fs/mod.rs

use alloc::boxed::Box;
use alloc::{collections::btree_map::BTreeMap, sync::Arc};
use async_trait::async_trait;
use core::sync::atomic::{AtomicU64, Ordering};
use dir::DirFile;
use libkernel::error::{FsError, KernelError, Result};
use libkernel::fs::attr::FilePermissions;
use libkernel::fs::path::Path;
use libkernel::fs::{BlockDevice, FS_ID_START, FileType, Filesystem, Inode, InodeId, OpenFlags};
use open_file::OpenFile;
use reg::RegFile;

use crate::drivers::{DM, Driver};
use crate::process::Task;
use crate::sync::SpinLock;
use alloc::vec::Vec;

pub mod dir;
pub mod fops;
pub mod open_file;
pub mod pipe;
pub mod reg;
pub mod syscalls;

/// A dummy inode used as a placeholder before the root filesystem is mounted.
pub struct DummyInode {}

impl Inode for DummyInode {
    fn id(&self) -> InodeId {
        InodeId::dummy()
    }
}

/// Represents a mounted filesystem.
struct Mount {
    fs: Arc<dyn Filesystem>,
    root_inode: Arc<dyn Inode>,
}

/// This trait represents a type of filesystem, like "ext4" or "tmpfs". It acts
/// as a factory for creating mounted instances.
#[async_trait]
pub trait FilesystemDriver: Driver + Send + Sync {
    async fn construct(
        &self,
        fs_id: u64,
        blk_dev: Option<Box<dyn BlockDevice>>,
    ) -> Result<Arc<dyn Filesystem>>;
}

/// The internal state of the VFS.
///
/// This struct consolidates the filesystem-wide collections (the list of all
/// registered filesystem instances and the mapping of mount points).
struct VfsState {
    /// A map from an InodeId of a directory to the Mount that is mounted there.
    mounts: BTreeMap<InodeId, Mount>,
    /// A map from a filesystem ID to the corresponding filesystem instance.
    filesystems: BTreeMap<u64, Arc<dyn Filesystem>>,
}

impl VfsState {
    /// Creates a new, empty VfsState.
    const fn new() -> Self {
        Self {
            mounts: BTreeMap::new(),
            filesystems: BTreeMap::new(),
        }
    }

    /// Registers a new filesystem and its mount point.
    fn add_mount(&mut self, mount_point_id: InodeId, mount: Mount) {
        self.filesystems.insert(mount.fs.id(), mount.fs.clone());
        self.mounts.insert(mount_point_id, mount);
    }

    /// Checks if an inode is a mount point and returns the root inode of the
    /// mounted filesystem if it is.
    fn get_mount_root(&self, inode_id: &InodeId) -> Option<Arc<dyn Inode>> {
        self.mounts
            .get(inode_id)
            .map(|mount| mount.root_inode.clone())
    }
}

#[allow(clippy::upper_case_acronyms)]
pub struct VFS {
    next_fs_id: AtomicU64,
    state: SpinLock<VfsState>,
    root_inode: SpinLock<Option<Arc<dyn Inode>>>,
}

impl VFS {
    const fn new() -> Self {
        Self {
            next_fs_id: AtomicU64::new(FS_ID_START),
            state: SpinLock::new(VfsState::new()),
            root_inode: SpinLock::new(None),
        }
    }

    /// Creates an instance of a filesystem from a registered driver.
    ///
    /// This does not mount the filesystem, but prepares an instance that can
    /// then be attached to a mount point.
    async fn create_fs_instance(
        &self,
        driver_name: &str,
        blkdev: Option<Box<dyn BlockDevice>>,
    ) -> Result<Arc<dyn Filesystem>> {
        let driver = DM
            .lock_save_irq()
            .find_by_name(driver_name)
            .ok_or(FsError::DriverNotFound)?
            .as_filesystem_driver()
            .ok_or(FsError::DriverNotFound)?;

        let id = self.next_fs_id.fetch_add(1, Ordering::SeqCst);

        driver.construct(id, blkdev).await
    }

    /// Mounts the root filesystem.
    pub async fn mount_root(
        &self,
        driver_name: &str,
        blkdev: Option<Box<dyn BlockDevice>>,
    ) -> Result<()> {
        let fs = self.create_fs_instance(driver_name, blkdev).await?;
        let root_inode = fs.root_inode().await?;

        let mount = Mount {
            fs,
            root_inode: root_inode.clone(),
        };

        // Lock the state to add the new mount and filesystem.
        self.state.lock_save_irq().add_mount(root_inode.id(), mount);

        // Set the global root inode.
        *self.root_inode.lock_save_irq() = Some(root_inode);

        Ok(())
    }

    /// Mounts a filesystem at a given directory (mount point).
    pub async fn mount(
        &self,
        mount_point: Arc<dyn Inode>,
        driver_name: &str,
        blkdev: Option<Box<dyn BlockDevice>>,
    ) -> Result<()> {
        if mount_point.getattr().await?.file_type != FileType::Directory {
            return Err(FsError::NotADirectory.into());
        }

        let fs = self.create_fs_instance(driver_name, blkdev).await?;
        let mount_point_id = mount_point.id();
        let root_inode = fs.root_inode().await?;

        let new_mount = Mount { fs, root_inode };

        // Lock the state and insert the new mount.
        self.state
            .lock_save_irq()
            .add_mount(mount_point_id, new_mount);

        Ok(())
    }

    /// Resolves a path string to an Inode, starting from a given root for
    /// relative paths.
    pub async fn resolve_path(
        &self,
        path: &Path,
        root: Arc<dyn Inode>,
        task: Arc<Task>,
    ) -> Result<Arc<dyn Inode>> {
        let mut current_inode = if path.is_absolute() {
            task.root.lock_save_irq().0.clone() // use the task's root inode, in case a custom chroot was set
        } else {
            root
        };

        for component in path.components() {
            // Before looking up the component, check if the current inode is a
            // mount point. If so, traverse into the mounted filesystem's root.
            if let Some(mount_root) = self
                .state
                .lock_save_irq()
                .get_mount_root(&current_inode.id())
            {
                current_inode = mount_root;
            }

            // Delegate the lookup to the underlying filesystem.
            current_inode = current_inode.lookup(component).await?;
        }

        // After the final lookup, check if the destination is itself a mount point.
        if let Some(mount_root) = self
            .state
            .lock_save_irq()
            .get_mount_root(&current_inode.id())
        {
            current_inode = mount_root;
        }

        Ok(current_inode)
    }

    /// Resolves a path string to an Inode, starting from a given root for
    /// relative paths, and using the filesystem root inode for absolute paths.
    pub async fn resolve_path_absolute(
        &self,
        path: &Path,
        root: Arc<dyn Inode>,
    ) -> Result<Arc<dyn Inode>> {
        let mut current_inode = if path.is_absolute() {
            self.root_inode
                .lock_save_irq()
                .as_ref()
                .cloned()
                .ok_or(FsError::NotFound)?
        } else {
            root
        };

        for component in path.components() {
            // Before looking up the component, check if the current inode is a
            // mount point. If so, traverse into the mounted filesystem's root.
            if let Some(mount_root) = self
                .state
                .lock_save_irq()
                .get_mount_root(&current_inode.id())
            {
                current_inode = mount_root;
            }

            // Delegate the lookup to the underlying filesystem.
            current_inode = current_inode.lookup(component).await?;
        }

        // After the final lookup, check if the destination is itself a mount point.
        if let Some(mount_root) = self
            .state
            .lock_save_irq()
            .get_mount_root(&current_inode.id())
        {
            current_inode = mount_root;
        }

        Ok(current_inode)
    }

    /// Returns a clone of the root inode.
    pub fn root_inode(&self) -> Arc<dyn Inode> {
        self.root_inode.lock_save_irq().as_ref().unwrap().clone()
    }

    pub async fn open(
        &self,
        path: &Path,
        flags: OpenFlags,
        root: Arc<dyn Inode>,
        mode: FilePermissions,
        task: Arc<Task>,
    ) -> Result<Arc<OpenFile>> {
        // Attempt to resolve the full path first.
        let resolve_result = self.resolve_path(path, root.clone(), task.clone()).await;

        let target_inode = match resolve_result {
            // The file/directory exists.
            Ok(inode) => {
                if flags.contains(OpenFlags::O_CREAT | OpenFlags::O_EXCL) {
                    // O_CREAT and O_EXCL were passed and the file exists. This is
                    // an error.
                    return Err(FsError::AlreadyExists.into());
                }
                // The file exists, and we're not exclusively creating. Proceed.
                inode
            }

            // The path was not found.
            Err(KernelError::Fs(FsError::NotFound)) => {
                // If O_CREAT is specified, we should create it.
                if flags.contains(OpenFlags::O_CREAT) {
                    // Determine the target name and parent directory. If the path has no
                    // explicit parent component (e.g., "foo"), use the provided `root`
                    // (cwd or dirfd) as the parent directory.
                    let file_name = path.file_name().ok_or(FsError::InvalidInput)?;
                    let parent_inode = if let Some(parent_path) = path.parent() {
                        self.resolve_path(parent_path, root.clone(), task).await?
                    } else {
                        root.clone()
                    };

                    // Ensure the parent is actually a directory before creating a
                    // file in it.
                    if parent_inode.getattr().await?.file_type != FileType::Directory {
                        return Err(FsError::NotADirectory.into());
                    }

                    parent_inode.create(file_name, FileType::File, mode).await?
                } else {
                    // O_CREAT was not specified, so NotFound is the correct error.
                    return Err(FsError::NotFound.into());
                }
            }

            // Some other error occurred during resolution (e.g., NotADirectory
            // mid-path).
            Err(e) => return Err(e),
        };

        let attr = target_inode.getattr().await?;

        if flags.contains(OpenFlags::O_DIRECTORY) && attr.file_type != FileType::Directory {
            return Err(FsError::NotADirectory.into());
        }

        if attr.file_type == FileType::Directory
            && (flags.contains(OpenFlags::O_WRONLY) || flags.contains(OpenFlags::O_RDWR))
        {
            return Err(FsError::IsADirectory.into());
        }

        if flags.contains(OpenFlags::O_TRUNC)
            && attr.file_type == FileType::File
            && (flags.contains(OpenFlags::O_WRONLY) || flags.contains(OpenFlags::O_RDWR))
        {
            // TODO: Check for write permissions on the inode itself.
            target_inode.truncate(0).await?;
        }

        match attr.file_type {
            FileType::File => {
                let mut open_file =
                    OpenFile::new(Box::new(RegFile::new(target_inode.clone())), flags);
                open_file.set_inode(target_inode);

                Ok(Arc::new(open_file))
            }
            FileType::Directory => {
                let mut open_file =
                    OpenFile::new(Box::new(DirFile::new(target_inode.clone())), flags);
                open_file.set_inode(target_inode);

                Ok(Arc::new(open_file))
            }
            FileType::Symlink => todo!(),
            FileType::BlockDevice(_) => todo!(),
            FileType::CharDevice(char_dev_descriptor) => {
                let char_driver = DM
                    .lock_save_irq()
                    .find_char_driver(char_dev_descriptor.major)
                    .ok_or(FsError::NoDevice)?;

                Ok(char_driver
                    .get_device(char_dev_descriptor.minor)
                    .ok_or(FsError::NoDevice)?
                    .open(flags)?)
            }
            FileType::Fifo => todo!(),
            FileType::Socket => todo!(),
        }
    }

    pub async fn mkdir(
        &self,
        path: &Path,
        root: Arc<dyn Inode>,
        mode: FilePermissions,
        task: Arc<Task>,
    ) -> Result<()> {
        // Try to resolve the target directory first.
        match self.resolve_path(path, root.clone(), task.clone()).await {
            // The path already exists, this is an error.
            Ok(_) => Err(FsError::AlreadyExists.into()),

            // The path does not exist, we need to create it.
            Err(KernelError::Fs(FsError::NotFound)) => {
                // Determine the new directory name.
                let dir_name = path.file_name().ok_or(FsError::InvalidInput)?;

                // Resolve the parent directory.  If the path has no parent
                // component (e.g., \"foo\"), treat the provided `root`
                // directory (AT_FDCWD / cwd / dirfd) as the parent.
                let parent_inode = if let Some(parent_path) = path.parent() {
                    self.resolve_path(parent_path, root.clone(), task).await?
                } else {
                    root.clone()
                };

                // Verify that the parent is actually a directory.
                if parent_inode.getattr().await?.file_type != FileType::Directory {
                    return Err(FsError::NotADirectory.into());
                }

                // Delegate the creation to the filesystem-specific inode.
                parent_inode
                    .create(dir_name, FileType::Directory, mode)
                    .await?;

                Ok(())
            }

            // Propagate any other errors up the stack.
            Err(e) => Err(e),
        }
    }

    pub async fn unlink(
        &self,
        path: &Path,
        root: Arc<dyn Inode>,
        remove_dir: bool,
        task: Arc<Task>,
    ) -> Result<()> {
        // First, resolve the target inode so we can inspect its type.
        let target_inode = self.resolve_path(path, root.clone(), task.clone()).await?;

        let attr = target_inode.getattr().await?;

        // Validate flag and file-type combinations.
        match attr.file_type {
            FileType::Directory if !remove_dir => {
                return Err(FsError::IsADirectory.into());
            }
            FileType::Directory => { /* OK: rmdir semantics */ }
            _ if remove_dir => {
                return Err(FsError::NotADirectory.into());
            }
            _ => { /* Regular unlink */ }
        }

        // Determine the parent directory inode in which to perform the unlink.
        let parent_inode = if let Some(parent_path) = path.parent() {
            self.resolve_path(parent_path, root.clone(), task).await?
        } else {
            root.clone()
        };

        // Ensure the parent really is a directory.
        if parent_inode.getattr().await?.file_type != FileType::Directory {
            return Err(FsError::NotADirectory.into());
        }

        // Extract the final component (name) and perform the unlink on the parent.
        let name = path.file_name().ok_or(FsError::InvalidInput)?;

        parent_inode.unlink(name).await?;

        Ok(())
    }
}

pub static VFS: VFS = VFS::new();

impl VFS {
    /// Flushes all mounted filesystems and their underlying block devices.
    /// Any individual error is logged and ignored so that a single faulty
    /// filesystem does not block the shutdown sequence.
    pub async fn sync_all(&self) -> Result<()> {
        let filesystems: Vec<_> = {
            let state = self.state.lock_save_irq();
            state.filesystems.values().cloned().collect()
        };

        for fs in filesystems {
            // Ignore per-filesystem errors; best-effort
            let _ = fs.sync().await;
        }

        Ok(())
    }
}