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refactor(userspace): split syscall/fat16/ext4 by concern; trim comments

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This commit is contained in:
Gabriel Kaszewski
2026-10-27 13:21:53 +01:00
parent 99273db6d3
commit b4390b7b6d
25 changed files with 1283 additions and 1229 deletions
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6
crates/servers/storage-server/src/fs/ext4/dir.rs
View File

@@ -96,9 +96,7 @@ pub fn add_entry<B: BlockDevice>(
let free_space = rec_len - actual_size;
if free_space >= new_rec_needed {
if entry_inode != 0 {
// Shrink this entry to its actual size
write_u16(&mut block_buf, pos + 4, actual_size as u16);
// Write new entry after it
let new_pos = pos + actual_size;
write_u32(&mut block_buf, new_pos, child_inode);
write_u16(&mut block_buf, new_pos + 4, free_space as u16);
@@ -106,9 +104,7 @@ pub fn add_entry<B: BlockDevice>(
block_buf[new_pos + 7] = file_type;
block_buf[new_pos + 8..new_pos + 8 + name.len()].copy_from_slice(name);
} else {
// Reuse deleted entry
write_u32(&mut block_buf, pos, child_inode);
// Keep rec_len as is
block_buf[pos + 6] = name.len() as u8;
block_buf[pos + 7] = file_type;
block_buf[pos + 8..pos + 8 + name.len()].copy_from_slice(name);
@@ -160,11 +156,9 @@ pub fn remove_entry<B: BlockDevice>(
if entry_inode != 0 && name_len == name.len() {
if &block_buf[pos + 8..pos + 8 + name_len] == name {
if let Some(pp) = prev_pos {
// Merge with previous entry
let prev_rec = read_u16(&block_buf, pp + 4) as usize;
write_u16(&mut block_buf, pp + 4, (prev_rec + rec_len) as u16);
} else {
// First entry — zero the inode
write_u32(&mut block_buf, pos, 0);
}
write_block(device, phys, spb, &block_buf);

99
crates/servers/storage-server/src/fs/ext4/extent.rs Normal file
View File

@@ -0,0 +1,99 @@
//! Extent tree (depth 0 only): block mapping and allocation.
use super::io::{self, read_u16};
use super::{Ext4, Extent, Inode, EXTENT_MAGIC};
use port_block_device::BlockDevice;
impl<B: BlockDevice> Ext4<B> {
pub(super) fn read_extents(&self, inode: &Inode) -> Option<Extent> {
if !inode.uses_extents() { return None; }
let hdr = &inode.block_data;
let magic = read_u16(hdr, 0);
if magic != EXTENT_MAGIC { return None; }
let entries = read_u16(hdr, 2);
let depth = read_u16(hdr, 6);
if depth != 0 || entries == 0 { return None; }
Some(Extent::parse(&hdr[12..24]))
}
pub(super) fn map_logical_block(&mut self, inode: &Inode, logical_block: u32) -> Option<u64> {
if !inode.uses_extents() { return None; }
let hdr = &inode.block_data;
let magic = read_u16(hdr, 0);
if magic != EXTENT_MAGIC { return None; }
let entries = read_u16(hdr, 2);
let depth = read_u16(hdr, 6);
if depth != 0 {
return None;
}
for i in 0..entries as usize {
let off = 12 + i * 12;
if off + 12 > hdr.len() { break; }
let ext = Extent::parse(&hdr[off..off + 12]);
if logical_block >= ext.logical_block
&& logical_block < ext.logical_block + ext.length as u32
{
return Some(ext.physical_block + (logical_block - ext.logical_block) as u64);
}
}
None
}
pub(super) fn append_extent(block_data: &mut [u8], logical_block: u32, physical_block: u64, length: u16) -> bool {
let magic = read_u16(block_data, 0);
if magic != EXTENT_MAGIC { return false; }
let entries = read_u16(block_data, 2);
let max = read_u16(block_data, 4);
if entries > 0 {
let last_off = 12 + (entries as usize - 1) * 12;
let last = Extent::parse(&block_data[last_off..last_off + 12]);
if last.physical_block + last.length as u64 == physical_block
&& last.logical_block + last.length as u32 == logical_block
{
let new_len = last.length + length;
io::write_u16(block_data, last_off + 4, new_len);
return true;
}
}
if entries >= max { return false; }
let off = 12 + entries as usize * 12;
if off + 12 > block_data.len() { return false; }
io::write_u32(block_data, off, logical_block);
io::write_u16(block_data, off + 4, length);
io::write_u16(block_data, off + 6, (physical_block >> 32) as u16);
io::write_u32(block_data, off + 8, physical_block as u32);
io::write_u16(block_data, 2, entries + 1);
true
}
pub(super) fn count_extent_blocks(block_data: &[u8; 60]) -> u32 {
let magic = read_u16(block_data, 0);
if magic != EXTENT_MAGIC { return 0; }
let entries = read_u16(block_data, 2);
let mut total = 0u32;
for i in 0..entries as usize {
let off = 12 + i * 12;
if off + 12 > block_data.len() { break; }
total += read_u16(block_data, off + 4) as u32;
}
total
}
pub(super) fn free_all_blocks(&mut self, inode: &Inode) {
if !inode.uses_extents() { return; }
let hdr = &inode.block_data;
let magic = read_u16(hdr, 0);
if magic != EXTENT_MAGIC { return; }
let entries = read_u16(hdr, 2);
for i in 0..entries as usize {
let off = 12 + i * 12;
if off + 12 > hdr.len() { break; }
let ext = Extent::parse(&hdr[off..off + 12]);
for b in 0..ext.length as u32 {
self.free_block(ext.physical_block as u32 + b);
}
}
}
}

136
crates/servers/storage-server/src/fs/ext4/inode.rs Normal file
View File

@@ -0,0 +1,136 @@
//! Inode and extent records, and inode table access.
use super::bgd::BlockGroupDescriptor;
use super::io::{self, read_block, read_u16, read_u32};
use super::{Ext4, EXTENT_MAGIC};
use port_block_device::BlockDevice;
pub struct Inode {
pub mode: u16,
pub size: u64,
pub flags: u32,
pub links_count: u16,
pub blocks_count: u32,
pub block_data: [u8; 60],
}
impl Inode {
pub fn is_dir(&self) -> bool { self.mode & 0xF000 == 0x4000 }
pub fn is_file(&self) -> bool { self.mode & 0xF000 == 0x8000 }
pub fn uses_extents(&self) -> bool { self.flags & 0x80000 != 0 }
}
#[derive(Clone, Copy)]
pub struct Extent {
pub logical_block: u32,
pub length: u16,
pub physical_block: u64,
}
impl Extent {
pub fn parse(data: &[u8]) -> Self {
let start_hi = read_u16(data, 6) as u64;
let start_lo = read_u32(data, 8) as u64;
Self {
logical_block: read_u32(data, 0),
length: read_u16(data, 4),
physical_block: (start_hi << 32) | start_lo,
}
}
}
impl<B: BlockDevice> Ext4<B> {
pub(super) fn read_inode(&mut self, inode_num: u32) -> Option<Inode> {
let bgd = BlockGroupDescriptor::read(
&mut self.device, self.gdt_block,
self.sb.inode_block_group(inode_num),
self.sb.sectors_per_block(),
)?;
let index = self.sb.inode_index_in_group(inode_num);
let inode_offset = (index as usize) * (self.sb.inode_size as usize);
let block_offset = inode_offset / self.sb.block_size;
let offset_in_block = inode_offset % self.sb.block_size;
let mut block_buf = [0u8; 4096];
read_block(
&mut self.device,
(bgd.inode_table + block_offset as u32) as u64,
self.sb.sectors_per_block(),
&mut block_buf,
);
let d = &block_buf[offset_in_block..];
if d.len() < 128 { return None; }
let size_lo = read_u32(d, 0x04) as u64;
let size_hi = read_u32(d, 0x6C) as u64;
let size = size_lo | (size_hi << 32);
let mut block_data = [0u8; 60];
block_data.copy_from_slice(&d[0x28..0x64]);
Some(Inode {
mode: read_u16(d, 0x00),
size,
flags: read_u32(d, 0x20),
links_count: read_u16(d, 0x1A),
blocks_count: read_u32(d, 0x1C),
block_data,
})
}
pub(super) fn write_inode(&mut self, inode_num: u32, inode: &Inode) -> bool {
let bgd = match BlockGroupDescriptor::read(
&mut self.device, self.gdt_block,
self.sb.inode_block_group(inode_num),
self.sb.sectors_per_block(),
) {
Some(b) => b,
None => return false,
};
let index = self.sb.inode_index_in_group(inode_num);
let inode_offset = (index as usize) * (self.sb.inode_size as usize);
let block_offset = inode_offset / self.sb.block_size;
let offset_in_block = inode_offset % self.sb.block_size;
let mut block_buf = [0u8; 4096];
let block_num = (bgd.inode_table + block_offset as u32) as u64;
read_block(&mut self.device, block_num, self.sb.sectors_per_block(), &mut block_buf);
let d = &mut block_buf[offset_in_block..];
io::write_u16(d, 0x00, inode.mode);
io::write_u32(d, 0x04, inode.size as u32);
io::write_u16(d, 0x1A, inode.links_count);
io::write_u32(d, 0x1C, inode.blocks_count);
io::write_u32(d, 0x20, inode.flags);
d[0x28..0x64].copy_from_slice(&inode.block_data);
io::write_u32(d, 0x6C, (inode.size >> 32) as u32);
io::write_block(&mut self.device, block_num, self.sb.sectors_per_block(), &block_buf)
}
pub fn init_empty_inode(mode: u16) -> Inode {
let mut block_data = [0u8; 60];
io::write_u16(&mut block_data, 0, EXTENT_MAGIC);
io::write_u16(&mut block_data, 2, 0); // entries = 0
io::write_u16(&mut block_data, 4, 4); // max = 4
io::write_u16(&mut block_data, 6, 0); // depth = 0
Inode {
mode,
size: 0,
flags: 0x80000,
links_count: 1,
blocks_count: 0,
block_data,
}
}
pub fn read_inode_pub(&mut self, inode_num: u32) -> Option<Inode> {
self.read_inode(inode_num)
}
pub fn write_inode_pub(&mut self, inode_num: u32, inode: &Inode) -> bool {
self.write_inode(inode_num, inode)
}
}

298
crates/servers/storage-server/src/fs/ext4/mod.rs
View File

@@ -3,50 +3,21 @@ pub mod superblock;
pub mod bgd;
pub mod bitmap;
pub mod dir;
mod extent;
mod inode;
mod path;
use port_block_device::BlockDevice;
use crate::filesystem::{DirEntry, FileHandle, FileName, FileSystem};
use io::{read_block, read_u32, read_u16};
use io::read_block;
use superblock::Superblock;
use bgd::BlockGroupDescriptor;
const ROOT_INODE: u32 = 2;
const MAX_OPEN_FILES: usize = 8;
const EXTENT_MAGIC: u16 = 0xF30A;
pub struct Inode {
pub mode: u16,
pub size: u64,
pub flags: u32,
pub links_count: u16,
pub blocks_count: u32,
pub block_data: [u8; 60],
}
impl Inode {
pub fn is_dir(&self) -> bool { self.mode & 0xF000 == 0x4000 }
pub fn is_file(&self) -> bool { self.mode & 0xF000 == 0x8000 }
pub fn uses_extents(&self) -> bool { self.flags & 0x80000 != 0 }
}
#[derive(Clone, Copy)]
pub struct Extent {
pub logical_block: u32,
pub length: u16,
pub physical_block: u64,
}
impl Extent {
pub fn parse(data: &[u8]) -> Self {
let start_hi = read_u16(data, 6) as u64;
let start_lo = read_u32(data, 8) as u64;
Self {
logical_block: read_u32(data, 0),
length: read_u16(data, 4),
physical_block: (start_hi << 32) | start_lo,
}
}
}
pub use inode::{Extent, Inode};
#[derive(Clone, Copy)]
struct OpenFile {
@@ -80,265 +51,6 @@ impl<B: BlockDevice> Ext4<B> {
open_files: [const { None }; MAX_OPEN_FILES],
})
}
fn read_inode(&mut self, inode_num: u32) -> Option<Inode> {
let bgd = BlockGroupDescriptor::read(
&mut self.device, self.gdt_block,
self.sb.inode_block_group(inode_num),
self.sb.sectors_per_block(),
)?;
let index = self.sb.inode_index_in_group(inode_num);
let inode_offset = (index as usize) * (self.sb.inode_size as usize);
let block_offset = inode_offset / self.sb.block_size;
let offset_in_block = inode_offset % self.sb.block_size;
let mut block_buf = [0u8; 4096];
read_block(
&mut self.device,
(bgd.inode_table + block_offset as u32) as u64,
self.sb.sectors_per_block(),
&mut block_buf,
);
let d = &block_buf[offset_in_block..];
if d.len() < 128 { return None; }
let size_lo = read_u32(d, 0x04) as u64;
let size_hi = read_u32(d, 0x6C) as u64;
let size = size_lo | (size_hi << 32);
let mut block_data = [0u8; 60];
block_data.copy_from_slice(&d[0x28..0x64]);
Some(Inode {
mode: read_u16(d, 0x00),
size,
flags: read_u32(d, 0x20),
links_count: read_u16(d, 0x1A),
blocks_count: read_u32(d, 0x1C),
block_data,
})
}
fn write_inode(&mut self, inode_num: u32, inode: &Inode) -> bool {
let bgd = match BlockGroupDescriptor::read(
&mut self.device, self.gdt_block,
self.sb.inode_block_group(inode_num),
self.sb.sectors_per_block(),
) {
Some(b) => b,
None => return false,
};
let index = self.sb.inode_index_in_group(inode_num);
let inode_offset = (index as usize) * (self.sb.inode_size as usize);
let block_offset = inode_offset / self.sb.block_size;
let offset_in_block = inode_offset % self.sb.block_size;
let mut block_buf = [0u8; 4096];
let block_num = (bgd.inode_table + block_offset as u32) as u64;
read_block(&mut self.device, block_num, self.sb.sectors_per_block(), &mut block_buf);
let d = &mut block_buf[offset_in_block..];
io::write_u16(d, 0x00, inode.mode);
io::write_u32(d, 0x04, inode.size as u32);
io::write_u16(d, 0x1A, inode.links_count);
io::write_u32(d, 0x1C, inode.blocks_count);
io::write_u32(d, 0x20, inode.flags);
d[0x28..0x64].copy_from_slice(&inode.block_data);
io::write_u32(d, 0x6C, (inode.size >> 32) as u32);
io::write_block(&mut self.device, block_num, self.sb.sectors_per_block(), &block_buf)
}
pub fn init_empty_inode(mode: u16) -> Inode {
let mut block_data = [0u8; 60];
io::write_u16(&mut block_data, 0, EXTENT_MAGIC);
io::write_u16(&mut block_data, 2, 0); // entries = 0
io::write_u16(&mut block_data, 4, 4); // max = 4
io::write_u16(&mut block_data, 6, 0); // depth = 0
Inode {
mode,
size: 0,
flags: 0x80000,
links_count: 1,
blocks_count: 0,
block_data,
}
}
pub fn read_inode_pub(&mut self, inode_num: u32) -> Option<Inode> {
self.read_inode(inode_num)
}
pub fn write_inode_pub(&mut self, inode_num: u32, inode: &Inode) -> bool {
self.write_inode(inode_num, inode)
}
pub fn alloc_block(&mut self) -> Option<u32> {
let spb = self.sb.sectors_per_block();
bitmap::alloc_block(&mut self.device, &mut self.sb, self.gdt_block, spb)
}
pub fn free_block(&mut self, block: u32) {
let spb = self.sb.sectors_per_block();
bitmap::free_block(&mut self.device, &mut self.sb, self.gdt_block, block, spb);
}
pub fn alloc_inode(&mut self) -> Option<u32> {
let spb = self.sb.sectors_per_block();
bitmap::alloc_inode(&mut self.device, &mut self.sb, self.gdt_block, spb)
}
pub fn free_inode(&mut self, inode: u32) {
let spb = self.sb.sectors_per_block();
bitmap::free_inode(&mut self.device, &mut self.sb, self.gdt_block, inode, spb);
}
pub fn find_in_dir_pub(&mut self, dir_inode_num: u32, name: &[u8]) -> Option<u32> {
let inode = self.read_inode(dir_inode_num)?;
dir::find_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name)
}
pub fn add_dir_entry(&mut self, dir_inode_num: u32, name: &[u8], child_inode: u32, file_type: u8) -> bool {
let inode = match self.read_inode(dir_inode_num) {
Some(i) => i,
None => return false,
};
dir::add_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name, child_inode, file_type)
}
pub fn remove_dir_entry(&mut self, dir_inode_num: u32, name: &[u8]) -> Option<u32> {
let inode = self.read_inode(dir_inode_num)?;
dir::remove_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name)
}
fn read_extents(&self, inode: &Inode) -> Option<Extent> {
if !inode.uses_extents() { return None; }
let hdr = &inode.block_data;
let magic = read_u16(hdr, 0);
if magic != EXTENT_MAGIC { return None; }
let entries = read_u16(hdr, 2);
let depth = read_u16(hdr, 6);
if depth != 0 || entries == 0 { return None; }
Some(Extent::parse(&hdr[12..24]))
}
fn map_logical_block(&mut self, inode: &Inode, logical_block: u32) -> Option<u64> {
if !inode.uses_extents() { return None; }
let hdr = &inode.block_data;
let magic = read_u16(hdr, 0);
if magic != EXTENT_MAGIC { return None; }
let entries = read_u16(hdr, 2);
let depth = read_u16(hdr, 6);
if depth != 0 {
return None;
}
for i in 0..entries as usize {
let off = 12 + i * 12;
if off + 12 > hdr.len() { break; }
let ext = Extent::parse(&hdr[off..off + 12]);
if logical_block >= ext.logical_block
&& logical_block < ext.logical_block + ext.length as u32
{
return Some(ext.physical_block + (logical_block - ext.logical_block) as u64);
}
}
None
}
fn find_in_dir(&mut self, dir_inode: u32, name: &[u8]) -> Option<u32> {
let inode = self.read_inode(dir_inode)?;
dir::find_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name)
}
fn resolve_path(&mut self, path: &[u8]) -> Option<u32> {
let mut current = ROOT_INODE;
for component in path.split(|&b| b == b'/') {
if component.is_empty() { continue; }
current = self.find_in_dir(current, component)?;
}
Some(current)
}
fn alloc_handle(&self) -> Option<FileHandle> {
for i in 0..MAX_OPEN_FILES {
if self.open_files[i].is_none() {
return Some(FileHandle::new(i as u16));
}
}
None
}
fn resolve_parent<'a>(&mut self, path: &'a [u8]) -> Option<(u32, &'a [u8])> {
let path = if path.starts_with(b"/") { &path[1..] } else { path };
if let Some(last_slash) = path.iter().rposition(|&b| b == b'/') {
let parent_path = &path[..last_slash];
let filename = &path[last_slash + 1..];
let parent_inode = self.resolve_path(parent_path)?;
Some((parent_inode, filename))
} else {
Some((ROOT_INODE, path))
}
}
fn append_extent(block_data: &mut [u8], logical_block: u32, physical_block: u64, length: u16) -> bool {
let magic = read_u16(block_data, 0);
if magic != EXTENT_MAGIC { return false; }
let entries = read_u16(block_data, 2);
let max = read_u16(block_data, 4);
if entries > 0 {
let last_off = 12 + (entries as usize - 1) * 12;
let last = Extent::parse(&block_data[last_off..last_off + 12]);
if last.physical_block + last.length as u64 == physical_block
&& last.logical_block + last.length as u32 == logical_block
{
let new_len = last.length + length;
io::write_u16(block_data, last_off + 4, new_len);
return true;
}
}
if entries >= max { return false; }
let off = 12 + entries as usize * 12;
if off + 12 > block_data.len() { return false; }
io::write_u32(block_data, off, logical_block);
io::write_u16(block_data, off + 4, length);
io::write_u16(block_data, off + 6, (physical_block >> 32) as u16);
io::write_u32(block_data, off + 8, physical_block as u32);
io::write_u16(block_data, 2, entries + 1);
true
}
fn count_extent_blocks(block_data: &[u8; 60]) -> u32 {
let magic = read_u16(block_data, 0);
if magic != EXTENT_MAGIC { return 0; }
let entries = read_u16(block_data, 2);
let mut total = 0u32;
for i in 0..entries as usize {
let off = 12 + i * 12;
if off + 12 > block_data.len() { break; }
total += read_u16(block_data, off + 4) as u32;
}
total
}
fn free_all_blocks(&mut self, inode: &Inode) {
if !inode.uses_extents() { return; }
let hdr = &inode.block_data;
let magic = read_u16(hdr, 0);
if magic != EXTENT_MAGIC { return; }
let entries = read_u16(hdr, 2);
for i in 0..entries as usize {
let off = 12 + i * 12;
if off + 12 > hdr.len() { break; }
let ext = Extent::parse(&hdr[off..off + 12]);
for b in 0..ext.length as u32 {
self.free_block(ext.physical_block as u32 + b);
}
}
}
}
impl<B: BlockDevice> FileSystem for Ext4<B> {

80
crates/servers/storage-server/src/fs/ext4/path.rs Normal file
View File

@@ -0,0 +1,80 @@
//! Path resolution, directory entry operations and allocation wrappers.
use super::{bitmap, dir, Ext4, MAX_OPEN_FILES, ROOT_INODE};
use crate::filesystem::FileHandle;
use port_block_device::BlockDevice;
impl<B: BlockDevice> Ext4<B> {
pub fn alloc_block(&mut self) -> Option<u32> {
let spb = self.sb.sectors_per_block();
bitmap::alloc_block(&mut self.device, &mut self.sb, self.gdt_block, spb)
}
pub fn free_block(&mut self, block: u32) {
let spb = self.sb.sectors_per_block();
bitmap::free_block(&mut self.device, &mut self.sb, self.gdt_block, block, spb);
}
pub fn alloc_inode(&mut self) -> Option<u32> {
let spb = self.sb.sectors_per_block();
bitmap::alloc_inode(&mut self.device, &mut self.sb, self.gdt_block, spb)
}
pub fn free_inode(&mut self, inode: u32) {
let spb = self.sb.sectors_per_block();
bitmap::free_inode(&mut self.device, &mut self.sb, self.gdt_block, inode, spb);
}
pub fn find_in_dir_pub(&mut self, dir_inode_num: u32, name: &[u8]) -> Option<u32> {
let inode = self.read_inode(dir_inode_num)?;
dir::find_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name)
}
pub fn add_dir_entry(&mut self, dir_inode_num: u32, name: &[u8], child_inode: u32, file_type: u8) -> bool {
let inode = match self.read_inode(dir_inode_num) {
Some(i) => i,
None => return false,
};
dir::add_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name, child_inode, file_type)
}
pub fn remove_dir_entry(&mut self, dir_inode_num: u32, name: &[u8]) -> Option<u32> {
let inode = self.read_inode(dir_inode_num)?;
dir::remove_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name)
}
pub(super) fn find_in_dir(&mut self, dir_inode: u32, name: &[u8]) -> Option<u32> {
let inode = self.read_inode(dir_inode)?;
dir::find_entry(&mut self.device, &self.sb, self.gdt_block, &inode, name)
}
pub(super) fn resolve_path(&mut self, path: &[u8]) -> Option<u32> {
let mut current = ROOT_INODE;
for component in path.split(|&b| b == b'/') {
if component.is_empty() { continue; }
current = self.find_in_dir(current, component)?;
}
Some(current)
}
pub(super) fn alloc_handle(&self) -> Option<FileHandle> {
for i in 0..MAX_OPEN_FILES {
if self.open_files[i].is_none() {
return Some(FileHandle::new(i as u16));
}
}
None
}
pub(super) fn resolve_parent<'a>(&mut self, path: &'a [u8]) -> Option<(u32, &'a [u8])> {
let path = if path.starts_with(b"/") { &path[1..] } else { path };
if let Some(last_slash) = path.iter().rposition(|&b| b == b'/') {
let parent_path = &path[..last_slash];
let filename = &path[last_slash + 1..];
let parent_inode = self.resolve_path(parent_path)?;
Some((parent_inode, filename))
} else {
Some((ROOT_INODE, path))
}
}
}

532
crates/servers/storage-server/src/fs/fat16.rs
View File

@@ -1,532 +0,0 @@
use crate::filesystem::{DirEntry, FileHandle, FileName, FileSystem};
use port_block_device::{BlockDevice, SectorId};
const SECTOR_SIZE: usize = 512;
const MAX_OPEN_FILES: usize = 8;
struct Bpb {
bytes_per_sector: u16,
sectors_per_cluster: u8,
reserved_sectors: u16,
num_fats: u8,
root_entry_count: u16,
total_sectors: u16,
sectors_per_fat: u16,
}
impl Bpb {
/// Reads the BPB, refusing geometry the rest of this module cannot
/// work with: the disk is untrusted input like any client request.
fn parse(sector: &[u8]) -> Option<Self> {
if sector.len() < SECTOR_SIZE {
return None;
}
if sector[510] != 0x55 || sector[511] != 0xAA {
return None;
}
let bpb = Self {
bytes_per_sector: u16::from_le_bytes([sector[11], sector[12]]),
sectors_per_cluster: sector[13],
reserved_sectors: u16::from_le_bytes([sector[14], sector[15]]),
num_fats: sector[16],
root_entry_count: u16::from_le_bytes([sector[17], sector[18]]),
total_sectors: u16::from_le_bytes([sector[19], sector[20]]),
sectors_per_fat: u16::from_le_bytes([sector[22], sector[23]]),
};
let usable = bpb.bytes_per_sector as usize == SECTOR_SIZE
&& bpb.sectors_per_cluster.is_power_of_two()
&& bpb.num_fats > 0
&& bpb.sectors_per_fat > 0;
usable.then_some(bpb)
}
fn fat_start(&self) -> u32 {
self.reserved_sectors as u32
}
fn root_dir_start(&self) -> u32 {
self.fat_start() + (self.num_fats as u32) * (self.sectors_per_fat as u32)
}
fn root_dir_sectors(&self) -> u32 {
((self.root_entry_count as u32) * 32 + (self.bytes_per_sector as u32) - 1)
/ (self.bytes_per_sector as u32)
}
fn data_start(&self) -> u32 {
self.root_dir_start() + self.root_dir_sectors()
}
/// The first sector of data cluster `cluster`. Clusters 0 and 1 are
/// reserved and hold no data.
fn cluster_to_sector(&self, cluster: u16) -> Option<u32> {
let index = (cluster as u32).checked_sub(2)?;
Some(self.data_start() + index * (self.sectors_per_cluster as u32))
}
fn cluster_size(&self) -> usize {
self.sectors_per_cluster as usize * SECTOR_SIZE
}
}
#[derive(Clone, Copy)]
struct OpenFile {
first_cluster: u16,
size: usize,
offset: usize,
name: FileName,
}
pub struct Fat16<B: BlockDevice> {
device: B,
bpb: Bpb,
open_files: [Option<OpenFile>; MAX_OPEN_FILES],
}
impl<B: BlockDevice> Fat16<B> {
pub fn mount(mut device: B) -> Option<Self> {
let mut buf = [0u8; SECTOR_SIZE];
if !device.read_sector(SectorId::new(0), &mut buf) {
return None;
}
let bpb = Bpb::parse(&buf)?;
Some(Self {
device,
bpb,
open_files: [const { None }; MAX_OPEN_FILES],
})
}
fn read_fat_entry(&mut self, cluster: u16) -> u16 {
let fat_offset = (cluster as u32) * 2;
let sector = self.bpb.fat_start() + fat_offset / (SECTOR_SIZE as u32);
let offset = (fat_offset % (SECTOR_SIZE as u32)) as usize;
let mut buf = [0u8; SECTOR_SIZE];
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
return 0xFFFF;
}
u16::from_le_bytes([buf[offset], buf[offset + 1]])
}
fn write_fat_entry(&mut self, cluster: u16, value: u16) {
let fat_offset = (cluster as u32) * 2;
let sector = self.bpb.fat_start() + fat_offset / (SECTOR_SIZE as u32);
let offset = (fat_offset % (SECTOR_SIZE as u32)) as usize;
let mut buf = [0u8; SECTOR_SIZE];
self.device.read_sector(SectorId::new(sector), &mut buf);
buf[offset] = value as u8;
buf[offset + 1] = (value >> 8) as u8;
self.device.write_sector(SectorId::new(sector), &buf);
}
fn alloc_cluster(&mut self) -> Option<u16> {
let max = self.bpb.total_sectors as u16 / self.bpb.sectors_per_cluster as u16;
for i in 2..max {
if self.read_fat_entry(i) == 0 {
self.write_fat_entry(i, 0xFFFF);
return Some(i);
}
}
None
}
fn free_chain(&mut self, start: u16) {
let mut cluster = start;
loop {
if cluster < 2 || cluster >= 0xFFF8 {
break;
}
let next = self.read_fat_entry(cluster);
self.write_fat_entry(cluster, 0);
cluster = next;
}
}
fn find_in_root_dir(&mut self, name: &[u8]) -> Option<(u16, usize)> {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
if !self
.device
.read_sector(SectorId::new(self.bpb.root_dir_start() + s), &mut buf)
{
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off] == 0x00 || buf[off] == 0xE5 {
continue;
}
if buf[off..off + 11] == fat_name {
let cluster = u16::from_le_bytes([buf[off + 26], buf[off + 27]]);
let size = u32::from_le_bytes([
buf[off + 28],
buf[off + 29],
buf[off + 30],
buf[off + 31],
]);
return Some((cluster, size as usize));
}
}
}
None
}
fn create_dir_entry(&mut self, name: &[u8], cluster: u16) -> bool {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
let sector = self.bpb.root_dir_start() + s;
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off] == 0x00 || buf[off] == 0xE5 {
buf[off..off + 11].copy_from_slice(&fat_name);
buf[off + 11] = 0x20;
for b in &mut buf[off + 12..off + 26] {
*b = 0;
}
buf[off + 26] = cluster as u8;
buf[off + 27] = (cluster >> 8) as u8;
for b in &mut buf[off + 28..off + 32] {
*b = 0;
}
self.device.write_sector(SectorId::new(sector), &buf);
return true;
}
}
}
false
}
fn delete_dir_entry(&mut self, name: &[u8]) -> Option<u16> {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
let sector = self.bpb.root_dir_start() + s;
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off..off + 11] == fat_name {
let cluster = u16::from_le_bytes([buf[off + 26], buf[off + 27]]);
buf[off] = 0xE5;
self.device.write_sector(SectorId::new(sector), &buf);
return Some(cluster);
}
}
}
None
}
fn update_dir_size(&mut self, name: &[u8], size: u32, cluster: u16) {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
let sector = self.bpb.root_dir_start() + s;
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off..off + 11] == fat_name {
buf[off + 28..off + 32].copy_from_slice(&size.to_le_bytes());
buf[off + 26] = cluster as u8;
buf[off + 27] = (cluster >> 8) as u8;
self.device.write_sector(SectorId::new(sector), &buf);
return;
}
}
}
}
fn follow_chain(&mut self, start: u16, skip_clusters: usize) -> u16 {
let mut cluster = start;
for _ in 0..skip_clusters {
let next = self.read_fat_entry(cluster);
if next >= 0xFFF8 {
return cluster;
}
cluster = next;
}
cluster
}
/// The open-file slot `handle` names; `None` for handles past the
/// table, which come straight from clients.
fn slot(&mut self, handle: FileHandle) -> Option<&mut Option<OpenFile>> {
self.open_files.get_mut(handle.raw() as usize)
}
fn alloc_handle(&self) -> Option<FileHandle> {
for i in 0..MAX_OPEN_FILES {
if self.open_files[i].is_none() {
return Some(FileHandle::new(i as u16));
}
}
None
}
}
impl<B: BlockDevice> FileSystem for Fat16<B> {
fn open(&mut self, path: &[u8]) -> Option<FileHandle> {
let (cluster, size) = self.find_in_root_dir(path)?;
let handle = self.alloc_handle()?;
*self.slot(handle)? = Some(OpenFile {
first_cluster: cluster,
size,
offset: 0,
name: FileName::from_bytes(path),
});
Some(handle)
}
fn read(&mut self, handle: FileHandle, buf: &mut [u8]) -> Option<usize> {
let file = (*self.slot(handle)?)?;
if file.offset >= file.size {
return Some(0);
}
let remaining = file.size - file.offset;
let to_read = buf.len().min(remaining);
let cs = self.bpb.cluster_size();
let skip_clusters = file.offset / cs;
let mut cluster = self.follow_chain(file.first_cluster, skip_clusters);
let mut skip = file.offset % cs;
let mut read = 0;
let mut sector_buf = [0u8; SECTOR_SIZE];
while read < to_read {
let sector_in_cluster = skip / SECTOR_SIZE;
let byte_in_sector = skip % SECTOR_SIZE;
let Some(base) = self.bpb.cluster_to_sector(cluster) else {
break;
};
let sector = base + sector_in_cluster as u32;
if !self
.device
.read_sector(SectorId::new(sector), &mut sector_buf)
{
break;
}
let chunk = (SECTOR_SIZE - byte_in_sector).min(to_read - read);
buf[read..read + chunk]
.copy_from_slice(&sector_buf[byte_in_sector..byte_in_sector + chunk]);
read += chunk;
skip += chunk;
if skip >= cs {
let next = self.read_fat_entry(cluster);
if next >= 0xFFF8 {
break;
}
cluster = next;
skip = 0;
}
}
if let Some(Some(f)) = self.slot(handle) {
f.offset += read;
}
Some(read)
}
fn write(&mut self, handle: FileHandle, buf: &[u8]) -> Option<usize> {
let mut file = (*self.slot(handle)?)?;
let cs = self.bpb.cluster_size();
if file.first_cluster < 2 {
let c = self.alloc_cluster()?;
file.first_cluster = c;
}
let skip_clusters = file.offset / cs;
let mut cluster = self.follow_chain(file.first_cluster, skip_clusters);
let mut pos = file.offset % cs;
let mut written = 0;
let mut sector_buf = [0u8; SECTOR_SIZE];
while written < buf.len() {
let sector_in_cluster = pos / SECTOR_SIZE;
let byte_in_sector = pos % SECTOR_SIZE;
let Some(base) = self.bpb.cluster_to_sector(cluster) else {
break;
};
let sector = base + sector_in_cluster as u32;
if !self.device.read_sector(SectorId::new(sector), &mut sector_buf) {
break;
}
let chunk = (SECTOR_SIZE - byte_in_sector).min(buf.len() - written);
sector_buf[byte_in_sector..byte_in_sector + chunk]
.copy_from_slice(&buf[written..written + chunk]);
// Bytes count as written only once they reached the disk.
if !self.device.write_sector(SectorId::new(sector), &sector_buf) {
break;
}
written += chunk;
pos += chunk;
if pos >= cs {
let next = self.read_fat_entry(cluster);
if next >= 0xFFF8 {
if written < buf.len() {
if let Some(new_c) = self.alloc_cluster() {
self.write_fat_entry(cluster, new_c);
cluster = new_c;
} else {
break;
}
}
} else {
cluster = next;
}
pos = 0;
}
}
file.offset += written;
if file.offset > file.size {
file.size = file.offset;
}
*self.slot(handle)? = Some(file);
Some(written)
}
fn close(&mut self, handle: FileHandle) {
let Some(file) = self.slot(handle).and_then(Option::take) else {
return;
};
let mut name_buf = [0u8; 32];
let name_bytes = file.name.as_bytes();
let len = name_bytes.len().min(32);
name_buf[..len].copy_from_slice(&name_bytes[..len]);
self.update_dir_size(&name_buf[..len], file.size as u32, file.first_cluster);
}
fn list_dir(&mut self, _path: &[u8], entries: &mut [DirEntry]) -> Option<usize> {
let mut buf = [0u8; SECTOR_SIZE];
let mut count = 0;
for s in 0..self.bpb.root_dir_sectors() {
if !self
.device
.read_sector(SectorId::new(self.bpb.root_dir_start() + s), &mut buf)
{
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
if count >= entries.len() {
return Some(count);
}
let off = i * 32;
if buf[off] == 0x00 {
return Some(count);
}
if buf[off] == 0xE5 || buf[off + 11] & 0x08 != 0 {
continue;
}
let size = u32::from_le_bytes([
buf[off + 28],
buf[off + 29],
buf[off + 30],
buf[off + 31],
]);
entries[count] = DirEntry {
name: from_fat_name(&buf[off..off + 11]),
size: size as usize,
is_dir: buf[off + 11] & 0x10 != 0,
};
count += 1;
}
}
Some(count)
}
fn create(&mut self, path: &[u8]) -> Option<FileHandle> {
if self.find_in_root_dir(path).is_some() {
return None;
}
let cluster = self.alloc_cluster()?;
if !self.create_dir_entry(path, cluster) {
self.write_fat_entry(cluster, 0);
return None;
}
let handle = self.alloc_handle()?;
*self.slot(handle)? = Some(OpenFile {
first_cluster: cluster,
size: 0,
offset: 0,
name: FileName::from_bytes(path),
});
Some(handle)
}
fn delete(&mut self, path: &[u8]) -> bool {
if let Some(cluster) = self.delete_dir_entry(path) {
self.free_chain(cluster);
true
} else {
false
}
}
fn file_size(&mut self, handle: FileHandle) -> Option<usize> {
self.slot(handle)?.as_ref().map(|f| f.size)
}
fn mkdir(&mut self, _path: &[u8]) -> bool {
false
}
fn writable(&self) -> bool {
self.device.writable()
}
}
fn to_fat_name(name: &[u8]) -> [u8; 11] {
let mut fat = [b' '; 11];
let dot_pos = name.iter().position(|&b| b == b'.').unwrap_or(name.len());
for i in 0..dot_pos.min(8) {
fat[i] = name[i].to_ascii_uppercase();
}
if dot_pos < name.len() {
for i in 0..(name.len() - dot_pos - 1).min(3) {
fat[8 + i] = name[dot_pos + 1 + i].to_ascii_uppercase();
}
}
fat
}
fn from_fat_name(raw: &[u8]) -> FileName {
let mut buf = [0u8; 32];
let mut pos = 0;
let name_end = raw[..8]
.iter()
.rposition(|&b| b != b' ')
.map(|i| i + 1)
.unwrap_or(0);
for i in 0..name_end {
buf[pos] = raw[i].to_ascii_lowercase();
pos += 1;
}
let ext_end = raw[8..11]
.iter()
.rposition(|&b| b != b' ')
.map(|i| i + 1)
.unwrap_or(0);
if ext_end > 0 {
buf[pos] = b'.';
pos += 1;
for i in 0..ext_end {
buf[pos] = raw[8 + i].to_ascii_lowercase();
pos += 1;
}
}
FileName::from_bytes(&buf[..pos])
}

68
crates/servers/storage-server/src/fs/fat16/bpb.rs Normal file
View File

@@ -0,0 +1,68 @@
//! BIOS parameter block: disk geometry.
use super::SECTOR_SIZE;
pub(super) struct Bpb {
pub(super) bytes_per_sector: u16,
pub(super) sectors_per_cluster: u8,
pub(super) reserved_sectors: u16,
pub(super) num_fats: u8,
pub(super) root_entry_count: u16,
pub(super) total_sectors: u16,
pub(super) sectors_per_fat: u16,
}
impl Bpb {
/// Reads the BPB, refusing geometry the rest of this module cannot
/// work with: the disk is untrusted input like any client request.
pub(super) fn parse(sector: &[u8]) -> Option<Self> {
if sector.len() < SECTOR_SIZE {
return None;
}
if sector[510] != 0x55 || sector[511] != 0xAA {
return None;
}
let bpb = Self {
bytes_per_sector: u16::from_le_bytes([sector[11], sector[12]]),
sectors_per_cluster: sector[13],
reserved_sectors: u16::from_le_bytes([sector[14], sector[15]]),
num_fats: sector[16],
root_entry_count: u16::from_le_bytes([sector[17], sector[18]]),
total_sectors: u16::from_le_bytes([sector[19], sector[20]]),
sectors_per_fat: u16::from_le_bytes([sector[22], sector[23]]),
};
let usable = bpb.bytes_per_sector as usize == SECTOR_SIZE
&& bpb.sectors_per_cluster.is_power_of_two()
&& bpb.num_fats > 0
&& bpb.sectors_per_fat > 0;
usable.then_some(bpb)
}
pub(super) fn fat_start(&self) -> u32 {
self.reserved_sectors as u32
}
pub(super) fn root_dir_start(&self) -> u32 {
self.fat_start() + (self.num_fats as u32) * (self.sectors_per_fat as u32)
}
pub(super) fn root_dir_sectors(&self) -> u32 {
((self.root_entry_count as u32) * 32 + (self.bytes_per_sector as u32) - 1)
/ (self.bytes_per_sector as u32)
}
pub(super) fn data_start(&self) -> u32 {
self.root_dir_start() + self.root_dir_sectors()
}
/// The first sector of data cluster `cluster`. Clusters 0 and 1 are
/// reserved and hold no data.
pub(super) fn cluster_to_sector(&self, cluster: u16) -> Option<u32> {
let index = (cluster as u32).checked_sub(2)?;
Some(self.data_start() + index * (self.sectors_per_cluster as u32))
}
pub(super) fn cluster_size(&self) -> usize {
self.sectors_per_cluster as usize * SECTOR_SIZE
}
}

151
crates/servers/storage-server/src/fs/fat16/dir.rs Normal file
View File

@@ -0,0 +1,151 @@
//! Root directory entries and 8.3 names.
use super::Fat16;
use super::SECTOR_SIZE;
use crate::filesystem::FileName;
use port_block_device::{BlockDevice, SectorId};
impl<B: BlockDevice> Fat16<B> {
pub(super) fn find_in_root_dir(&mut self, name: &[u8]) -> Option<(u16, usize)> {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
if !self
.device
.read_sector(SectorId::new(self.bpb.root_dir_start() + s), &mut buf)
{
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off] == 0x00 || buf[off] == 0xE5 {
continue;
}
if buf[off..off + 11] == fat_name {
let cluster = u16::from_le_bytes([buf[off + 26], buf[off + 27]]);
let size = u32::from_le_bytes([
buf[off + 28],
buf[off + 29],
buf[off + 30],
buf[off + 31],
]);
return Some((cluster, size as usize));
}
}
}
None
}
pub(super) fn create_dir_entry(&mut self, name: &[u8], cluster: u16) -> bool {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
let sector = self.bpb.root_dir_start() + s;
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off] == 0x00 || buf[off] == 0xE5 {
buf[off..off + 11].copy_from_slice(&fat_name);
buf[off + 11] = 0x20;
for b in &mut buf[off + 12..off + 26] {
*b = 0;
}
buf[off + 26] = cluster as u8;
buf[off + 27] = (cluster >> 8) as u8;
for b in &mut buf[off + 28..off + 32] {
*b = 0;
}
self.device.write_sector(SectorId::new(sector), &buf);
return true;
}
}
}
false
}
pub(super) fn delete_dir_entry(&mut self, name: &[u8]) -> Option<u16> {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
let sector = self.bpb.root_dir_start() + s;
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off..off + 11] == fat_name {
let cluster = u16::from_le_bytes([buf[off + 26], buf[off + 27]]);
buf[off] = 0xE5;
self.device.write_sector(SectorId::new(sector), &buf);
return Some(cluster);
}
}
}
None
}
pub(super) fn update_dir_size(&mut self, name: &[u8], size: u32, cluster: u16) {
let mut buf = [0u8; SECTOR_SIZE];
let fat_name = to_fat_name(name);
for s in 0..self.bpb.root_dir_sectors() {
let sector = self.bpb.root_dir_start() + s;
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
let off = i * 32;
if buf[off..off + 11] == fat_name {
buf[off + 28..off + 32].copy_from_slice(&size.to_le_bytes());
buf[off + 26] = cluster as u8;
buf[off + 27] = (cluster >> 8) as u8;
self.device.write_sector(SectorId::new(sector), &buf);
return;
}
}
}
}
}
pub(super) fn to_fat_name(name: &[u8]) -> [u8; 11] {
let mut fat = [b' '; 11];
let dot_pos = name.iter().position(|&b| b == b'.').unwrap_or(name.len());
for i in 0..dot_pos.min(8) {
fat[i] = name[i].to_ascii_uppercase();
}
if dot_pos < name.len() {
for i in 0..(name.len() - dot_pos - 1).min(3) {
fat[8 + i] = name[dot_pos + 1 + i].to_ascii_uppercase();
}
}
fat
}
pub(super) fn from_fat_name(raw: &[u8]) -> FileName {
let mut buf = [0u8; 32];
let mut pos = 0;
let name_end = raw[..8]
.iter()
.rposition(|&b| b != b' ')
.map(|i| i + 1)
.unwrap_or(0);
for i in 0..name_end {
buf[pos] = raw[i].to_ascii_lowercase();
pos += 1;
}
let ext_end = raw[8..11]
.iter()
.rposition(|&b| b != b' ')
.map(|i| i + 1)
.unwrap_or(0);
if ext_end > 0 {
buf[pos] = b'.';
pos += 1;
for i in 0..ext_end {
buf[pos] = raw[8 + i].to_ascii_lowercase();
pos += 1;
}
}
FileName::from_bytes(&buf[..pos])
}

64
crates/servers/storage-server/src/fs/fat16/fat.rs Normal file
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@@ -0,0 +1,64 @@
//! FAT table: cluster allocation and chains.
use super::Fat16;
use super::SECTOR_SIZE;
use port_block_device::{BlockDevice, SectorId};
impl<B: BlockDevice> Fat16<B> {
pub(super) fn read_fat_entry(&mut self, cluster: u16) -> u16 {
let fat_offset = (cluster as u32) * 2;
let sector = self.bpb.fat_start() + fat_offset / (SECTOR_SIZE as u32);
let offset = (fat_offset % (SECTOR_SIZE as u32)) as usize;
let mut buf = [0u8; SECTOR_SIZE];
if !self.device.read_sector(SectorId::new(sector), &mut buf) {
return 0xFFFF;
}
u16::from_le_bytes([buf[offset], buf[offset + 1]])
}
pub(super) fn write_fat_entry(&mut self, cluster: u16, value: u16) {
let fat_offset = (cluster as u32) * 2;
let sector = self.bpb.fat_start() + fat_offset / (SECTOR_SIZE as u32);
let offset = (fat_offset % (SECTOR_SIZE as u32)) as usize;
let mut buf = [0u8; SECTOR_SIZE];
self.device.read_sector(SectorId::new(sector), &mut buf);
buf[offset] = value as u8;
buf[offset + 1] = (value >> 8) as u8;
self.device.write_sector(SectorId::new(sector), &buf);
}
pub(super) fn alloc_cluster(&mut self) -> Option<u16> {
let max = self.bpb.total_sectors as u16 / self.bpb.sectors_per_cluster as u16;
for i in 2..max {
if self.read_fat_entry(i) == 0 {
self.write_fat_entry(i, 0xFFFF);
return Some(i);
}
}
None
}
pub(super) fn free_chain(&mut self, start: u16) {
let mut cluster = start;
loop {
if cluster < 2 || cluster >= 0xFFF8 {
break;
}
let next = self.read_fat_entry(cluster);
self.write_fat_entry(cluster, 0);
cluster = next;
}
}
pub(super) fn follow_chain(&mut self, start: u16, skip_clusters: usize) -> u16 {
let mut cluster = start;
for _ in 0..skip_clusters {
let next = self.read_fat_entry(cluster);
if next >= 0xFFF8 {
return cluster;
}
cluster = next;
}
cluster
}
}

275
crates/servers/storage-server/src/fs/fat16/mod.rs Normal file
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//! FAT16 filesystem over a block device (root directory only).
mod bpb;
mod dir;
mod fat;
use crate::filesystem::{DirEntry, FileHandle, FileName, FileSystem};
use bpb::Bpb;
use dir::from_fat_name;
use port_block_device::{BlockDevice, SectorId};
const SECTOR_SIZE: usize = 512;
const MAX_OPEN_FILES: usize = 8;
#[derive(Clone, Copy)]
struct OpenFile {
first_cluster: u16,
size: usize,
offset: usize,
name: FileName,
}
pub struct Fat16<B: BlockDevice> {
device: B,
bpb: Bpb,
open_files: [Option<OpenFile>; MAX_OPEN_FILES],
}
impl<B: BlockDevice> Fat16<B> {
pub fn mount(mut device: B) -> Option<Self> {
let mut buf = [0u8; SECTOR_SIZE];
if !device.read_sector(SectorId::new(0), &mut buf) {
return None;
}
let bpb = Bpb::parse(&buf)?;
Some(Self {
device,
bpb,
open_files: [const { None }; MAX_OPEN_FILES],
})
}
/// The open-file slot `handle` names; `None` for handles past the
/// table, which come straight from clients.
fn slot(&mut self, handle: FileHandle) -> Option<&mut Option<OpenFile>> {
self.open_files.get_mut(handle.raw() as usize)
}
fn alloc_handle(&self) -> Option<FileHandle> {
for i in 0..MAX_OPEN_FILES {
if self.open_files[i].is_none() {
return Some(FileHandle::new(i as u16));
}
}
None
}
}
impl<B: BlockDevice> FileSystem for Fat16<B> {
fn open(&mut self, path: &[u8]) -> Option<FileHandle> {
let (cluster, size) = self.find_in_root_dir(path)?;
let handle = self.alloc_handle()?;
*self.slot(handle)? = Some(OpenFile {
first_cluster: cluster,
size,
offset: 0,
name: FileName::from_bytes(path),
});
Some(handle)
}
fn read(&mut self, handle: FileHandle, buf: &mut [u8]) -> Option<usize> {
let file = (*self.slot(handle)?)?;
if file.offset >= file.size {
return Some(0);
}
let remaining = file.size - file.offset;
let to_read = buf.len().min(remaining);
let cs = self.bpb.cluster_size();
let skip_clusters = file.offset / cs;
let mut cluster = self.follow_chain(file.first_cluster, skip_clusters);
let mut skip = file.offset % cs;
let mut read = 0;
let mut sector_buf = [0u8; SECTOR_SIZE];
while read < to_read {
let sector_in_cluster = skip / SECTOR_SIZE;
let byte_in_sector = skip % SECTOR_SIZE;
let Some(base) = self.bpb.cluster_to_sector(cluster) else {
break;
};
let sector = base + sector_in_cluster as u32;
if !self
.device
.read_sector(SectorId::new(sector), &mut sector_buf)
{
break;
}
let chunk = (SECTOR_SIZE - byte_in_sector).min(to_read - read);
buf[read..read + chunk]
.copy_from_slice(&sector_buf[byte_in_sector..byte_in_sector + chunk]);
read += chunk;
skip += chunk;
if skip >= cs {
let next = self.read_fat_entry(cluster);
if next >= 0xFFF8 {
break;
}
cluster = next;
skip = 0;
}
}
if let Some(Some(f)) = self.slot(handle) {
f.offset += read;
}
Some(read)
}
fn write(&mut self, handle: FileHandle, buf: &[u8]) -> Option<usize> {
let mut file = (*self.slot(handle)?)?;
let cs = self.bpb.cluster_size();
if file.first_cluster < 2 {
let c = self.alloc_cluster()?;
file.first_cluster = c;
}
let skip_clusters = file.offset / cs;
let mut cluster = self.follow_chain(file.first_cluster, skip_clusters);
let mut pos = file.offset % cs;
let mut written = 0;
let mut sector_buf = [0u8; SECTOR_SIZE];
while written < buf.len() {
let sector_in_cluster = pos / SECTOR_SIZE;
let byte_in_sector = pos % SECTOR_SIZE;
let Some(base) = self.bpb.cluster_to_sector(cluster) else {
break;
};
let sector = base + sector_in_cluster as u32;
if !self.device.read_sector(SectorId::new(sector), &mut sector_buf) {
break;
}
let chunk = (SECTOR_SIZE - byte_in_sector).min(buf.len() - written);
sector_buf[byte_in_sector..byte_in_sector + chunk]
.copy_from_slice(&buf[written..written + chunk]);
// Bytes count as written only once they reached the disk.
if !self.device.write_sector(SectorId::new(sector), &sector_buf) {
break;
}
written += chunk;
pos += chunk;
if pos >= cs {
let next = self.read_fat_entry(cluster);
if next >= 0xFFF8 {
if written < buf.len() {
if let Some(new_c) = self.alloc_cluster() {
self.write_fat_entry(cluster, new_c);
cluster = new_c;
} else {
break;
}
}
} else {
cluster = next;
}
pos = 0;
}
}
file.offset += written;
if file.offset > file.size {
file.size = file.offset;
}
*self.slot(handle)? = Some(file);
Some(written)
}
fn close(&mut self, handle: FileHandle) {
let Some(file) = self.slot(handle).and_then(Option::take) else {
return;
};
let mut name_buf = [0u8; 32];
let name_bytes = file.name.as_bytes();
let len = name_bytes.len().min(32);
name_buf[..len].copy_from_slice(&name_bytes[..len]);
self.update_dir_size(&name_buf[..len], file.size as u32, file.first_cluster);
}
fn list_dir(&mut self, _path: &[u8], entries: &mut [DirEntry]) -> Option<usize> {
let mut buf = [0u8; SECTOR_SIZE];
let mut count = 0;
for s in 0..self.bpb.root_dir_sectors() {
if !self
.device
.read_sector(SectorId::new(self.bpb.root_dir_start() + s), &mut buf)
{
continue;
}
for i in 0..(SECTOR_SIZE / 32) {
if count >= entries.len() {
return Some(count);
}
let off = i * 32;
if buf[off] == 0x00 {
return Some(count);
}
if buf[off] == 0xE5 || buf[off + 11] & 0x08 != 0 {
continue;
}
let size = u32::from_le_bytes([
buf[off + 28],
buf[off + 29],
buf[off + 30],
buf[off + 31],
]);
entries[count] = DirEntry {
name: from_fat_name(&buf[off..off + 11]),
size: size as usize,
is_dir: buf[off + 11] & 0x10 != 0,
};
count += 1;
}
}
Some(count)
}
fn create(&mut self, path: &[u8]) -> Option<FileHandle> {
if self.find_in_root_dir(path).is_some() {
return None;
}
let cluster = self.alloc_cluster()?;
if !self.create_dir_entry(path, cluster) {
self.write_fat_entry(cluster, 0);
return None;
}
let handle = self.alloc_handle()?;
*self.slot(handle)? = Some(OpenFile {
first_cluster: cluster,
size: 0,
offset: 0,
name: FileName::from_bytes(path),
});
Some(handle)
}
fn delete(&mut self, path: &[u8]) -> bool {
if let Some(cluster) = self.delete_dir_entry(path) {
self.free_chain(cluster);
true
} else {
false
}
}
fn file_size(&mut self, handle: FileHandle) -> Option<usize> {
self.slot(handle)?.as_ref().map(|f| f.size)
}
fn mkdir(&mut self, _path: &[u8]) -> bool {
false
}
fn writable(&self) -> bool {
self.device.writable()
}
}