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// 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 superblock structure.
use anyhow::Result;
use zerocopy::AsBytes;
use zerocopy_derive::FromBytes;
use zerocopy_derive::FromZeroes;
/// The ext2 superblock.
///
/// The field names are based on [the specification](https://www.nongnu.org/ext2-doc/ext2.html#superblock).
/// Note that this struct only holds the fields at the beginning of the superblock. All fields after
/// the fields supported by this structure are filled with zeros.
#[repr(C)]
#[derive(Default, Debug, Copy, Clone, FromZeroes, FromBytes, AsBytes)]
pub(crate) struct SuperBlock {
inodes_count: u32,
blocks_count: u32,
_r_blocks_count: u32,
free_blocks_count: u32,
free_inodes_count: u32,
_first_data_block: u32,
log_block_size: u32,
log_frag_size: u32,
blocks_per_group: u32,
frags_per_group: u32,
inodes_per_group: u32,
mtime: u32,
wtime: u32,
_mnt_count: u16,
_max_mnt_count: u16,
magic: u16,
state: u16,
errors: u16,
_minor_rev_level: u16,
_lastcheck: u32,
_checkinterval: u32,
_creator_os: u32,
rev_level: u32,
_def_resuid: u16,
_def_resgid: u16,
first_ino: u32,
inode_size: u16,
block_group_nr: u16,
_feature_compat: u32,
feature_incompat: u32,
_feature_ro_compat: u32,
uuid: [u8; 16],
// Add more fields if needed.
}
impl SuperBlock {
pub fn new() -> Result<Self> {
const EXT2_MAGIC_NUMBER: u16 = 0xEF53;
// TODO(b/329359333): Support more than 1 groups for larger data.
let block_group_nr = 1u16;
let blocks_per_group = 1024;
let inodes_per_group = 1024;
let log_block_size = 2; // (1024 << log_block_size) = 4K bytes
let now = std::time::SystemTime::now()
.duration_since(std::time::UNIX_EPOCH)?
.as_secs() as u32;
let uuid = uuid::Uuid::new_v4().into_bytes();
let inodes_count = inodes_per_group * block_group_nr as u32;
let blocks_count = blocks_per_group * block_group_nr as u32;
// Reserve 10 inodes. Usually inode 11 is used for the lost+found directory.
// <https://docs.kernel.org/filesystems/ext4/special_inodes.html>.
let first_ino = 11;
// TODO(b/329359333): Replace this with `std::mem::size_of()` once Inode struct is
// defined.
// TODO(b/333988434): Support larger inode size for extended attributes. Note that
// COMPAT_RESIZE_INODE will also be required.
let inode_size = 128;
Ok(Self {
inodes_count,
blocks_count,
free_blocks_count: blocks_count, // All blocks are free
free_inodes_count: inodes_count, // All inodes are free
log_block_size,
log_frag_size: log_block_size,
blocks_per_group,
frags_per_group: blocks_per_group,
inodes_per_group,
mtime: now,
wtime: now,
magic: EXT2_MAGIC_NUMBER,
state: 1, // clean
errors: 1, // continue on errors
rev_level: 1,
first_ino,
inode_size,
block_group_nr,
feature_incompat: 0x2, // Directory entries contain a type field
uuid,
..Default::default()
})
}
pub fn disk_size(&self) -> u64 {
let block_size = 1024 << self.log_block_size;
(block_size * self.blocks_count) as u64
}
}
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