starry-kernel 0.5.10

use alloc::sync::Arc;
use core::ffi::{c_char, c_void};

use ax_errno::{AxError, AxResult, LinuxError};
use ax_fs::{FS_CONTEXT, is_mount_busy as fs_is_mount_busy};

use crate::{
    file::{Directory, FD_TABLE, File, FileLike},
    mm::vm_load_string,
    pseudofs::MemoryFs,
    task::{AsThread, tasks},
};

fn fd_points_to_mount(fd: &dyn FileLike, mp: &Arc<axfs_ng_vfs::Mountpoint>) -> bool {
    fd.downcast_ref::<File>()
        .is_some_and(|f| Arc::ptr_eq(f.inner().location().mountpoint(), mp))
        || fd
            .downcast_ref::<Directory>()
            .is_some_and(|d| Arc::ptr_eq(d.inner().mountpoint(), mp))
}

fn is_mount_busy(mp: &Arc<axfs_ng_vfs::Mountpoint>) -> bool {
    if fs_is_mount_busy(mp) {
        return true;
    }
    for task in tasks() {
        let Some(thread) = task.try_as_thread() else {
            continue;
        };
        let scope = thread.proc_data.scope.read();
        let fd_table = FD_TABLE.scope(&scope).clone();
        drop(scope);
        let table = fd_table.read();
        if table.ids().any(|id| {
            table
                .get(id)
                .is_some_and(|fd| fd_points_to_mount(&*fd.inner, mp))
        }) {
            return true;
        }
    }
    false
}

pub fn sys_mount(
    source: *const c_char,
    target: *const c_char,
    fs_type: *const c_char,
    _flags: i32,
    _data: *const c_void,
) -> AxResult<isize> {
    let source = vm_load_string(source)?;
    let target = vm_load_string(target)?;
    let fs_type = vm_load_string(fs_type)?;
    debug!("sys_mount <= source: {source:?}, target: {target:?}, fs_type: {fs_type:?}");

    match fs_type.as_str() {
        "tmpfs" => {
            let fs = MemoryFs::new();
            let target = FS_CONTEXT.lock().resolve(target)?;
            target.mount(&fs)?;
        }
        #[cfg(feature = "ext4")]
        "ext4" => {
            mount_ext4(&source, &target)?;
        }
        _ => return Err(AxError::NoSuchDevice),
    }

    Ok(0)
}

#[cfg(feature = "ext4")]
fn mount_ext4(source: &str, target: &str) -> AxResult<()> {
    use alloc::{boxed::Box, sync::Arc};

    use ax_driver::prelude::BlockDriverOps;

    let ctx = FS_CONTEXT.lock();

    // Resolve source device path (e.g., "/dev/loop0") to a block device
    let source_loc = ctx.resolve(source)?;
    let device = source_loc
        .entry()
        .downcast::<crate::pseudofs::Device>()
        .map_err(|_| {
            warn!("mount_ext4: {:?} is not a device", source);
            AxError::NoSuchDevice
        })?;
    let loop_dev = device
        .inner()
        .as_any()
        .downcast_ref::<crate::pseudofs::dev::LoopDevice>()
        .ok_or_else(|| {
            warn!("mount_ext4: {:?} is not a loop device", source);
            AxError::NoSuchDevice
        })?;
    let block_dev = loop_dev.as_dyn_block_device().inspect_err(|e| {
        warn!(
            "mount_ext4: loop device as_dyn_block_device failed: {:?}",
            e
        );
    })?;

    let num_blocks = block_dev.num_blocks();
    let region = ax_driver::PartitionRegion::from_num_blocks(num_blocks);

    // Create ext4 filesystem from the dynamic block device
    let fs = ax_fs::new_filesystem_from_dyn(block_dev, region).map_err(|e| {
        warn!("mount_ext4: failed to create ext4 filesystem: {:?}", e);
        AxError::Io
    })?;

    // Mount at the target location
    let target_loc = ctx.resolve(target)?;
    target_loc.mount(&fs).map_err(|e| {
        warn!("mount_ext4: failed to mount at {:?}: {:?}", target, e);
        AxError::Io
    })?;

    // Store a writeback callback in the mount root's user_data so that
    // sys_umount2 can flush the loop device's block cache to the backing
    // file after the filesystem is unmounted.
    let ops: Arc<dyn crate::pseudofs::DeviceOps> = device.inner().clone();
    {
        let mount_root = ctx.resolve(target)?;
        mount_root.user_data().insert(Box::new(move || {
            if let Some(ld) = ops
                .as_any()
                .downcast_ref::<crate::pseudofs::dev::LoopDevice>()
            {
                ld.flush_cache_to_file()
            } else {
                Ok(())
            }
        }) as Box<dyn Fn() -> AxResult<()> + Send + Sync>);
    }

    Ok(())
}

pub fn sys_umount2(target: *const c_char, _flags: i32) -> AxResult<isize> {
    use alloc::boxed::Box;

    let target = vm_load_string(target)?;
    debug!("sys_umount2 <= target: {target:?}");
    let target = FS_CONTEXT.lock().resolve(target)?;

    // Linux umount2 returns EINVAL for paths that are not mount points.
    if !target.is_root_of_mount() {
        return Err(AxError::InvalidInput);
    }

    // Linux umount2 returns EBUSY if any task has cwd/root or open fd
    // inside the mount.
    if is_mount_busy(target.mountpoint()) {
        return Err(AxError::from(LinuxError::EBUSY));
    }

    // Retrieve the writeback callback (if any) before unmount tears down
    // the mount.  For ext4-on-loop mounts this flushes the block device
    // cache to the backing file after the filesystem is unmounted; for
    // other filesystem types (tmpfs) the callback is absent.
    let writeback = {
        let ud = target.user_data();
        ud.get::<Box<dyn Fn() -> AxResult<()> + Send + Sync>>()
    }; // user_data lock released

    target.unmount()?;

    // After unmount the SpinNoPreempt lock inside ext4 is released; safe
    // to do VFS I/O here.  Propagate writeback errors so userspace sees
    // EIO when dirty data could not be persisted to the backing file.
    if let Some(cb) = writeback {
        cb()?;
    }

    Ok(0)
}

pub fn sys_pivot_root(new_root: *const c_char, put_old: *const c_char) -> AxResult<isize> {
    let new_root = vm_load_string(new_root)?;
    let put_old = vm_load_string(put_old)?;
    debug!(
        "sys_pivot_root <= new_root: {:?}, put_old: {:?}",
        new_root, put_old
    );

    // Validate: put_old must be at or under new_root (path-separator-aware
    // so that "/new" does not falsely match "/newroot/old").
    let nr = new_root.trim_end_matches('/');
    let nr_slash = alloc::format!("{}/", nr);
    if !(put_old == nr || put_old.starts_with(&nr_slash)) {
        return Err(AxError::InvalidInput);
    }
    // new_root cannot be "/"
    if new_root == "/" {
        return Err(AxError::InvalidInput);
    }

    let mut ctx = FS_CONTEXT.lock();

    // The caller's current root must itself be a mount point (Linux
    // EINVAL if e.g. the process chroot'd into a subdirectory).
    if !ctx.root_dir().is_root_of_mount() {
        return Err(AxError::InvalidInput);
    }

    // Resolve paths
    let new_root_loc = ctx.resolve(&new_root)?;

    // Both must be directories
    new_root_loc.check_is_dir()?;
    let put_old_loc = ctx.resolve(&put_old)?;
    put_old_loc.check_is_dir()?;

    // new_root must be the root of a non-root mount (i.e. the root of a
    // filesystem mounted somewhere, not the global root).  Because path
    // resolution crosses mount boundaries transparently, the resolved
    // Location is the *root entry* of the mounted filesystem, so we check
    // is_root_of_mount + the mountpoint is not the global root.
    if !(new_root_loc.is_root_of_mount() && !new_root_loc.mountpoint().is_root()) {
        warn!(
            "sys_pivot_root: new_root {:?} is not the root of a mounted filesystem",
            new_root
        );
        return Err(AxError::InvalidInput);
    }

    // Capture the old root Location BEFORE the pivot, so that we can
    // propagate the change to every other task afterwards (Linux
    // chroot_fs_refs semantics).  We save the full Location (mountpoint +
    // dentry) rather than just the mountpoint, so that tasks chroot'd
    // into a subdirectory of the old root are not incorrectly updated.
    let old_root = ctx.root_dir().clone();

    // Perform pivot: swap the root mount (updates this task's FsContext).
    ctx.pivot_root(new_root_loc, put_old_loc)?;

    let new_root_loc = ctx.root_dir().clone();
    drop(ctx); // Release this task's lock before touching others.

    // Propagate root / cwd to all other tasks whose root_dir or current_dir
    // exactly matches the old root Location — mirroring Linux
    // chroot_fs_refs() in fs/namespace.c.
    ax_fs::FsContext::propagate_pivot_root(&old_root, &new_root_loc);

    Ok(0)
}