file.c

//
// File descriptors
//

#include "types.h"
#include "defs.h"
#include "param.h"
#include "fs.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "file.h"

struct devsw devsw[NDEV];
struct {
  struct spinlock lock;
  struct file file[NFILE];
} ftable;

void fileinit(void) { initlock(&ftable.lock, "ftable"); }

// Allocate a file structure.
struct file *filealloc(void) {
  struct file *f;

  acquire(&ftable.lock);
  for (f = ftable.file; f < ftable.file + NFILE; f++) {
    if (f->ref == 0) {
      f->ref = 1;
      release(&ftable.lock);
      return f;
    }
  }
  release(&ftable.lock);
  return 0;
}

// Increment ref count for file f.
struct file *filedup(struct file *f) {
  acquire(&ftable.lock);
  if (f->ref < 1)
    panic("filedup");
  f->ref++;
  release(&ftable.lock);
  return f;
}

// Close file f.  (Decrement ref count, close when reaches 0.)
void fileclose(struct file *f) {
  struct file ff;

  acquire(&ftable.lock);
  if (f->ref < 1)
    panic("fileclose");
  if (--f->ref > 0) {
    release(&ftable.lock);
    return;
  }
  ff = *f;
  f->ref = 0;
  f->type = FD_NONE;
  release(&ftable.lock);

  if (ff.type == FD_PIPE)
    pipeclose(ff.pipe, ff.writable);
  else if (ff.type == FD_INODE) {
    begin_op();
    iput(ff.ip);
    end_op();
  }
}

// Get metadata about file f.
int filestat(struct file *f, struct stat *st) {
  if (f->type == FD_INODE) {
    ilock(f->ip);
    stati(f->ip, st);
    iunlock(f->ip);
    return 0;
  }
  return -1;
}

// Read from file f.
int fileread(struct file *f, char *addr, int n) {
  int r;

  if (f->readable == 0)
    return -1;
  if (f->type == FD_PIPE)
    return piperead(f->pipe, addr, n);
  if (f->type == FD_INODE) {
    ilock(f->ip);
    if ((r = readi(f->ip, addr, f->off, n)) > 0)
      f->off += r;
    iunlock(f->ip);
    return r;
  }
  panic("fileread");
}

// PAGEBREAK!
// Write to file f.
int filewrite(struct file *f, char *addr, int n) {
  int r;

  if (f->writable == 0)
    return -1;
  if (f->type == FD_PIPE)
    return pipewrite(f->pipe, addr, n);
  if (f->type == FD_INODE) {
    // write a few blocks at a time to avoid exceeding
    // the maximum log transaction size, including
    // i-node, indirect block, allocation blocks,
    // and 2 blocks of slop for non-aligned writes.
    // this really belongs lower down, since writei()
    // might be writing a device like the console.
    int max = ((MAXOPBLOCKS - 1 - 1 - 2) / 2) * 512;
    int i = 0;
    while (i < n) {
      int n1 = n - i;
      if (n1 > max)
        n1 = max;

      begin_op();
      ilock(f->ip);
      if ((r = writei(f->ip, addr + i, f->off, n1)) > 0)
        f->off += r;
      iunlock(f->ip);
      end_op();

      if (r < 0)
        break;
      if (r != n1)
        panic("short filewrite");
      i += r;
    }
    return i == n ? n : -1;
  }
  panic("filewrite");
}