file.c

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