Read FSInfo sector on mount and use it during cluster allocation

This commit is contained in:
Rafał Harabień 2018-05-12 23:17:45 +02:00
parent 0e6b0a07a4
commit 4793d20977
2 changed files with 69 additions and 5 deletions

View File

@ -4,7 +4,7 @@ use io::prelude::*;
use io::{Error, ErrorKind, SeekFrom}; use io::{Error, ErrorKind, SeekFrom};
use io; use io;
use byteorder::LittleEndian; use byteorder::LittleEndian;
use byteorder_ext::ReadBytesExt; use byteorder_ext::{ReadBytesExt, WriteBytesExt};
use file::File; use file::File;
use dir::{DirRawStream, Dir}; use dir::{DirRawStream, Dir};
@ -205,6 +205,57 @@ impl Default for BootRecord {
} }
} }
struct FsInfoSector {
#[allow(dead_code)]
free_cluster_count: u32,
next_free_cluster: u32,
}
impl FsInfoSector {
const LEAD_SIG: u32 = 0x41615252;
const STRUC_SIG: u32 = 0x61417272;
const TRAIL_SIG: u32 = 0xAA550000;
fn deserialize(rdr: &mut Read) -> io::Result<FsInfoSector> {
let lead_sig = rdr.read_u32::<LittleEndian>()?;
if lead_sig != Self::LEAD_SIG {
return Err(Error::new(ErrorKind::Other, "invalid lead_sig in FsInfo sector"));
}
let mut reserved = [0u8; 480];
rdr.read_exact(&mut reserved)?;
let struc_sig = rdr.read_u32::<LittleEndian>()?;
if struc_sig != Self::STRUC_SIG {
return Err(Error::new(ErrorKind::Other, "invalid struc_sig in FsInfo sector"));
}
let free_cluster_count = rdr.read_u32::<LittleEndian>()?;
let next_free_cluster = rdr.read_u32::<LittleEndian>()?;
let mut reserved2 = [0u8; 12];
rdr.read_exact(&mut reserved2)?;
let trail_sig = rdr.read_u32::<LittleEndian>()?;
if trail_sig != Self::TRAIL_SIG {
return Err(Error::new(ErrorKind::Other, "invalid trail_sig in FsInfo sector"));
}
Ok(FsInfoSector {
free_cluster_count, next_free_cluster
})
}
// TODO: save modified FsInfo secton on unmount
#[allow(dead_code)]
fn serialize(&self, wrt: &mut Write) -> io::Result<()> {
wrt.write_u32::<LittleEndian>(Self::LEAD_SIG)?;
let reserved = [0u8; 480];
wrt.write(&reserved)?;
wrt.write_u32::<LittleEndian>(Self::STRUC_SIG)?;
wrt.write_u32::<LittleEndian>(self.free_cluster_count)?;
wrt.write_u32::<LittleEndian>(self.next_free_cluster)?;
let reserved2 = [0u8; 12];
wrt.write(&reserved2)?;
wrt.write_u32::<LittleEndian>(Self::TRAIL_SIG)?;
Ok(())
}
}
/// FAT filesystem options. /// FAT filesystem options.
#[derive(Debug, Clone, Copy)] #[derive(Debug, Clone, Copy)]
pub struct FsOptions { pub struct FsOptions {
@ -235,6 +286,7 @@ pub struct FileSystem<'a> {
bpb: BiosParameterBlock, bpb: BiosParameterBlock,
first_data_sector: u32, first_data_sector: u32,
root_dir_sectors: u32, root_dir_sectors: u32,
fs_info: Option<FsInfoSector>,
} }
impl <'a> FileSystem<'a> { impl <'a> FileSystem<'a> {
@ -272,6 +324,13 @@ impl <'a> FileSystem<'a> {
let total_clusters = data_sectors / bpb.sectors_per_cluster as u32; let total_clusters = data_sectors / bpb.sectors_per_cluster as u32;
let fat_type = FatType::from_clusters(total_clusters); let fat_type = FatType::from_clusters(total_clusters);
let fs_info = if fat_type == FatType::Fat32 {
disk.seek(SeekFrom::Start(bpb.fs_info_sector as u64 * 512))?;
Some(FsInfoSector::deserialize(disk)?)
} else {
None
};
Ok(FileSystem { Ok(FileSystem {
disk: RefCell::new(disk), disk: RefCell::new(disk),
options, options,
@ -279,6 +338,7 @@ impl <'a> FileSystem<'a> {
bpb: bpb, bpb: bpb,
first_data_sector, first_data_sector,
root_dir_sectors, root_dir_sectors,
fs_info,
}) })
} }
@ -354,8 +414,12 @@ impl <'a> FileSystem<'a> {
} }
pub(crate) fn alloc_cluster(&self, prev_cluster: Option<u32>) -> io::Result<u32> { pub(crate) fn alloc_cluster(&self, prev_cluster: Option<u32>) -> io::Result<u32> {
let mut disk_slice = self.fat_slice(); let hint = match self.fs_info {
alloc_cluster(&mut disk_slice, self.fat_type, prev_cluster) Some(ref info) => Some(info.next_free_cluster),
None => None,
};
let mut fat = self.fat_slice();
alloc_cluster(&mut fat, self.fat_type, prev_cluster, hint)
} }
pub fn read_status_flags(&self) -> io::Result<FsStatusFlags> { pub fn read_status_flags(&self) -> io::Result<FsStatusFlags> {

View File

@ -61,8 +61,8 @@ fn find_free_cluster(fat: &mut ReadSeek, fat_type: FatType, cluster: u32) -> io:
} }
} }
pub(crate) fn alloc_cluster(fat: &mut DiskSlice, fat_type: FatType, prev_cluster: Option<u32>) -> io::Result<u32> { pub(crate) fn alloc_cluster(fat: &mut DiskSlice, fat_type: FatType, prev_cluster: Option<u32>, hint: Option<u32>) -> io::Result<u32> {
let new_cluster = find_free_cluster(fat, fat_type, 2)?; let new_cluster = find_free_cluster(fat, fat_type, hint.unwrap_or(2))?;
write_fat(fat, fat_type, new_cluster, FatValue::EndOfChain)?; write_fat(fat, fat_type, new_cluster, FatValue::EndOfChain)?;
match prev_cluster { match prev_cluster {
Some(n) => write_fat(fat, fat_type, n, FatValue::Data(new_cluster))?, Some(n) => write_fat(fat, fat_type, n, FatValue::Data(new_cluster))?,