ZeroOS/src/fs/vfs.rs

const MAX_VFS_NODES: usize = 1024;
const MAX_FDS: usize = 512;
const MAX_AUTO_VFS_FDS: usize = 256;
const MAX_PATH: usize = 256;

pub const AT_FDCWD: isize = -100;

const S_IFDIR: u32 = 0o040000;
const S_IFCHR: u32 = 0o020000;
const S_IFREG: u32 = 0o100000;

const EBADF: isize = 9;
const EFAULT: isize = 14;
const EINVAL: isize = 22;
const ENOENT: isize = 2;
const ENOTDIR: isize = 20;
const EMFILE: isize = 24;

#[derive(Clone, Copy, PartialEq, Eq)]
enum Color {
    Red,
    Black,
}

#[derive(Clone, Copy, PartialEq, Eq)]
pub enum NodeKind {
    Directory,
    Regular,
    CharDevice,
}

#[derive(Clone, Copy)]
struct VfsNode {
    path: [u8; MAX_PATH],
    kind: NodeKind,
    data: *const u8,
    len: usize,
    parent: Option<usize>,
    left: Option<usize>,
    right: Option<usize>,
    color: Color,
}

impl VfsNode {
    const fn empty() -> Self {
        Self {
            path: [0; MAX_PATH],
            kind: NodeKind::Regular,
            data: core::ptr::null(),
            len: 0,
            parent: None,
            left: None,
            right: None,
            color: Color::Black,
        }
    }
}

#[derive(Clone, Copy)]
struct FileDescriptor {
    node: Option<usize>,
    offset: usize,
}

impl FileDescriptor {
    const fn empty() -> Self {
        Self {
            node: None,
            offset: 0,
        }
    }
}

pub struct Vfs {
    root: Option<usize>,
    nodes: [VfsNode; MAX_VFS_NODES],
    len: usize,
    fds: [FileDescriptor; MAX_FDS],
    cwd: [u8; MAX_PATH],
}

impl Vfs {
    const fn new() -> Self {
        Self {
            root: None,
            nodes: [VfsNode::empty(); MAX_VFS_NODES],
            len: 0,
            fds: [FileDescriptor::empty(); MAX_FDS],
            cwd: [0; MAX_PATH],
        }
    }

    fn reset(&mut self) {
        self.root = None;
        self.len = 0;
        self.fds.fill(FileDescriptor::empty());
        self.cwd = [0; MAX_PATH];
        self.cwd[0] = b'/';
    }

    fn insert(&mut self, path: &[u8], kind: NodeKind, data: *const u8, len: usize) -> Option<()> {
        if self.len >= MAX_VFS_NODES {
            return None;
        }

        let mut parent = None;
        let mut cursor = self.root;
        while let Some(index) = cursor {
            parent = cursor;
            match compare_path(path, &self.nodes[index].path) {
                core::cmp::Ordering::Less => cursor = self.nodes[index].left,
                core::cmp::Ordering::Greater => cursor = self.nodes[index].right,
                core::cmp::Ordering::Equal => {
                    self.nodes[index].kind = kind;
                    self.nodes[index].data = data;
                    self.nodes[index].len = len;
                    return Some(());
                }
            }
        }

        let index = self.len;
        self.len += 1;
        let mut stored_path = [0u8; MAX_PATH];
        let path_len = nul_len(path).min(MAX_PATH - 1);
        stored_path[..path_len].copy_from_slice(&path[..path_len]);

        self.nodes[index] = VfsNode {
            path: stored_path,
            kind,
            data,
            len,
            parent,
            left: None,
            right: None,
            color: Color::Red,
        };

        if let Some(parent) = parent {
            if compare_path(path, &self.nodes[parent].path).is_lt() {
                self.nodes[parent].left = Some(index);
            } else {
                self.nodes[parent].right = Some(index);
            }
        } else {
            self.root = Some(index);
        }

        self.insert_fixup(index);
        Some(())
    }

    fn find(&self, path: &[u8]) -> Option<usize> {
        let mut cursor = self.root;
        while let Some(index) = cursor {
            match compare_path(path, &self.nodes[index].path) {
                core::cmp::Ordering::Less => cursor = self.nodes[index].left,
                core::cmp::Ordering::Greater => cursor = self.nodes[index].right,
                core::cmp::Ordering::Equal => return Some(index),
            }
        }

        None
    }

    fn resolve_executable_path(&self, path: &[u8]) -> Option<usize> {
        let node = self.find(path);
        if let Some(index) = node {
            let node = self.nodes[index];
            if !(node.kind == NodeKind::Regular
                && node.len == 0
                && node.data.is_null()
                && is_busybox_applet_path(path))
            {
                return Some(index);
            }
        }
        self.busybox_fallback(path).or(node)
    }

    fn open_path(&mut self, path: &[u8]) -> isize {
        let Some(node) = self.resolve_executable_path(path) else {
            return -ENOENT;
        };

        for fd in 3..MAX_AUTO_VFS_FDS {
            if self.fds[fd].node.is_none() {
                self.fds[fd] = FileDescriptor {
                    node: Some(node),
                    offset: 0,
                };
                return fd as isize;
            }
        }

        -EMFILE
    }

    fn fd_dir_path(&self, fd: usize) -> Result<[u8; MAX_PATH], isize> {
        if fd >= MAX_FDS {
            return Err(-EBADF);
        }
        let Some(node) = self.fds[fd].node else {
            return Err(-EBADF);
        };
        if self.nodes[node].kind != NodeKind::Directory {
            return Err(-ENOTDIR);
        }
        Ok(self.nodes[node].path)
    }

    fn read_fd(&mut self, fd: usize, buffer: *mut u8, len: usize) -> isize {
        if fd >= MAX_FDS || buffer.is_null() {
            return -EBADF;
        }
        let Some(node_index) = self.fds[fd].node else {
            return -EBADF;
        };
        let node = self.nodes[node_index];
        if node.kind == NodeKind::CharDevice {
            let buffer = unsafe { core::slice::from_raw_parts_mut(buffer, len) };
            return crate::console::read(buffer) as isize;
        }
        if node.kind != NodeKind::Regular {
            return -EINVAL;
        }

        if node.data.is_null() {
            let count =
                match crate::fs::lwext4::read_path_at(&node.path, self.fds[fd].offset, buffer, len)
                {
                    Ok(count) => count,
                    Err(error) => return error,
                };
            self.fds[fd].offset = self.fds[fd].offset.saturating_add(count);
            return count as isize;
        }

        let node_len = self.node_len(node_index);
        let offset = self.fds[fd].offset.min(node_len);
        let available = node_len - offset;
        let count = len.min(available);
        if count > 0 {
            unsafe {
                let source = node.data.add(offset);
                core::ptr::copy_nonoverlapping(source, buffer, count);
            }
        }
        self.fds[fd].offset = offset + count;
        count as isize
    }

    fn write_fd(&mut self, fd: usize, buffer: *const u8, len: usize) -> isize {
        if fd >= MAX_FDS || buffer.is_null() {
            return -EBADF;
        }
        let Some(node_index) = self.fds[fd].node else {
            return -EBADF;
        };
        if self.nodes[node_index].kind == NodeKind::Regular {
            return self.write_regular_fd(fd, node_index, buffer, len);
        }
        if self.nodes[node_index].kind != NodeKind::CharDevice {
            return -EINVAL;
        }

        let buffer = unsafe { core::slice::from_raw_parts(buffer, len) };
        crate::console::write(buffer) as isize
    }

    fn write_regular_fd(
        &mut self,
        fd: usize,
        node_index: usize,
        buffer: *const u8,
        len: usize,
    ) -> isize {
        let offset = self.fds[fd].offset;
        let count = match crate::fs::lwext4::write_path_at(
            &self.nodes[node_index].path,
            offset,
            buffer,
            len,
        ) {
            Ok(count) => count,
            Err(error) => return error,
        };
        let end = offset.saturating_add(count);
        self.fds[fd].offset = end;
        if end > self.nodes[node_index].len {
            self.nodes[node_index].len = end;
        }
        count as isize
    }

    fn close_fd(&mut self, fd: usize) -> isize {
        if fd < 3 || fd >= MAX_FDS || self.fds[fd].node.is_none() {
            return -EBADF;
        }
        self.fds[fd] = FileDescriptor::empty();
        0
    }

    fn dup_fd(&mut self, oldfd: usize, min_newfd: usize) -> isize {
        if oldfd >= MAX_FDS || self.fds[oldfd].node.is_none() {
            return -EBADF;
        }
        let start = min_newfd.max(3);
        let end = if start < MAX_AUTO_VFS_FDS {
            MAX_AUTO_VFS_FDS
        } else {
            MAX_FDS
        };
        for fd in start..end {
            if self.fds[fd].node.is_none() {
                self.fds[fd] = self.fds[oldfd];
                return fd as isize;
            }
        }
        -EMFILE
    }

    fn dup2_fd(&mut self, oldfd: usize, newfd: usize) -> isize {
        if oldfd >= MAX_FDS || newfd >= MAX_FDS || self.fds[oldfd].node.is_none() {
            return -EBADF;
        }
        if oldfd == newfd {
            return newfd as isize;
        }
        self.fds[newfd] = self.fds[oldfd];
        newfd as isize
    }

    fn lseek_fd(&mut self, fd: usize, offset: isize, whence: usize) -> isize {
        if fd >= MAX_FDS {
            return -EBADF;
        }
        let Some(node_index) = self.fds[fd].node else {
            return -EBADF;
        };
        let len = self.node_len(node_index) as isize;
        let current = self.fds[fd].offset as isize;
        let next = match whence {
            0 => offset,
            1 => current.saturating_add(offset),
            2 => len.saturating_add(offset),
            _ => return -EINVAL,
        };
        if next < 0 {
            return -EINVAL;
        }
        self.fds[fd].offset = next as usize;
        next
    }

    fn stat_fd(&self, fd: usize, stat: *mut u8) -> isize {
        if fd >= MAX_FDS || stat.is_null() {
            return -EBADF;
        }
        let Some(node_index) = self.fds[fd].node else {
            return -EBADF;
        };
        write_stat(stat, self.nodes[node_index])
    }

    fn ftruncate_fd(&mut self, fd: usize, size: usize) -> isize {
        if fd >= MAX_FDS {
            return -EBADF;
        }
        let Some(node_index) = self.fds[fd].node else {
            return -EBADF;
        };
        if self.nodes[node_index].kind != NodeKind::Regular {
            return -EINVAL;
        }
        match crate::fs::lwext4::truncate_path(&self.nodes[node_index].path, size) {
            Ok(()) => {}
            Err(error) => return error,
        }
        self.nodes[node_index].len = size;
        0
    }

    fn is_tty_fd(&self, fd: usize) -> bool {
        if fd >= MAX_FDS {
            return false;
        }
        let Some(node_index) = self.fds[fd].node else {
            return false;
        };
        self.nodes[node_index].kind == NodeKind::CharDevice
    }

    fn getdents64_fd(&mut self, fd: usize, buffer: *mut u8, len: usize) -> isize {
        if fd >= MAX_FDS || buffer.is_null() {
            return -EBADF;
        }
        let Some(dir_index) = self.fds[fd].node else {
            return -EBADF;
        };
        let dir = self.nodes[dir_index];
        if dir.kind != NodeKind::Directory {
            return -ENOTDIR;
        }

        let mut written = 0usize;
        let mut cursor = self.fds[fd].offset;
        if cursor == 0 {
            if !write_dirent(buffer, len, &mut written, 1, NodeKind::Directory, b".") {
                return 0;
            }
            cursor = 1;
        }
        if cursor == 1 {
            if !write_dirent(buffer, len, &mut written, 2, NodeKind::Directory, b"..") {
                self.fds[fd].offset = 1;
                return written as isize;
            }
            cursor = 2;
        }
        while cursor < self.len {
            let node = self.nodes[cursor];
            cursor += 1;
            let Some(name) = child_name(&dir.path, &node.path) else {
                continue;
            };

            if !write_dirent(buffer, len, &mut written, cursor as u64, node.kind, name) {
                cursor -= 1;
                break;
            }
        }

        self.fds[fd].offset = cursor;
        written as isize
    }

    fn stat_path(&self, path: &[u8], stat: *mut u8) -> isize {
        if stat.is_null() {
            return -EFAULT;
        }
        let Some(node_index) = self.resolve_executable_path(path) else {
            return -ENOENT;
        };
        write_stat(stat, self.nodes[node_index])
    }

    fn truncate_path(&mut self, path: &[u8], size: usize) -> isize {
        let Some(node_index) = self.find(path) else {
            return -ENOENT;
        };
        if self.nodes[node_index].kind != NodeKind::Regular {
            return -EINVAL;
        }
        match crate::fs::lwext4::truncate_path(&self.nodes[node_index].path, size) {
            Ok(()) => {
                self.nodes[node_index].len = size;
                0
            }
            Err(error) => error,
        }
    }

    fn chdir_path(&mut self, path: &[u8]) -> isize {
        let Some(node_index) = self.find(path) else {
            return -ENOENT;
        };
        if self.nodes[node_index].kind != NodeKind::Directory {
            return -ENOTDIR;
        }
        self.cwd = [0; MAX_PATH];
        let path_len = nul_len(path).min(MAX_PATH - 1);
        self.cwd[..path_len].copy_from_slice(&path[..path_len]);
        if path_len == 0 {
            self.cwd[0] = b'/';
        }
        0
    }

    fn create_path(&mut self, path: &[u8], kind: NodeKind) -> isize {
        if self.find(path).is_some() {
            return 0;
        }
        if self.insert(path, kind, core::ptr::null(), 0).is_some() {
            0
        } else {
            -EMFILE
        }
    }

    fn node_len(&self, node_index: usize) -> usize {
        let node = self.nodes[node_index];
        if node.kind == NodeKind::Regular && node.data.is_null() {
            crate::fs::lwext4::size_path(&node.path).unwrap_or(node.len)
        } else {
            node.len
        }
    }

    fn getcwd(&self, buffer: *mut u8, len: usize) -> isize {
        if buffer.is_null() {
            return -EFAULT;
        }
        let cwd_len = nul_len(&self.cwd);
        if len <= cwd_len {
            return -EINVAL;
        }
        unsafe {
            core::ptr::copy_nonoverlapping(self.cwd.as_ptr(), buffer, cwd_len);
            buffer.add(cwd_len).write(0);
        }
        (cwd_len + 1) as isize
    }

    fn busybox_fallback(&self, path: &[u8]) -> Option<usize> {
        if is_busybox_applet_path(path) {
            self.find(b"/usr/bin/busybox")
                .or_else(|| self.find(b"/bin/busybox"))
        } else {
            None
        }
    }

    fn insert_fixup(&mut self, mut node: usize) {
        while self.color(self.nodes[node].parent) == Color::Red {
            let parent = self.nodes[node].parent.unwrap();
            let grandparent = self.nodes[parent].parent.unwrap();

            if self.nodes[grandparent].left == Some(parent) {
                let uncle = self.nodes[grandparent].right;
                if self.color(uncle) == Color::Red {
                    self.nodes[parent].color = Color::Black;
                    if let Some(uncle) = uncle {
                        self.nodes[uncle].color = Color::Black;
                    }
                    self.nodes[grandparent].color = Color::Red;
                    node = grandparent;
                } else {
                    if self.nodes[parent].right == Some(node) {
                        node = parent;
                        self.rotate_left(node);
                    }
                    let parent = self.nodes[node].parent.unwrap();
                    let grandparent = self.nodes[parent].parent.unwrap();
                    self.nodes[parent].color = Color::Black;
                    self.nodes[grandparent].color = Color::Red;
                    self.rotate_right(grandparent);
                }
            } else {
                let uncle = self.nodes[grandparent].left;
                if self.color(uncle) == Color::Red {
                    self.nodes[parent].color = Color::Black;
                    if let Some(uncle) = uncle {
                        self.nodes[uncle].color = Color::Black;
                    }
                    self.nodes[grandparent].color = Color::Red;
                    node = grandparent;
                } else {
                    if self.nodes[parent].left == Some(node) {
                        node = parent;
                        self.rotate_right(node);
                    }
                    let parent = self.nodes[node].parent.unwrap();
                    let grandparent = self.nodes[parent].parent.unwrap();
                    self.nodes[parent].color = Color::Black;
                    self.nodes[grandparent].color = Color::Red;
                    self.rotate_left(grandparent);
                }
            }
        }

        if let Some(root) = self.root {
            self.nodes[root].color = Color::Black;
        }
    }

    fn rotate_left(&mut self, node: usize) {
        let Some(right) = self.nodes[node].right else {
            return;
        };
        self.nodes[node].right = self.nodes[right].left;
        if let Some(right_left) = self.nodes[right].left {
            self.nodes[right_left].parent = Some(node);
        }

        self.nodes[right].parent = self.nodes[node].parent;
        if let Some(parent) = self.nodes[node].parent {
            if self.nodes[parent].left == Some(node) {
                self.nodes[parent].left = Some(right);
            } else {
                self.nodes[parent].right = Some(right);
            }
        } else {
            self.root = Some(right);
        }

        self.nodes[right].left = Some(node);
        self.nodes[node].parent = Some(right);
    }

    fn rotate_right(&mut self, node: usize) {
        let Some(left) = self.nodes[node].left else {
            return;
        };
        self.nodes[node].left = self.nodes[left].right;
        if let Some(left_right) = self.nodes[left].right {
            self.nodes[left_right].parent = Some(node);
        }

        self.nodes[left].parent = self.nodes[node].parent;
        if let Some(parent) = self.nodes[node].parent {
            if self.nodes[parent].right == Some(node) {
                self.nodes[parent].right = Some(left);
            } else {
                self.nodes[parent].left = Some(left);
            }
        } else {
            self.root = Some(left);
        }

        self.nodes[left].right = Some(node);
        self.nodes[node].parent = Some(left);
    }

    fn color(&self, node: Option<usize>) -> Color {
        node.map(|index| self.nodes[index].color)
            .unwrap_or(Color::Black)
    }
}

static mut VFS: Vfs = Vfs::new();

pub unsafe fn init() {
    unsafe {
        let vfs = vfs_mut();
        vfs.reset();
        let _ = vfs.insert(b"/", NodeKind::Directory, core::ptr::null(), 0);
        let _ = vfs.insert(b"/bin", NodeKind::Directory, core::ptr::null(), 0);
        let _ = vfs.insert(b"/dev", NodeKind::Directory, core::ptr::null(), 0);
        let _ = vfs.insert(b"/dev/tty", NodeKind::CharDevice, core::ptr::null(), 0);
        let _ = vfs.insert(b"/etc", NodeKind::Directory, core::ptr::null(), 0);
        let _ = vfs.insert(b"/tmp", NodeKind::Directory, core::ptr::null(), 0);
        let _ = vfs.insert(b"/usr", NodeKind::Directory, core::ptr::null(), 0);
        let _ = vfs.insert(b"/usr/bin", NodeKind::Directory, core::ptr::null(), 0);
        if let Some(tty) = vfs.find(b"/dev/tty") {
            vfs.fds[0] = FileDescriptor {
                node: Some(tty),
                offset: 0,
            };
            vfs.fds[1] = FileDescriptor {
                node: Some(tty),
                offset: 0,
            };
            vfs.fds[2] = FileDescriptor {
                node: Some(tty),
                offset: 0,
            };
        }
    }
}

#[allow(dead_code)]
pub fn mount_ext4_node(path: &[u8], kind: NodeKind) -> Option<()> {
    unsafe { vfs_mut().insert(path, kind, core::ptr::null(), 0) }
}

#[allow(dead_code)]
pub fn open_user_path(path: *const u8) -> isize {
    open_user_path_with_flags(path, 0)
}

pub fn open_user_path_with_flags(path: *const u8, flags: usize) -> isize {
    let Some(path) = (unsafe { read_user_path(path) }) else {
        return -EFAULT;
    };
    if flags & 0o100 != 0 && unsafe { vfs_ref().find(&path).is_none() } {
        let result = create_regular_path(&path);
        if result < 0 {
            return result;
        }
    }
    unsafe { vfs_mut().open_path(&path) }
}

pub fn openat_user_path(dirfd: isize, path: *const u8, flags: usize) -> isize {
    if unsafe { path_starts_with_slash(path) } || dirfd == AT_FDCWD {
        return open_user_path_with_flags(path, flags);
    }

    let base = match unsafe { vfs_ref().fd_dir_path(dirfd as usize) } {
        Ok(path) => path,
        Err(error) => return error,
    };
    let Some(path) = (unsafe { read_user_path_relative(&base, path) }) else {
        return -EFAULT;
    };
    if flags & 0o100 != 0 && unsafe { vfs_ref().find(&path).is_none() } {
        let result = create_regular_path(&path);
        if result < 0 {
            return result;
        }
    }
    unsafe { vfs_mut().open_path(&path) }
}

pub fn read(fd: usize, buffer: *mut u8, len: usize) -> isize {
    unsafe { vfs_mut().read_fd(fd, buffer, len) }
}

pub fn write(fd: usize, buffer: *const u8, len: usize) -> isize {
    unsafe { vfs_mut().write_fd(fd, buffer, len) }
}

pub fn close(fd: usize) -> isize {
    unsafe { vfs_mut().close_fd(fd) }
}

pub fn dup(fd: usize) -> isize {
    unsafe { vfs_mut().dup_fd(fd, 3) }
}

pub fn dup_min(fd: usize, min_newfd: usize) -> isize {
    unsafe { vfs_mut().dup_fd(fd, min_newfd) }
}

pub fn dup2(oldfd: usize, newfd: usize) -> isize {
    unsafe { vfs_mut().dup2_fd(oldfd, newfd) }
}

pub fn lseek(fd: usize, offset: isize, whence: usize) -> isize {
    unsafe { vfs_mut().lseek_fd(fd, offset, whence) }
}

pub fn fstat(fd: usize, stat: *mut u8) -> isize {
    unsafe { vfs_ref().stat_fd(fd, stat) }
}

pub fn ftruncate(fd: usize, size: usize) -> isize {
    unsafe { vfs_mut().ftruncate_fd(fd, size) }
}

pub fn is_tty(fd: usize) -> bool {
    unsafe { vfs_ref().is_tty_fd(fd) }
}

pub fn poll(fd: usize, events: i16) -> Option<i16> {
    if !unsafe { vfs_ref().is_tty_fd(fd) } {
        return None;
    }
    let mut revents = 0;
    if events & 0x0001 != 0 && crate::console::has_input() {
        revents |= 0x0001;
    }
    if events & 0x0004 != 0 {
        revents |= 0x0004;
    }
    Some(revents)
}

pub fn getdents64(fd: usize, buffer: *mut u8, len: usize) -> isize {
    unsafe { vfs_mut().getdents64_fd(fd, buffer, len) }
}

pub fn stat_user_path(path: *const u8, stat: *mut u8) -> isize {
    let Some(path) = (unsafe { read_user_path(path) }) else {
        return -EFAULT;
    };
    unsafe { vfs_ref().stat_path(&path, stat) }
}

pub fn truncate_user_path(path: *const u8, size: usize) -> isize {
    let Some(path) = (unsafe { read_user_path(path) }) else {
        return -EFAULT;
    };
    unsafe { vfs_mut().truncate_path(&path, size) }
}

pub fn statat_user_path(dirfd: isize, path: *const u8, stat: *mut u8) -> isize {
    if unsafe { path_starts_with_slash(path) } || dirfd == AT_FDCWD {
        return stat_user_path(path, stat);
    }

    let base = match unsafe { vfs_ref().fd_dir_path(dirfd as usize) } {
        Ok(path) => path,
        Err(_) => return stat_user_path(path, stat),
    };
    let Some(path) = (unsafe { read_user_path_relative(&base, path) }) else {
        return -EFAULT;
    };
    unsafe { vfs_ref().stat_path(&path, stat) }
}

pub fn access_user_path(path: *const u8) -> isize {
    let Some(path) = (unsafe { read_user_path(path) }) else {
        return -EFAULT;
    };
    unsafe {
        if vfs_ref().resolve_executable_path(&path).is_some() {
            0
        } else {
            -ENOENT
        }
    }
}

pub fn chdir_user_path(path: *const u8) -> isize {
    let Some(path) = (unsafe { read_user_path(path) }) else {
        return -EFAULT;
    };
    unsafe { vfs_mut().chdir_path(&path) }
}

pub fn mkdir_user_path(path: *const u8) -> isize {
    let Some(path) = (unsafe { read_user_path(path) }) else {
        return -EFAULT;
    };
    create_directory_path(&path)
}

pub fn mkdirat_user_path(dirfd: isize, path: *const u8) -> isize {
    if unsafe { path_starts_with_slash(path) } || dirfd == AT_FDCWD {
        return mkdir_user_path(path);
    }

    let base = match unsafe { vfs_ref().fd_dir_path(dirfd as usize) } {
        Ok(path) => path,
        Err(error) => return error,
    };
    let Some(path) = (unsafe { read_user_path_relative(&base, path) }) else {
        return -EFAULT;
    };
    create_directory_path(&path)
}

pub fn touch_user_path(dirfd: isize, path: *const u8) -> isize {
    let resolved = if unsafe { path_starts_with_slash(path) } || dirfd == AT_FDCWD {
        unsafe { read_user_path(path) }
    } else {
        let base = match unsafe { vfs_ref().fd_dir_path(dirfd as usize) } {
            Ok(path) => path,
            Err(error) => return error,
        };
        unsafe { read_user_path_relative(&base, path) }
    };
    let Some(path) = resolved else {
        return -EFAULT;
    };
    create_regular_path(&path)
}

fn create_directory_path(path: &[u8]) -> isize {
    if unsafe { vfs_ref().find(path).is_some() } {
        return 0;
    }
    match crate::fs::lwext4::create_dir(path) {
        Ok(()) => unsafe { vfs_mut().create_path(path, NodeKind::Directory) },
        Err(error) => error,
    }
}

fn create_regular_path(path: &[u8]) -> isize {
    if unsafe { vfs_ref().find(path).is_some() } {
        return 0;
    }
    match crate::fs::lwext4::create_file(path) {
        Ok(()) => unsafe { vfs_mut().create_path(path, NodeKind::Regular) },
        Err(error) => error,
    }
}

pub fn getcwd(buffer: *mut u8, len: usize) -> isize {
    unsafe { vfs_ref().getcwd(buffer, len) }
}

pub fn exec_path_user(path: *const u8) -> Option<[u8; MAX_PATH]> {
    let path = unsafe { read_user_path(path) }?;
    unsafe {
        let index = vfs_ref().resolve_executable_path(&path)?;
        Some(vfs_ref().nodes[index].path)
    }
}

unsafe fn vfs_mut() -> &'static mut Vfs {
    unsafe { &mut *(&raw mut VFS) }
}

unsafe fn vfs_ref() -> &'static Vfs {
    unsafe { &*(&raw const VFS) }
}

unsafe fn read_user_path(path: *const u8) -> Option<[u8; MAX_PATH]> {
    if path.is_null() {
        return None;
    }

    let first = unsafe { path.read() };

    if first == 0 {
        return None;
    }
    if first != b'/' {
        return unsafe { read_user_path_relative(&vfs_ref().cwd, path) };
    }
    unsafe { normalize_user_path(path, None) }
}

unsafe fn read_user_path_relative(base: &[u8], path: *const u8) -> Option<[u8; MAX_PATH]> {
    if path.is_null() {
        return None;
    }
    if unsafe { path_starts_with_slash(path) } {
        return unsafe { normalize_user_path(path, None) };
    }

    unsafe { normalize_user_path(path, Some(base)) }
}

unsafe fn normalize_user_path(path: *const u8, base: Option<&[u8]>) -> Option<[u8; MAX_PATH]> {
    let mut buffer = [0u8; MAX_PATH];
    let mut output_index = 0usize;

    if let Some(base) = base {
        let base_len = nul_len(base);
        if base_len == 0 {
            return None;
        }
        for byte in &base[..base_len] {
            if output_index >= MAX_PATH - 1 {
                return None;
            }
            buffer[output_index] = *byte;
            output_index += 1;
        }
    } else {
        buffer[output_index] = b'/';
        output_index += 1;
    }

    let mut input_index = 0;
    loop {
        while unsafe { path.add(input_index).read() } == b'/' {
            input_index += 1;
        }

        let component_start = input_index;
        while {
            let byte = unsafe { path.add(input_index).read() };
            byte != 0 && byte != b'/'
        } {
            input_index += 1;
        }
        let component_len = input_index - component_start;

        if component_len == 0 {
            if output_index == 0 {
                buffer[0] = b'/';
            }
            return Some(buffer);
        }

        if component_len == 1 && unsafe { path.add(component_start).read() } == b'.' {
            continue;
        }

        if component_len == 2
            && unsafe { path.add(component_start).read() } == b'.'
            && unsafe { path.add(component_start + 1).read() } == b'.'
        {
            pop_path_component(&mut buffer, &mut output_index);
            continue;
        }

        if output_index == 0 {
            buffer[output_index] = b'/';
            output_index += 1;
        }
        if !(output_index == 1 && buffer[0] == b'/') {
            if output_index >= MAX_PATH - 1 {
                return None;
            }
            buffer[output_index] = b'/';
            output_index += 1;
        }
        if output_index + component_len >= MAX_PATH {
            return None;
        }
        for index in 0..component_len {
            buffer[output_index + index] = unsafe { path.add(component_start + index).read() };
        }
        output_index += component_len;
    }
}

fn pop_path_component(buffer: &mut [u8; MAX_PATH], output_index: &mut usize) {
    if *output_index <= 1 {
        buffer[0] = b'/';
        for byte in &mut buffer[1..] {
            *byte = 0;
        }
        *output_index = 1;
        return;
    }

    let mut index = *output_index;
    while index > 1 && buffer[index - 1] == b'/' {
        index -= 1;
    }
    while index > 1 && buffer[index - 1] != b'/' {
        index -= 1;
    }
    if index <= 1 {
        buffer[0] = b'/';
        index = 1;
    } else {
        index -= 1;
    }
    for byte in &mut buffer[index..*output_index] {
        *byte = 0;
    }
    *output_index = index;
}

unsafe fn path_starts_with_slash(path: *const u8) -> bool {
    if path.is_null() {
        return false;
    }
    unsafe { path.read() == b'/' }
}

fn compare_path(left: &[u8], right: &[u8]) -> core::cmp::Ordering {
    let mut index = 0;
    loop {
        let left_byte = byte_at(left, index);
        let right_byte = byte_at(right, index);
        match left_byte.cmp(&right_byte) {
            core::cmp::Ordering::Equal => {
                if left_byte == 0 {
                    return core::cmp::Ordering::Equal;
                }
            }
            ordering => return ordering,
        }
        index += 1;
    }
}

fn byte_at(path: &[u8], index: usize) -> u8 {
    path.get(index).copied().unwrap_or(0)
}

fn is_busybox_applet_path(path: &[u8]) -> bool {
    let path_len = nul_len(path);
    if path_len == 0 {
        return false;
    }

    let name = if path_len > b"/bin/".len() && &path[..b"/bin/".len()] == b"/bin/" {
        &path[b"/bin/".len()..path_len]
    } else if path_len > b"/usr/bin/".len() && &path[..b"/usr/bin/".len()] == b"/usr/bin/" {
        &path[b"/usr/bin/".len()..path_len]
    } else {
        return false;
    };

    !name.is_empty() && !name.contains(&b'/')
}

fn align_up(value: usize, align: usize) -> usize {
    (value + align - 1) & !(align - 1)
}

fn dirent_type(kind: NodeKind) -> u8 {
    match kind {
        NodeKind::Directory => 4,
        NodeKind::Regular => 8,
        NodeKind::CharDevice => 2,
    }
}

fn write_dirent(
    buffer: *mut u8,
    buffer_len: usize,
    written: &mut usize,
    ino: u64,
    kind: NodeKind,
    name: &[u8],
) -> bool {
    let reclen = align_up(19 + name.len() + 1, 8);
    if reclen > u16::MAX as usize || *written + reclen > buffer_len {
        return false;
    }

    unsafe {
        let entry = buffer.add(*written);
        (entry as *mut u64).write(ino);
        (entry.add(8) as *mut i64).write(ino as i64);
        (entry.add(16) as *mut u16).write(reclen as u16);
        entry.add(18).write(dirent_type(kind));
        core::ptr::copy_nonoverlapping(name.as_ptr(), entry.add(19), name.len());
        entry.add(19 + name.len()).write(0);
        if reclen > 20 + name.len() {
            core::ptr::write_bytes(entry.add(20 + name.len()), 0, reclen - 20 - name.len());
        }
    }

    *written += reclen;
    true
}

fn child_name<'a>(parent: &[u8], child: &'a [u8]) -> Option<&'a [u8]> {
    if compare_path(parent, child).is_eq() {
        return None;
    }
    let parent_len = nul_len(parent);
    let child_len = nul_len(child);
    if parent_len == 1 && parent[0] == b'/' {
        let name = &child[1..child_len];
        if !name.is_empty() && !name.contains(&b'/') {
            return Some(name);
        }
        return None;
    }
    if child_len <= parent_len + 1
        || &child[..parent_len] != &parent[..parent_len]
        || child[parent_len] != b'/'
    {
        return None;
    }
    let name = &child[parent_len + 1..child_len];
    if !name.is_empty() && !name.contains(&b'/') {
        Some(name)
    } else {
        None
    }
}

fn nul_len(path: &[u8]) -> usize {
    path.iter()
        .position(|byte| *byte == 0)
        .unwrap_or(path.len())
}

fn write_stat(stat: *mut u8, node: VfsNode) -> isize {
    unsafe {
        core::ptr::write_bytes(stat, 0, 144);
        let mode = match node.kind {
            NodeKind::Directory => S_IFDIR | 0o755,
            NodeKind::Regular => S_IFREG | 0o644,
            NodeKind::CharDevice => S_IFCHR | 0o600,
        };
        (stat.add(24) as *mut u32).write(mode);
        (stat.add(48) as *mut u64).write(node.len as u64);
        (stat.add(56) as *mut u64).write(4096);
        (stat.add(64) as *mut u64).write(node.len.div_ceil(512) as u64);
    }
    0
}