ext2/src/inode.rs

// Copyright 2024 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

//! Defines the inode structure.

use std::mem::MaybeUninit;
use std::os::unix::fs::MetadataExt;

use anyhow::bail;
use anyhow::Result;
use enumn::N;
use zerocopy::AsBytes;
use zerocopy_derive::FromBytes;
use zerocopy_derive::FromZeroes;

use crate::arena::Arena;
use crate::arena::BlockId;
use crate::blockgroup::GroupMetaData;
use crate::xattr::InlineXattrs;

/// Types of inodes.
#[derive(Debug, PartialEq, Eq, Clone, Copy, N)]
pub enum InodeType {
    Fifo = 0x1,
    Char = 0x2,
    Directory = 0x4,
    Block = 0x6,
    Regular = 0x8,
    Symlink = 0xa,
    Socket = 0xc,
}

impl InodeType {
    /// Converts to a file type for directory entry.
    /// The value is defined in "Table 4.2. Defined Inode File Type Values" in the spec.
    pub fn into_dir_entry_file_type(self) -> u8 {
        match self {
            InodeType::Regular => 1,
            InodeType::Directory => 2,
            InodeType::Char => 3,
            InodeType::Block => 4,
            InodeType::Fifo => 5,
            InodeType::Socket => 6,
            InodeType::Symlink => 7,
        }
    }
}

// Represents an inode number.
// This is 1-indexed.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub(crate) struct InodeNum(pub u32);

impl InodeNum {
    pub fn new(inode: u32) -> Result<Self> {
        if inode == 0 {
            bail!("inode number is 1-indexed");
        }
        Ok(Self(inode))
    }

    // Returns index in the inode table.
    pub fn to_table_index(self) -> usize {
        // (num - 1) because inode is 1-indexed.
        self.0 as usize - 1
    }
}

impl From<InodeNum> for u32 {
    fn from(inode: InodeNum) -> Self {
        inode.0
    }
}

impl From<InodeNum> for usize {
    fn from(inode: InodeNum) -> Self {
        inode.0 as usize
    }
}

/// Size of the `block` field in Inode.
const INODE_BLOCK_LEN: usize = 60;
/// Represents 60-byte region for block in Inode.
/// This region is used for various ways depending on the file type.
/// For regular files and directories, it's used for storing 32-bit indices of blocks.
///
/// This is a wrapper of `[u8; 60]` to implement `Default` manually.
#[repr(C)]
#[derive(Debug, Copy, Clone, FromZeroes, FromBytes, AsBytes)]
pub(crate) struct InodeBlock(pub [u8; INODE_BLOCK_LEN]);

impl Default for InodeBlock {
    fn default() -> Self {
        Self([0; INODE_BLOCK_LEN])
    }
}

impl InodeBlock {
    // Each inode contains 12 direct pointers (0-11), one singly indirect pointer (12), one
    // doubly indirect block pointer (13), and one triply indirect pointer (14).
    pub const NUM_DIRECT_BLOCKS: usize = 12;
    const INDIRECT_BLOCK_TABLE_ID: usize = Self::NUM_DIRECT_BLOCKS;
    const DOUBLE_INDIRECT_BLOCK_TABLE_ID: usize = 13;

    /// Set a block id at the given index.
    pub fn set_block_id(&mut self, index: usize, block_id: &BlockId) -> Result<()> {
        let offset = index * std::mem::size_of::<BlockId>();
        let bytes = block_id.as_bytes();
        if self.0.len() < offset + bytes.len() {
            bail!("index out of bounds when setting block_id to InodeBlock: index={index}, block_id: {:?}", block_id);
        }
        self.0[offset..offset + bytes.len()].copy_from_slice(bytes);
        Ok(())
    }

    /// Set an array of direct block IDs.
    pub fn set_direct_blocks_from(
        &mut self,
        start_idx: usize,
        block_ids: &[BlockId],
    ) -> Result<()> {
        let bytes = block_ids.as_bytes();
        if bytes.len() + start_idx * 4 > self.0.len() {
            bail!(
                "length of direct blocks is {} bytes, but it must not exceed {}",
                bytes.len(),
                self.0.len()
            );
        }
        self.0[start_idx * 4..(start_idx * 4 + bytes.len())].copy_from_slice(bytes);
        Ok(())
    }

    /// Set an array of direct block IDs.
    pub fn set_direct_blocks(&mut self, block_ids: &[BlockId]) -> Result<()> {
        self.set_direct_blocks_from(0, block_ids)
    }

    /// Set a block id to be used as the indirect block table.
    pub fn set_indirect_block_table(&mut self, block_id: &BlockId) -> Result<()> {
        self.set_block_id(Self::INDIRECT_BLOCK_TABLE_ID, block_id)
    }

    /// Set a block id to be used as the double indirect block table.
    pub fn set_double_indirect_block_table(&mut self, block_id: &BlockId) -> Result<()> {
        self.set_block_id(Self::DOUBLE_INDIRECT_BLOCK_TABLE_ID, block_id)
    }

    /// Returns the max length of symbolic links that can be stored in the inode data.
    /// This length contains the trailing `\0`.
    pub const fn max_inline_symlink_len() -> usize {
        INODE_BLOCK_LEN
    }

    /// Stores a given string as an inlined symbolic link data.
    pub fn set_inline_symlink(&mut self, symlink: &str) -> Result<()> {
        let bytes = symlink.as_bytes();
        if bytes.len() >= Self::max_inline_symlink_len() {
            bail!(
                "symlink '{symlink}' exceeds or equals tomax length: {} >= {}",
                bytes.len(),
                Self::max_inline_symlink_len()
            );
        }
        self.0[..bytes.len()].copy_from_slice(bytes);
        Ok(())
    }
}

/// The ext2 inode.
///
/// The field names are based on [the specification](https://www.nongnu.org/ext2-doc/ext2.html#inode-table).
#[repr(C)]
#[derive(Debug, Copy, Clone, FromZeroes, FromBytes, AsBytes)]
pub(crate) struct Inode {
    mode: u16,
    uid: u16,
    pub size: u32,
    atime: u32,
    ctime: u32,
    mtime: u32,
    _dtime: u32,
    gid: u16,
    pub links_count: u16,
    pub blocks: InodeBlocksCount,
    _flags: u32,
    _osd1: u32,
    pub block: InodeBlock,
    _generation: u32,
    _file_acl: u32,
    _dir_acl: u32,
    _faddr: u32,
    _fragment_num: u8,
    _fragment_size: u8,
    _reserved1: u16,
    uid_high: u16,
    gid_high: u16,
    _reserved2: u32, // 128-th byte

    // We don't use any inode metadata region beyond the basic 128 bytes.
    // However set `extra_size` to the minimum value to let Linux kernel know that there are
    // inline extended attribute data. The minimum possible is 4 bytes, so define extra_size
    // and add the next padding.
    pub extra_size: u16,
    _paddings: u16, // padding for 32-bit alignment
}

impl Default for Inode {
    fn default() -> Self {
        // SAFETY: zero-filled value is a valid value.
        let mut r: Self = unsafe { MaybeUninit::zeroed().assume_init() };
        // Set extra size to 4 for `extra_size` and `paddings` fields.
        r.extra_size = 4;
        r
    }
}

/// Used in `Inode` to represent how many 512-byte blocks are used by a file.
///
/// The block size '512' byte is fixed and not related to the actual block size of the file system.
/// For more details, see notes for `i_blocks_lo` in the specification.
#[repr(C)]
#[derive(Default, Debug, Copy, Clone, FromZeroes, FromBytes, AsBytes)]
pub struct InodeBlocksCount(u32);

impl InodeBlocksCount {
    const INODE_BLOCKS_SIZE: u32 = 512;

    pub fn from_bytes_len(len: u32) -> Self {
        Self(len / Self::INODE_BLOCKS_SIZE)
    }

    pub fn add(&mut self, v: u32) {
        self.0 += v / Self::INODE_BLOCKS_SIZE;
    }
}

impl Inode {
    /// Size of the inode record in bytes.
    ///
    /// From ext2 revision 1, inode size larger than 128 bytes is supported.
    /// We use 256 byte here, which is the default value for ext4.
    ///
    /// Note that inode "record" size can be larger that inode "structure" size.
    /// The gap between the end of the inode structure and the end of the inode record can be used
    /// to store extended attributes.
    pub const INODE_RECORD_SIZE: usize = 256;

    /// Size of the region that inline extended attributes can be written.
    pub const XATTR_AREA_SIZE: usize = Inode::INODE_RECORD_SIZE - std::mem::size_of::<Inode>();

    pub fn new<'a>(
        arena: &'a Arena<'a>,
        group: &mut GroupMetaData,
        inode_num: InodeNum,
        typ: InodeType,
        size: u32,
        xattr: Option<InlineXattrs>,
    ) -> Result<&'a mut Self> {
        const EXT2_S_IRUSR: u16 = 0x0100; // user read
        const EXT2_S_IXUSR: u16 = 0x0040; // user execute
        const EXT2_S_IRGRP: u16 = 0x0020; // group read
        const EXT2_S_IXGRP: u16 = 0x0008; // group execute
        const EXT2_S_IROTH: u16 = 0x0004; // others read
        const EXT2_S_IXOTH: u16 = 0x0001; // others execute

        let inode_offset = inode_num.to_table_index() * Inode::INODE_RECORD_SIZE;
        let inode =
            arena.allocate::<Inode>(BlockId::from(group.group_desc.inode_table), inode_offset)?;

        // Give read and execute permissions
        let mode = ((typ as u16) << 12)
            | EXT2_S_IRUSR
            | EXT2_S_IXUSR
            | EXT2_S_IRGRP
            | EXT2_S_IXGRP
            | EXT2_S_IROTH
            | EXT2_S_IXOTH;

        let now = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)?
            .as_secs() as u32;

        // SAFETY: geteuid never fail.
        let uid = unsafe { libc::geteuid() };
        let uid_high = (uid >> 16) as u16;
        let uid_low = uid as u16;
        // SAFETY: getegid never fail.
        let gid = unsafe { libc::getegid() };
        let gid_high = (gid >> 16) as u16;
        let gid_low = gid as u16;

        *inode = Self {
            mode,
            size,
            atime: now,
            ctime: now,
            mtime: now,
            uid: uid_low,
            gid: gid_low,
            uid_high,
            gid_high,
            ..Default::default()
        };
        if let Some(xattr) = xattr {
            Self::add_xattr(arena, group, inode, inode_offset, xattr)?;
        }

        Ok(inode)
    }

    pub fn from_metadata<'a>(
        arena: &'a Arena<'a>,
        group: &mut GroupMetaData,
        inode_num: InodeNum,
        m: &std::fs::Metadata,
        size: u32,
        links_count: u16,
        blocks: InodeBlocksCount,
        block: InodeBlock,
        xattr: Option<InlineXattrs>,
    ) -> Result<&'a mut Self> {
        let inodes_per_group = group.inode_bitmap.len();
        // (inode_num - 1) because inode is 1-indexed.
        let inode_offset =
            ((usize::from(inode_num) - 1) % inodes_per_group) * Inode::INODE_RECORD_SIZE;
        let inode =
            arena.allocate::<Inode>(BlockId::from(group.group_desc.inode_table), inode_offset)?;

        let mode = m.mode() as u16;

        let uid = m.uid();
        let uid_high = (uid >> 16) as u16;
        let uid_low: u16 = uid as u16;
        let gid = m.gid();
        let gid_high = (gid >> 16) as u16;
        let gid_low: u16 = gid as u16;

        let atime = m.atime() as u32;
        let ctime = m.ctime() as u32;
        let mtime = m.mtime() as u32;

        *inode = Inode {
            mode,
            uid: uid_low,
            gid: gid_low,
            size,
            atime,
            ctime,
            mtime,
            links_count,
            blocks,
            block,
            uid_high,
            gid_high,
            ..Default::default()
        };

        if let Some(xattr) = xattr {
            Self::add_xattr(arena, group, inode, inode_offset, xattr)?;
        }

        Ok(inode)
    }

    fn add_xattr<'a>(
        arena: &'a Arena<'a>,
        group: &mut GroupMetaData,
        inode: &mut Inode,
        inode_offset: usize,
        xattr: InlineXattrs,
    ) -> Result<()> {
        let xattr_region = arena.allocate::<[u8; Inode::XATTR_AREA_SIZE]>(
            BlockId::from(group.group_desc.inode_table),
            inode_offset + std::mem::size_of::<Inode>(),
        )?;

        if !xattr.entry_table.is_empty() {
            // Linux and debugfs uses extra_size to check if inline xattr is stored so we need to
            // set a positive value here. 4 (= sizeof(extra_size) + sizeof(_paddings))
            // is the smallest value.
            inode.extra_size = 4;
            let InlineXattrs {
                entry_table,
                values,
            } = xattr;

            if entry_table.len() + values.len() > Inode::XATTR_AREA_SIZE {
                bail!("xattr size is too large for inline store: entry_table.len={}, values.len={}, inline region size={}",
                        entry_table.len(), values.len(), Inode::XATTR_AREA_SIZE);
            }
            // `entry_table` should be aligned to the beginning of the region.
            xattr_region[..entry_table.len()].copy_from_slice(&entry_table);
            xattr_region[Inode::XATTR_AREA_SIZE - values.len()..].copy_from_slice(&values);
        }
        Ok(())
    }

    pub fn update_metadata(&mut self, m: &std::fs::Metadata) {
        self.mode = m.mode() as u16;

        let uid: u32 = m.uid();
        self.uid_high = (uid >> 16) as u16;
        self.uid = uid as u16;
        let gid = m.gid();
        self.gid_high = (gid >> 16) as u16;
        self.gid = gid as u16;

        self.atime = m.atime() as u32;
        self.ctime = m.ctime() as u32;
        self.mtime = m.mtime() as u32;
    }

    pub fn typ(&self) -> Option<InodeType> {
        InodeType::n((self.mode >> 12) as u8)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_inode_size() {
        assert_eq!(std::mem::offset_of!(Inode, extra_size), 128);
        // Check that no implicit paddings is inserted after the padding field.
        assert_eq!(
            std::mem::offset_of!(Inode, _paddings) + std::mem::size_of::<u16>(),
            std::mem::size_of::<Inode>()
        );

        assert!(128 < std::mem::size_of::<Inode>());
        assert!(std::mem::size_of::<Inode>() <= Inode::INODE_RECORD_SIZE);
    }
}