link.c

minix3.1.1源代码

/* This file handles the LINK and UNLINK system calls.  It also deals with
 * deallocating the storage used by a file when the last UNLINK is done to a
 * file and the blocks must be returned to the free block pool.
 *
 * The entry points into this file are
 *   do_link:	perform the LINK system call
 *   do_unlink:	perform the UNLINK and RMDIR system calls
 *   do_rename:	perform the RENAME system call
 *   truncate:	release all the blocks associated with an inode
 */

#include "fs.h"
#include <sys/stat.h>
#include <string.h>
#include <minix/com.h>
#include <minix/callnr.h>
#include "buf.h"
#include "file.h"
#include "fproc.h"
#include "inode.h"
#include "param.h"
#include "super.h"

#define SAME 1000

FORWARD _PROTOTYPE( int remove_dir, (struct inode *rldirp, struct inode *rip,
			char dir_name[NAME_MAX])			);

FORWARD _PROTOTYPE( int unlink_file, (struct inode *dirp, struct inode *rip,
			char file_name[NAME_MAX])			);

/*===========================================================================*
 *				do_link					     *
 *===========================================================================*/
PUBLIC int do_link()
{
/* Perform the link(name1, name2) system call. */

  register struct inode *ip, *rip;
  register int r;
  char string[NAME_MAX];
  struct inode *new_ip;

  /* See if 'name' (file to be linked) exists. */
  if (fetch_name(m_in.name1, m_in.name1_length, M1) != OK) return(err_code);
  if ( (rip = eat_path(user_path)) == NIL_INODE) return(err_code);

  /* Check to see if the file has maximum number of links already. */
  r = OK;
  if (rip->i_nlinks >= (rip->i_sp->s_version == V1 ? CHAR_MAX : SHRT_MAX))
	r = EMLINK;

  /* Only super_user may link to directories. */
  if (r == OK)
	if ( (rip->i_mode & I_TYPE) == I_DIRECTORY && !super_user) r = EPERM;

  /* If error with 'name', return the inode. */
  if (r != OK) {
	put_inode(rip);
	return(r);
  }

  /* Does the final directory of 'name2' exist? */
  if (fetch_name(m_in.name2, m_in.name2_length, M1) != OK) {
	put_inode(rip);
	return(err_code);
  }
  if ( (ip = last_dir(user_path, string)) == NIL_INODE) r = err_code;

  /* If 'name2' exists in full (even if no space) set 'r' to error. */
  if (r == OK) {
	if ( (new_ip = advance(ip, string)) == NIL_INODE) {
		r = err_code;
		if (r == ENOENT) r = OK;
	} else {
		put_inode(new_ip);
		r = EEXIST;
	}
  }

  /* Check for links across devices. */
  if (r == OK)
	if (rip->i_dev != ip->i_dev) r = EXDEV;

  /* Try to link. */
  if (r == OK)
	r = search_dir(ip, string, &rip->i_num, ENTER);

  /* If success, register the linking. */
  if (r == OK) {
	rip->i_nlinks++;
	rip->i_update |= CTIME;
	rip->i_dirt = DIRTY;
  }

  /* Done.  Release both inodes. */
  put_inode(rip);
  put_inode(ip);
  return(r);
}

/*===========================================================================*
 *				do_unlink				     *
 *===========================================================================*/
PUBLIC int do_unlink()
{
/* Perform the unlink(name) or rmdir(name) system call. The code for these two
 * is almost the same.  They differ only in some condition testing.  Unlink()
 * may be used by the superuser to do dangerous things; rmdir() may not.
 */

  register struct inode *rip;
  struct inode *rldirp;
  int r;
  char string[NAME_MAX];

  /* Get the last directory in the path. */
  if (fetch_name(m_in.name, m_in.name_length, M3) != OK) return(err_code);
  if ( (rldirp = last_dir(user_path, string)) == NIL_INODE)
	return(err_code);

  /* The last directory exists.  Does the file also exist? */
  r = OK;
  if ( (rip = advance(rldirp, string)) == NIL_INODE) r = err_code;

  /* If error, return inode. */
  if (r != OK) {
	put_inode(rldirp);
	return(r);
  }

  /* Do not remove a mount point. */
  if (rip->i_num == ROOT_INODE) {
	put_inode(rldirp);
	put_inode(rip);
	return(EBUSY);
  }

  /* Now test if the call is allowed, separately for unlink() and rmdir(). */
  if (call_nr == UNLINK) {
	/* Only the su may unlink directories, but the su can unlink any dir.*/
	if ( (rip->i_mode & I_TYPE) == I_DIRECTORY && !super_user) r = EPERM;

	/* Don't unlink a file if it is the root of a mounted file system. */
	if (rip->i_num == ROOT_INODE) r = EBUSY;

	/* Actually try to unlink the file; fails if parent is mode 0 etc. */
	if (r == OK) r = unlink_file(rldirp, rip, string);

  } else {
	r = remove_dir(rldirp, rip, string); /* call is RMDIR */
  }

  /* If unlink was possible, it has been done, otherwise it has not. */
  put_inode(rip);
  put_inode(rldirp);
  return(r);
}

/*===========================================================================*
 *				do_rename				     *
 *===========================================================================*/
PUBLIC int do_rename()
{
/* Perform the rename(name1, name2) system call. */

  struct inode *old_dirp, *old_ip;	/* ptrs to old dir, file inodes */
  struct inode *new_dirp, *new_ip;	/* ptrs to new dir, file inodes */
  struct inode *new_superdirp, *next_new_superdirp;
  int r = OK;				/* error flag; initially no error */
  int odir, ndir;			/* TRUE iff {old|new} file is dir */
  int same_pdir;			/* TRUE iff parent dirs are the same */
  char old_name[NAME_MAX], new_name[NAME_MAX];
  ino_t numb;
  int r1;
  
  /* See if 'name1' (existing file) exists.  Get dir and file inodes. */
  if (fetch_name(m_in.name1, m_in.name1_length, M1) != OK) return(err_code);
  if ( (old_dirp = last_dir(user_path, old_name))==NIL_INODE) return(err_code);

  if ( (old_ip = advance(old_dirp, old_name)) == NIL_INODE) r = err_code;

  /* See if 'name2' (new name) exists.  Get dir and file inodes. */
  if (fetch_name(m_in.name2, m_in.name2_length, M1) != OK) r = err_code;
  if ( (new_dirp = last_dir(user_path, new_name)) == NIL_INODE) r = err_code;
  new_ip = advance(new_dirp, new_name);	/* not required to exist */

  if (old_ip != NIL_INODE)
	odir = ((old_ip->i_mode & I_TYPE) == I_DIRECTORY);  /* TRUE iff dir */

  /* If it is ok, check for a variety of possible errors. */
  if (r == OK) {
	same_pdir = (old_dirp == new_dirp);

	/* The old inode must not be a superdirectory of the new last dir. */
	if (odir && !same_pdir) {
		dup_inode(new_superdirp = new_dirp);
		while (TRUE) {		/* may hang in a file system loop */
			if (new_superdirp == old_ip) {
				r = EINVAL;
				break;
			}
			next_new_superdirp = advance(new_superdirp, dot2);
			put_inode(new_superdirp);
			if (next_new_superdirp == new_superdirp)
				break;	/* back at system root directory */
			new_superdirp = next_new_superdirp;
			if (new_superdirp == NIL_INODE) {
				/* Missing ".." entry.  Assume the worst. */
				r = EINVAL;
				break;
			}
		} 	
		put_inode(new_superdirp);
	}	

	/* The old or new name must not be . or .. */
	if (strcmp(old_name, ".")==0 || strcmp(old_name, "..")==0 ||
	    strcmp(new_name, ".")==0 || strcmp(new_name, "..")==0) r = EINVAL;

	/* Both parent directories must be on the same device. */
	if (old_dirp->i_dev != new_dirp->i_dev) r = EXDEV;

	/* Parent dirs must be writable, searchable and on a writable device */
	if ((r1 = forbidden(old_dirp, W_BIT | X_BIT)) != OK ||
	    (r1 = forbidden(new_dirp, W_BIT | X_BIT)) != OK) r = r1;

	/* Some tests apply only if the new path exists. */
	if (new_ip == NIL_INODE) {
		/* don't rename a file with a file system mounted on it. */
		if (old_ip->i_dev != old_dirp->i_dev) r = EXDEV;
		if (odir && new_dirp->i_nlinks >=
		    (new_dirp->i_sp->s_version == V1 ? CHAR_MAX : SHRT_MAX) &&
		    !same_pdir && r == OK) r = EMLINK;
	} else {
		if (old_ip == new_ip) r = SAME; /* old=new */

		/* has the old file or new file a file system mounted on it? */
		if (old_ip->i_dev != new_ip->i_dev) r = EXDEV;

		ndir = ((new_ip->i_mode & I_TYPE) == I_DIRECTORY); /* dir ? */
		if (odir == TRUE && ndir == FALSE) r = ENOTDIR;
		if (odir == FALSE && ndir == TRUE) r = EISDIR;
	}
  }

  /* If a process has another root directory than the system root, we might
   * "accidently" be moving it's working directory to a place where it's
   * root directory isn't a super directory of it anymore. This can make
   * the function chroot useless. If chroot will be used often we should
   * probably check for it here.
   */

  /* The rename will probably work. Only two things can go wrong now:
   * 1. being unable to remove the new file. (when new file already exists)
   * 2. being unable to make the new directory entry. (new file doesn't exists)
   *     [directory has to grow by one block and cannot because the disk
   *      is completely full].
   */
  if (r == OK) {
	if (new_ip != NIL_INODE) {
		  /* There is already an entry for 'new'. Try to remove it. */
		if (odir) 
			r = remove_dir(new_dirp, new_ip, new_name);
		else 
			r = unlink_file(new_dirp, new_ip, new_name);
	}
	/* if r is OK, the rename will succeed, while there is now an
	 * unused entry in the new parent directory.
	 */
  }

  if (r == OK) {
	/* If the new name will be in the same parent directory as the old one,
	 * first remove the old name to free an entry for the new name,
	 * otherwise first try to create the new name entry to make sure
	 * the rename will succeed.
	 */
	numb = old_ip->i_num;		/* inode number of old file */

  	if (same_pdir) {
		r = search_dir(old_dirp, old_name, (ino_t *) 0, DELETE);
						/* shouldn't go wrong. */
		if (r==OK) (void) search_dir(old_dirp, new_name, &numb, ENTER);
	} else {
		r = search_dir(new_dirp, new_name, &numb, ENTER);
		if (r == OK)
		    (void) search_dir(old_dirp, old_name, (ino_t *) 0, DELETE);
	}
  }
  /* If r is OK, the ctime and mtime of old_dirp and new_dirp have been marked
   * for update in search_dir.
   */

  if (r == OK && odir && !same_pdir) {
	/* Update the .. entry in the directory (still points to old_dirp). */
	numb = new_dirp->i_num;
	(void) unlink_file(old_ip, NIL_INODE, dot2);
	if (search_dir(old_ip, dot2, &numb, ENTER) == OK) {
		/* New link created. */
		new_dirp->i_nlinks++;
		new_dirp->i_dirt = DIRTY;
	}
  }
	
  /* Release the inodes. */
  put_inode(old_dirp);
  put_inode(old_ip);
  put_inode(new_dirp);
  put_inode(new_ip);
  return(r == SAME ? OK : r);
}

/*===========================================================================*
 *				truncate				     *
 *===========================================================================*/
PUBLIC void truncate(rip)
register struct inode *rip;	/* pointer to inode to be truncated */
{
/* Remove all the zones from the inode 'rip' and mark it dirty. */

  register block_t b;
  zone_t z, zone_size, z1;
  off_t position;
  int i, scale, file_type, waspipe, single, nr_indirects;
  struct buf *bp;
  dev_t dev;

  file_type = rip->i_mode & I_TYPE;	/* check to see if file is special */
  if (file_type == I_CHAR_SPECIAL || file_type == I_BLOCK_SPECIAL) return;
  dev = rip->i_dev;		/* device on which inode resides */
  scale = rip->i_sp->s_log_zone_size;
  zone_size = (zone_t) rip->i_sp->s_block_size << scale;
  nr_indirects = rip->i_nindirs;

  /* Pipes can shrink, so adjust size to make sure all zones are removed. */
  waspipe = rip->i_pipe == I_PIPE;	/* TRUE is this was a pipe */
  if (waspipe) rip->i_size = PIPE_SIZE(rip->i_sp->s_block_size);

  /* Step through the file a zone at a time, finding and freeing the zones. */
  for (position = 0; position < rip->i_size; position += zone_size) {
	if ( (b = read_map(rip, position)) != NO_BLOCK) {
		z = (zone_t) b >> scale;
		free_zone(dev, z);
	}
  }

  /* All the data zones have been freed.  Now free the indirect zones. */
  rip->i_dirt = DIRTY;
  if (waspipe) {
	wipe_inode(rip);	/* clear out inode for pipes */
	return;			/* indirect slots contain file positions */
  }
  single = rip->i_ndzones;
  free_zone(dev, rip->i_zone[single]);	/* single indirect zone */
  if ( (z = rip->i_zone[single+1]) != NO_ZONE) {
	/* Free all the single indirect zones pointed to by the double. */
	b = (block_t) z << scale;
	bp = get_block(dev, b, NORMAL);	/* get double indirect zone */
	for (i = 0; i < nr_indirects; i++) {
		z1 = rd_indir(bp, i);
		free_zone(dev, z1);
	}

	/* Now free the double indirect zone itself. */
	put_block(bp, INDIRECT_BLOCK);
	free_zone(dev, z);
  }

  /* Leave zone numbers for de(1) to recover file after an unlink(2).  */
}

/*===========================================================================*
 *				remove_dir				     *
 *===========================================================================*/
PRIVATE int remove_dir(rldirp, rip, dir_name)
struct inode *rldirp;		 	/* parent directory */
struct inode *rip;			/* directory to be removed */
char dir_name[NAME_MAX];		/* name of directory to be removed */
{
  /* A directory file has to be removed. Five conditions have to met:
   * 	- The file must be a directory
   *	- The directory must be empty (except for . and ..)
   *	- The final component of the path must not be . or ..
   *	- The directory must not be the root of a mounted file system
   *	- The directory must not be anybody's root/working directory
   */

  int r;
  register struct fproc *rfp;

  /* search_dir checks that rip is a directory too. */
  if ((r = search_dir(rip, "", (ino_t *) 0, IS_EMPTY)) != OK) return r;

  if (strcmp(dir_name, ".") == 0 || strcmp(dir_name, "..") == 0)return(EINVAL);
  if (rip->i_num == ROOT_INODE) return(EBUSY); /* can't remove 'root' */
  
  for (rfp = &fproc[INIT_PROC_NR + 1]; rfp < &fproc[NR_PROCS]; rfp++)
	if (rfp->fp_workdir == rip || rfp->fp_rootdir == rip) return(EBUSY);
				/* can't remove anybody's working dir */

  /* Actually try to unlink the file; fails if parent is mode 0 etc. */
  if ((r = unlink_file(rldirp, rip, dir_name)) != OK) return r;

  /* Unlink . and .. from the dir. The super user can link and unlink any dir,
   * so don't make too many assumptions about them.
   */
  (void) unlink_file(rip, NIL_INODE, dot1);
  (void) unlink_file(rip, NIL_INODE, dot2);
  return(OK);
}

/*===========================================================================*
 *				unlink_file				     *
 *===========================================================================*/
PRIVATE int unlink_file(dirp, rip, file_name)
struct inode *dirp;		/* parent directory of file */
struct inode *rip;		/* inode of file, may be NIL_INODE too. */
char file_name[NAME_MAX];	/* name of file to be removed */
{
/* Unlink 'file_name'; rip must be the inode of 'file_name' or NIL_INODE. */

  ino_t numb;			/* inode number */
  int	r;

  /* If rip is not NIL_INODE, it is used to get faster access to the inode. */
  if (rip == NIL_INODE) {
  	/* Search for file in directory and try to get its inode. */
	err_code = search_dir(dirp, file_name, &numb, LOOK_UP);
	if (err_code == OK) rip = get_inode(dirp->i_dev, (int) numb);
	if (err_code != OK || rip == NIL_INODE) return(err_code);
  } else {
	dup_inode(rip);		/* inode will be returned with put_inode */
  }

  r = search_dir(dirp, file_name, (ino_t *) 0, DELETE);

  if (r == OK) {
	rip->i_nlinks--;	/* entry deleted from parent's dir */
	rip->i_update |= CTIME;
	rip->i_dirt = DIRTY;
  }

  put_inode(rip);
  return(r);
}