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