source: branches/minix3-book/servers/fs/path.c@ 12

/* This file contains the procedures that look up path names in the directory
 * system and determine the inode number that goes with a given path name.
 *
 *  The entry points into this file are
 *   eat_path:   the 'main' routine of the path-to-inode conversion mechanism
 *   last_dir:   find the final directory on a given path
 *   advance:    parse one component of a path name
 *   search_dir: search a directory for a string and return its inode number
 */

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

PUBLIC char dot1[2] = ".";      /* used for search_dir to bypass the access */
PUBLIC char dot2[3] = "..";     /* permissions for . and ..                 */

FORWARD _PROTOTYPE( char *get_name, (char *old_name, char string [NAME_MAX]) );

/*===========================================================================*
 *                              eat_path                                     *
 *===========================================================================*/
PUBLIC struct inode *eat_path(path)
char *path;                     /* the path name to be parsed */
{
/* Parse the path 'path' and put its inode in the inode table. If not possible,
 * return NIL_INODE as function value and an error code in 'err_code'.
 */

  register struct inode *ldip, *rip;
  char string[NAME_MAX];        /* hold 1 path component name here */

  /* First open the path down to the final directory. */
  if ( (ldip = last_dir(path, string)) == NIL_INODE) {
        return(NIL_INODE);      /* we couldn't open final directory */
        }

  /* The path consisting only of "/" is a special case, check for it. */
  if (string[0] == '\0') return(ldip);

  /* Get final component of the path. */
  rip = advance(ldip, string);
  put_inode(ldip);
  return(rip);
}

/*===========================================================================*
 *                              last_dir                                     *
 *===========================================================================*/
PUBLIC struct inode *last_dir(path, string)
char *path;                     /* the path name to be parsed */
char string[NAME_MAX];          /* the final component is returned here */
{
/* Given a path, 'path', located in the fs address space, parse it as
 * far as the last directory, fetch the inode for the last directory into
 * the inode table, and return a pointer to the inode.  In
 * addition, return the final component of the path in 'string'.
 * If the last directory can't be opened, return NIL_INODE and
 * the reason for failure in 'err_code'.
 */

  register struct inode *rip;
  register char *new_name;
  register struct inode *new_ip;

  /* Is the path absolute or relative?  Initialize 'rip' accordingly. */
  rip = (*path == '/' ? fp->fp_rootdir : fp->fp_workdir);

  /* If dir has been removed or path is empty, return ENOENT. */
  if (rip->i_nlinks == 0 || *path == '\0') {
        err_code = ENOENT;
        return(NIL_INODE);
  }

  dup_inode(rip);               /* inode will be returned with put_inode */

  /* Scan the path component by component. */
  while (TRUE) {
        /* Extract one component. */
        if ( (new_name = get_name(path, string)) == (char*) 0) {
                put_inode(rip); /* bad path in user space */
                return(NIL_INODE);
        }
        if (*new_name == '\0') {
                if ( (rip->i_mode & I_TYPE) == I_DIRECTORY) {
                        return(rip);    /* normal exit */
                } else {
                        /* last file of path prefix is not a directory */
                        put_inode(rip);
                        err_code = ENOTDIR;                     
                        return(NIL_INODE);
                }
        }

        /* There is more path.  Keep parsing. */
        new_ip = advance(rip, string);
        put_inode(rip);         /* rip either obsolete or irrelevant */
        if (new_ip == NIL_INODE) return(NIL_INODE);

        /* The call to advance() succeeded.  Fetch next component. */
        path = new_name;
        rip = new_ip;
  }
}

/*===========================================================================*
 *                              get_name                                     *
 *===========================================================================*/
PRIVATE char *get_name(old_name, string)
char *old_name;                 /* path name to parse */
char string[NAME_MAX];          /* component extracted from 'old_name' */
{
/* Given a pointer to a path name in fs space, 'old_name', copy the next
 * component to 'string' and pad with zeros.  A pointer to that part of
 * the name as yet unparsed is returned.  Roughly speaking,
 * 'get_name' = 'old_name' - 'string'.
 *
 * This routine follows the standard convention that /usr/ast, /usr//ast,
 * //usr///ast and /usr/ast/ are all equivalent.
 */

  register int c;
  register char *np, *rnp;

  np = string;                  /* 'np' points to current position */
  rnp = old_name;               /* 'rnp' points to unparsed string */
  while ( (c = *rnp) == '/') rnp++;     /* skip leading slashes */

  /* Copy the unparsed path, 'old_name', to the array, 'string'. */
  while ( rnp < &old_name[PATH_MAX]  &&  c != '/'   &&  c != '\0') {
        if (np < &string[NAME_MAX]) *np++ = c;
        c = *++rnp;             /* advance to next character */
  }

  /* To make /usr/ast/ equivalent to /usr/ast, skip trailing slashes. */
  while (c == '/' && rnp < &old_name[PATH_MAX]) c = *++rnp;

  if (np < &string[NAME_MAX]) *np = '\0';       /* Terminate string */

  if (rnp >= &old_name[PATH_MAX]) {
        err_code = ENAMETOOLONG;
        return((char *) 0);
  }
  return(rnp);
}

/*===========================================================================*
 *                              advance                                      *
 *===========================================================================*/
PUBLIC struct inode *advance(dirp, string)
struct inode *dirp;             /* inode for directory to be searched */
char string[NAME_MAX];          /* component name to look for */
{
/* Given a directory and a component of a path, look up the component in
 * the directory, find the inode, open it, and return a pointer to its inode
 * slot.  If it can't be done, return NIL_INODE.
 */

  register struct inode *rip;
  struct inode *rip2;
  register struct super_block *sp;
  int r, inumb;
  dev_t mnt_dev;
  ino_t numb;

  /* If 'string' is empty, yield same inode straight away. */
  if (string[0] == '\0') { return(get_inode(dirp->i_dev, (int) dirp->i_num)); }

  /* Check for NIL_INODE. */
  if (dirp == NIL_INODE) { return(NIL_INODE); }

  /* If 'string' is not present in the directory, signal error. */
  if ( (r = search_dir(dirp, string, &numb, LOOK_UP)) != OK) {
        err_code = r;
        return(NIL_INODE);
  }

  /* Don't go beyond the current root directory, unless the string is dot2. */
  if (dirp == fp->fp_rootdir && strcmp(string, "..") == 0 && string != dot2)
                return(get_inode(dirp->i_dev, (int) dirp->i_num));

  /* The component has been found in the directory.  Get inode. */
  if ( (rip = get_inode(dirp->i_dev, (int) numb)) == NIL_INODE)  {
        return(NIL_INODE);
        }

  if (rip->i_num == ROOT_INODE)
        if (dirp->i_num == ROOT_INODE) {
            if (string[1] == '.') {
                for (sp = &super_block[1]; sp < &super_block[NR_SUPERS]; sp++){
                        if (sp->s_dev == rip->i_dev) {
                                /* Release the root inode.  Replace by the
                                 * inode mounted on.
                                 */
                                put_inode(rip);
                                mnt_dev = sp->s_imount->i_dev;
                                inumb = (int) sp->s_imount->i_num;
                                rip2 = get_inode(mnt_dev, inumb);
                                rip = advance(rip2, string);
                                put_inode(rip2);
                                break;
                        }
                }
            }
        }
  if (rip == NIL_INODE) return(NIL_INODE);

  /* See if the inode is mounted on.  If so, switch to root directory of the
   * mounted file system.  The super_block provides the linkage between the
   * inode mounted on and the root directory of the mounted file system.
   */
  while (rip != NIL_INODE && rip->i_mount == I_MOUNT) {
        /* The inode is indeed mounted on. */
        for (sp = &super_block[0]; sp < &super_block[NR_SUPERS]; sp++) {
                if (sp->s_imount == rip) {
                        /* Release the inode mounted on.  Replace by the
                         * inode of the root inode of the mounted device.
                         */
                        put_inode(rip);
                        rip = get_inode(sp->s_dev, ROOT_INODE);
                        break;
                }
        }
  }
  return(rip);          /* return pointer to inode's component */
}

/*===========================================================================*
 *                              search_dir                                   *
 *===========================================================================*/
PUBLIC int search_dir(ldir_ptr, string, numb, flag)
register struct inode *ldir_ptr; /* ptr to inode for dir to search */
char string[NAME_MAX];           /* component to search for */
ino_t *numb;                     /* pointer to inode number */
int flag;                        /* LOOK_UP, ENTER, DELETE or IS_EMPTY */
{
/* This function searches the directory whose inode is pointed to by 'ldip':
 * if (flag == ENTER)  enter 'string' in the directory with inode # '*numb';
 * if (flag == DELETE) delete 'string' from the directory;
 * if (flag == LOOK_UP) search for 'string' and return inode # in 'numb';
 * if (flag == IS_EMPTY) return OK if only . and .. in dir else ENOTEMPTY;
 *
 *    if 'string' is dot1 or dot2, no access permissions are checked.
 */

  register struct direct *dp = NULL;
  register struct buf *bp = NULL;
  int i, r, e_hit, t, match;
  mode_t bits;
  off_t pos;
  unsigned new_slots, old_slots;
  block_t b;
  struct super_block *sp;
  int extended = 0;

  /* If 'ldir_ptr' is not a pointer to a dir inode, error. */
  if ( (ldir_ptr->i_mode & I_TYPE) != I_DIRECTORY) return(ENOTDIR);

  r = OK;

  if (flag != IS_EMPTY) {
        bits = (flag == LOOK_UP ? X_BIT : W_BIT | X_BIT);

        if (string == dot1 || string == dot2) {
                if (flag != LOOK_UP) r = read_only(ldir_ptr);
                                     /* only a writable device is required. */
        }
        else r = forbidden(ldir_ptr, bits); /* check access permissions */
  }
  if (r != OK) return(r);
  
  /* Step through the directory one block at a time. */
  old_slots = (unsigned) (ldir_ptr->i_size/DIR_ENTRY_SIZE);
  new_slots = 0;
  e_hit = FALSE;
  match = 0;                    /* set when a string match occurs */

  for (pos = 0; pos < ldir_ptr->i_size; pos += ldir_ptr->i_sp->s_block_size) {
        b = read_map(ldir_ptr, pos);    /* get block number */

        /* Since directories don't have holes, 'b' cannot be NO_BLOCK. */
        bp = get_block(ldir_ptr->i_dev, b, NORMAL);     /* get a dir block */

        if (bp == NO_BLOCK)
                panic(__FILE__,"get_block returned NO_BLOCK", NO_NUM);

        /* Search a directory block. */
        for (dp = &bp->b_dir[0];
                dp < &bp->b_dir[NR_DIR_ENTRIES(ldir_ptr->i_sp->s_block_size)];
                dp++) {
                if (++new_slots > old_slots) { /* not found, but room left */
                        if (flag == ENTER) e_hit = TRUE;
                        break;
                }

                /* Match occurs if string found. */
                if (flag != ENTER && dp->d_ino != 0) {
                        if (flag == IS_EMPTY) {
                                /* If this test succeeds, dir is not empty. */
                                if (strcmp(dp->d_name, "." ) != 0 &&
                                    strcmp(dp->d_name, "..") != 0) match = 1;
                        } else {
                                if (strncmp(dp->d_name, string, NAME_MAX) == 0) {
                                        match = 1;
                                }
                        }
                }

                if (match) {
                        /* LOOK_UP or DELETE found what it wanted. */
                        r = OK;
                        if (flag == IS_EMPTY) r = ENOTEMPTY;
                        else if (flag == DELETE) {
                                /* Save d_ino for recovery. */
                                t = NAME_MAX - sizeof(ino_t);
                                *((ino_t *) &dp->d_name[t]) = dp->d_ino;
                                dp->d_ino = 0;  /* erase entry */
                                bp->b_dirt = DIRTY;
                                ldir_ptr->i_update |= CTIME | MTIME;
                                ldir_ptr->i_dirt = DIRTY;
                        } else {
                                sp = ldir_ptr->i_sp;    /* 'flag' is LOOK_UP */
                                *numb = conv4(sp->s_native, (int) dp->d_ino);
                        }
                        put_block(bp, DIRECTORY_BLOCK);
                        return(r);
                }

                /* Check for free slot for the benefit of ENTER. */
                if (flag == ENTER && dp->d_ino == 0) {
                        e_hit = TRUE;   /* we found a free slot */
                        break;
                }
        }

        /* The whole block has been searched or ENTER has a free slot. */
        if (e_hit) break;       /* e_hit set if ENTER can be performed now */
        put_block(bp, DIRECTORY_BLOCK); /* otherwise, continue searching dir */
  }

  /* The whole directory has now been searched. */
  if (flag != ENTER) {
        return(flag == IS_EMPTY ? OK : ENOENT);
  }

  /* This call is for ENTER.  If no free slot has been found so far, try to
   * extend directory.
   */
  if (e_hit == FALSE) { /* directory is full and no room left in last block */
        new_slots++;            /* increase directory size by 1 entry */
        if (new_slots == 0) return(EFBIG); /* dir size limited by slot count */
        if ( (bp = new_block(ldir_ptr, ldir_ptr->i_size)) == NIL_BUF)
                return(err_code);
        dp = &bp->b_dir[0];
        extended = 1;
  }

  /* 'bp' now points to a directory block with space. 'dp' points to slot. */
  (void) memset(dp->d_name, 0, (size_t) NAME_MAX); /* clear entry */
  for (i = 0; string[i] && i < NAME_MAX; i++) dp->d_name[i] = string[i];
  sp = ldir_ptr->i_sp; 
  dp->d_ino = conv4(sp->s_native, (int) *numb);
  bp->b_dirt = DIRTY;
  put_block(bp, DIRECTORY_BLOCK);
  ldir_ptr->i_update |= CTIME | MTIME;  /* mark mtime for update later */
  ldir_ptr->i_dirt = DIRTY;
  if (new_slots > old_slots) {
        ldir_ptr->i_size = (off_t) new_slots * DIR_ENTRY_SIZE;
        /* Send the change to disk if the directory is extended. */
        if (extended) rw_inode(ldir_ptr, WRITING);
  }
  return(OK);
}