fs.c

// File system implementation.  Five layers:
//   + Blocks: allocator for raw disk blocks.
//   + Log: crash recovery for multi-step updates.
//   + Files: inode allocator, reading, writing, metadata.
//   + Directories: inode with special contents (list of other inodes!)
//   + Names: paths like /usr/rtm/xv6/fs.c for convenient naming.
//
// This file contains the low-level file system manipulation
// routines.  The (higher-level) system call implementations
// are in sysfile.c.

#include "types.h"
#include "riscv.h"
#include "defs.h"
#include "param.h"
#include "include/stat.h"
#include "include/spinlock.h"
#include "proc.h"
#include "sleeplock.h"
#include "fs.h"
#include "buf.h"
#include "file.h"

#define min(a, b) ((a) < (b) ? (a) : (b))
// there should be one superblock per disk device, but we run with
// only one device
struct superblock sb; 

// Read the super block.
static void
readsb(int dev, struct superblock *sb)
{
  struct buf *bp;

  bp = bread(dev, 1);
  memmove(sb, bp->data, sizeof(*sb));
  brelse(bp);
}

// Init fs
void
fsinit(int dev) {
  readsb(dev, &sb);
  if(sb.magic != FSMAGIC)
    panic("invalid file system");
  initlog(dev, &sb);
}

// Zero a block.
static void
bzero(int dev, int bno)
{
  struct buf *bp;

  bp = bread(dev, bno);
  memset(bp->data, 0, BSIZE);
  log_write(bp);
  brelse(bp);
}

// Blocks.

// Allocate a zeroed disk block.
// returns 0 if out of disk space.
static uint
balloc(uint dev)
{
  int b, bi, m;
  struct buf *bp;