sysfile.c

//
// File-system system calls.
// Mostly argument checking, since we don't trust
// user code, and calls into file.c and fs.c.
//

#include "types.h"
#include "defs.h"
#include "param.h"
#include "stat.h"
#include "mmu.h"
#include "proc.h"
#include "fs.h"
#include "spinlock.h"
#include "sleeplock.h"
#include "file.h"
#include "fcntl.h"

// Fetch the nth word-sized system call argument as a file descriptor
// and return both the descriptor and the corresponding struct file.
static int argfd(int n, int *pfd, struct file **pf) {
  int fd;
  struct file *f;

  if (argint(n, &fd) < 0)
    return -1;
  if (fd < 0 || fd >= NOFILE || (f = myproc()->ofile[fd]) == 0)
    return -1;
  if (pfd)
    *pfd = fd;
  if (pf)
    *pf = f;
  return 0;
}

// Allocate a file descriptor for the given file.
// Takes over file reference from caller on success.
static int fdalloc(struct file *f) {
  int fd;
  struct proc *curproc = myproc();

  for (fd = 0; fd < NOFILE; fd++) {
    if (curproc->ofile[fd] == 0) {
      curproc->ofile[fd] = f;
      return fd;
    }
  }
  return -1;
}

int sys_dup(void) {
  struct file *f;
  int fd;

  if (argfd(0, 0, &f) < 0)
    return -1;
  if ((fd = fdalloc(f)) < 0)
    return -1;
  filedup(f);
  return fd;
}

int sys_read(void) {
  struct file *f;
  int n;
  char *p;

  if (argfd(0, 0, &f) < 0 || argint(2, &n) < 0 || argptr(1, &p, n) < 0)
    return -1;
  return fileread(f, p, n);
}

int sys_write(void) {
  struct file *f;
  int n;
  char *p;

  if (argfd(0, 0, &f) < 0 || argint(2, &n) < 0 || argptr(1, &p, n) < 0)
    return -1;
  return filewrite(f, p, n);
}

int sys_close(void) {
  int fd;
  struct file *f;

  if (argfd(0, &fd, &f) < 0)
    return -1;
  myproc()->ofile[fd] = 0;
  fileclose(f);
  return 0;
}

int sys_fstat(void) {
  struct file *f;
  struct stat *st;

  if (argfd(0, 0, &f) < 0 || argptr(1, (void *)&st, sizeof(*st)) < 0)
    return -1;
  return filestat(f, st);
}

// Create the path new as a link to the same inode as old.
int sys_link(void) {
  char name[DIRSIZ], *new, *old;
  struct inode *dp, *ip;

  if (argstr(0, &old) < 0 || argstr(1, &new) < 0)
    return -1;

  begin_op();
  if ((ip = namei(old)) == 0) {
    end_op();
    return -1;
  }

  ilock(ip);
  if (ip->type == T_DIR) {
    iunlockput(ip);
    end_op();
    return -1;
  }

  ip->nlink++;
  iupdate(ip);
  iunlock(ip);

  if ((dp = nameiparent(new, name)) == 0)
    goto bad;
  ilock(dp);
  if (dp->dev != ip->dev || dirlink(dp, name, ip->inum) < 0) {
    iunlockput(dp);
    goto bad;
  }
  iunlockput(dp);
  iput(ip);

  end_op();

  return 0;

bad:
  ilock(ip);
  ip->nlink--;
  iupdate(ip);
  iunlockput(ip);
  end_op();
  return -1;
}

// Is the directory dp empty except for "." and ".." ?
static int isdirempty(struct inode *dp) {
  int off;
  struct dirent de;

  for (off = 2 * sizeof(de); off < dp->size; off += sizeof(de)) {
    if (readi(dp, (char *)&de, off, sizeof(de)) != sizeof(de))
      panic("isdirempty: readi");
    if (de.inum != 0)
      return 0;
  }
  return 1;
}

// PAGEBREAK!
int sys_unlink(void) {
  struct inode *ip, *dp;
  struct dirent de;
  char name[DIRSIZ], *path;
  uint off;

  if (argstr(0, &path) < 0)
    return -1;

  begin_op();
  if ((dp = nameiparent(path, name)) == 0) {
    end_op();
    return -1;
  }

  ilock(dp);

  // Cannot unlink "." or "..".
  if (namecmp(name, ".") == 0 || namecmp(name, "..") == 0)
    goto bad;

  if ((ip = dirlookup(dp, name, &off)) == 0)
    goto bad;
  ilock(ip);

  if (ip->nlink < 1)
    panic("unlink: nlink < 1");
  if (ip->type == T_DIR && !isdirempty(ip)) {
    iunlockput(ip);
    goto bad;
  }

  memset(&de, 0, sizeof(de));
  if (writei(dp, (char *)&de, off, sizeof(de)) != sizeof(de))
    panic("unlink: writei");
  if (ip->type == T_DIR) {
    dp->nlink--;
    iupdate(dp);
  }
  iunlockput(dp);

  ip->nlink--;
  iupdate(ip);
  iunlockput(ip);

  end_op();

  return 0;

bad:
  iunlockput(dp);
  end_op();
  return -1;
}

static struct inode *create(char *path, short type, short major, short minor) {
  struct inode *ip, *dp;
  char name[DIRSIZ];

  if ((dp = nameiparent(path, name)) == 0)
    return 0;
  ilock(dp);

  if ((ip = dirlookup(dp, name, 0)) != 0) {
    iunlockput(dp);
    ilock(ip);
    if (type == T_FILE && ip->type == T_FILE)
      return ip;
    iunlockput(ip);
    return 0;
  }

  if ((ip = ialloc(dp->dev, type)) == 0)
    panic("create: ialloc");

  ilock(ip);
  ip->major = major;
  ip->minor = minor;
  ip->nlink = 1;
  iupdate(ip);

  if (type == T_DIR) { // Create . and .. entries.
    dp->nlink++;       // for ".."
    iupdate(dp);
    // No ip->nlink++ for ".": avoid cyclic ref count.
    if (dirlink(ip, ".", ip->inum) < 0 || dirlink(ip, "..", dp->inum) < 0)
      panic("create dots");
  }

  if (dirlink(dp, name, ip->inum) < 0)
    panic("create: dirlink");

  iunlockput(dp);

  return ip;
}

int sys_open(void) {
  char *path;
  int fd, omode;
  struct file *f;
  struct inode *ip;

  if (argstr(0, &path) < 0 || argint(1, &omode) < 0)
    return -1;

  begin_op();

  if (omode & O_CREATE) {
    ip = create(path, T_FILE, 0, 0);
    if (ip == 0) {
      end_op();
      return -1;
    }
  } else {
    if ((ip = namei(path)) == 0) {
      end_op();
      return -1;
    }
    ilock(ip);
    if (ip->type == T_DIR && omode != O_RDONLY) {
      iunlockput(ip);
      end_op();
      return -1;
    }
  }

  if ((f = filealloc()) == 0 || (fd = fdalloc(f)) < 0) {
    if (f)
      fileclose(f);
    iunlockput(ip);
    end_op();
    return -1;
  }
  iunlock(ip);
  end_op();

  f->type = FD_INODE;
  f->ip = ip;
  f->off = 0;
  f->readable = !(omode & O_WRONLY);
  f->writable = (omode & O_WRONLY) || (omode & O_RDWR);
  return fd;
}

int sys_mkdir(void) {
  char *path;
  struct inode *ip;

  begin_op();
  if (argstr(0, &path) < 0 || (ip = create(path, T_DIR, 0, 0)) == 0) {
    end_op();
    return -1;
  }
  iunlockput(ip);
  end_op();
  return 0;
}

int sys_mknod(void) {
  struct inode *ip;
  char *path;
  int major, minor;

  begin_op();
  if ((argstr(0, &path)) < 0 || argint(1, &major) < 0 ||
      argint(2, &minor) < 0 || (ip = create(path, T_DEV, major, minor)) == 0) {
    end_op();
    return -1;
  }
  iunlockput(ip);
  end_op();
  return 0;
}

int sys_chdir(void) {
  char *path;
  struct inode *ip;
  struct proc *curproc = myproc();

  begin_op();
  if (argstr(0, &path) < 0 || (ip = namei(path)) == 0) {
    end_op();
    return -1;
  }
  ilock(ip);
  if (ip->type != T_DIR) {
    iunlockput(ip);
    end_op();
    return -1;
  }
  iunlock(ip);
  iput(curproc->cwd);
  end_op();
  curproc->cwd = ip;
  return 0;
}

int sys_exec(void) {
  char *path, *argv[MAXARG];
  int i;
  uint uargv, uarg;

  if (argstr(0, &path) < 0 || argint(1, (int *)&uargv) < 0) {
    return -1;
  }
  memset(argv, 0, sizeof(argv));
  for (i = 0;; i++) {
    if (i >= NELEM(argv))
      return -1;
    if (fetchint(uargv + 4 * i, (int *)&uarg) < 0)
      return -1;
    if (uarg == 0) {
      argv[i] = 0;
      break;
    }
    if (fetchstr(uarg, &argv[i]) < 0)
      return -1;
  }
  return exec(path, argv);
}

int sys_pipe(void) {
  int *fd;
  struct file *rf, *wf;
  int fd0, fd1;

  if (argptr(0, (void *)&fd, 2 * sizeof(fd[0])) < 0)
    return -1;
  if (pipealloc(&rf, &wf) < 0)
    return -1;
  fd0 = -1;
  if ((fd0 = fdalloc(rf)) < 0 || (fd1 = fdalloc(wf)) < 0) {
    if (fd0 >= 0)
      myproc()->ofile[fd0] = 0;
    fileclose(rf);
    fileclose(wf);
    return -1;
  }
  fd[0] = fd0;
  fd[1] = fd1;
  return 0;
}