panic() cleanup.

[minix.git] / servers / mfs / path.c

/* 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 <minix/endpoint.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include "buf.h"
#include "inode.h"
#include "super.h"
#include <minix/vfsif.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 *name, char string[NAME_MAX+1]) );
FORWARD _PROTOTYPE( int ltraverse, (struct inode *rip, char *suffix)    );
FORWARD _PROTOTYPE( int parse_path, (ino_t dir_ino, ino_t root_ino,
                                        int flags, struct inode **res_inop,
                                        size_t *offsetp, int *symlinkp) );


/*===========================================================================*
 *                             fs_lookup                                     *
 *===========================================================================*/
PUBLIC int fs_lookup()
{
  cp_grant_id_t grant, grant2;
  int r, r1, len, flags, symlinks;
  size_t offset = 0, path_size, cred_size;
  ino_t dir_ino, root_ino;
  struct inode *rip;

  grant         = fs_m_in.REQ_GRANT;
  path_size     = fs_m_in.REQ_PATH_SIZE;        /* Size of the buffer */
  len           = fs_m_in.REQ_PATH_LEN; /* including terminating nul */
  dir_ino       = fs_m_in.REQ_DIR_INO;
  root_ino      = fs_m_in.REQ_ROOT_INO;
  flags         = fs_m_in.REQ_FLAGS;

  /* Check length. */
  if(len > sizeof(user_path)) return(E2BIG);    /* too big for buffer */
  if(len < 1) return(EINVAL);                   /* too small */

  /* Copy the pathname and set up caller's user and group id */
  r = sys_safecopyfrom(FS_PROC_NR, grant, /*offset*/ 0, 
            (vir_bytes) user_path, (phys_bytes) len, D);
  if(r != OK) {
        printf("MFS %s:%d sys_safecopyfrom failed: %d\n", 
               __FILE__, __LINE__, r);
        return(r);
  }

  /* Verify this is a null-terminated path. */
  if(user_path[len - 1] != '\0') return(EINVAL);

  if(flags & PATH_GET_UCRED) { /* Do we have to copy uid/gid credentials? */
        int i;
        grant2  = fs_m_in.REQ_GRANT2;
        cred_size = fs_m_in.REQ_UCRED_SIZE;

        if (cred_size > sizeof(credentials)) return(EINVAL); /* Too big. */
        r = sys_safecopyfrom(FS_PROC_NR, grant2, 0, (vir_bytes) &credentials,
                             (phys_bytes) cred_size, D);
        if (r != OK) {
                printf("MFS %s:%d sys_safecopyfrom failed: %d\n",
                       __FILE__, __LINE__, r);
                return(r);
        }
        caller_uid = credentials.vu_uid;
        caller_gid = credentials.vu_gid;
  } else {
        memset(&credentials, 0, sizeof(credentials));
        caller_uid      = fs_m_in.REQ_UID;
        caller_gid      = fs_m_in.REQ_GID;
  }

  /* Lookup inode */
  rip = NULL;
  r = parse_path(dir_ino, root_ino, flags, &rip, &offset, &symlinks);

  if(symlinks != 0 && (r == ELEAVEMOUNT || r == EENTERMOUNT || r == ESYMLINK)){
        len = strlen(user_path)+1;
        if(len > path_size) return(ENAMETOOLONG);

        r1 = sys_safecopyto(FS_PROC_NR, grant, 0, (vir_bytes) user_path,
                            (phys_bytes) len, D);
        if(r1 != OK) {
                printf("%s:%d fs_lookup: sys_safecopyto failed: %d\n",
                       __FILE__, __LINE__, r1);
                return(r1);
        }
  }

  if(r == ELEAVEMOUNT || r == ESYMLINK) {
          /* Report offset and the error */
          fs_m_out.RES_OFFSET = offset;
          fs_m_out.RES_SYMLOOP = symlinks;

          return(r);
  }

  if (r != OK && r != EENTERMOUNT) return(r);

  fs_m_out.RES_INODE_NR = rip->i_num;
  fs_m_out.RES_MODE             = rip->i_mode;
  fs_m_out.RES_FILE_SIZE_LO     = rip->i_size;
  fs_m_out.RES_SYMLOOP          = symlinks;
  fs_m_out.RES_UID              = rip->i_uid;
  fs_m_out.RES_GID              = rip->i_gid;
  
  /* This is only valid for block and character specials. But it doesn't
   * cause any harm to set RES_DEV always. */
  fs_m_out.RES_DEV              = (dev_t) rip->i_zone[0];

  if(r == EENTERMOUNT) {
          fs_m_out.RES_OFFSET   = offset;
          put_inode(rip); /* Only return a reference to the final object */
  }

  return(r);
}


/*===========================================================================*
 *                             parse_path                                    *
 *===========================================================================*/
PRIVATE int parse_path(dir_ino, root_ino, flags, res_inop, offsetp, symlinkp)
ino_t dir_ino;
ino_t root_ino;
int flags;
struct inode **res_inop;
size_t *offsetp;
int *symlinkp;
{
  /* Parse the path in user_path, starting at dir_ino. If the path is the empty
   * string, just return dir_ino. It is upto the caller to treat an empty
   * path in a special way. Otherwise, if the path consists of just one or
   * more slash ('/') characters, the path is replaced with ".". Otherwise,
   * just look up the first (or only) component in path after skipping any
   * leading slashes. 
   */
  int r, leaving_mount;
  struct inode *rip, *dir_ip;
  char *cp, *next_cp; /* component and next component */
  char component[NAME_MAX+1];

  /* Start parsing path at the first component in user_path */
  cp = user_path;  

  /* No symlinks encountered yet */
  *symlinkp = 0;

  /* Find starting inode inode according to the request message */
  if((rip = find_inode(fs_dev, dir_ino)) == NIL_INODE) 
        return(ENOENT);

  /* If dir has been removed return ENOENT. */
  if (rip->i_nlinks == 0) 
        return(ENOENT);
 
  dup_inode(rip);

  /* If the given start inode is a mountpoint, we must be here because the file
   * system mounted on top returned an ELEAVEMOUNT error. In this case, we must
   * only accept ".." as the first path component.
   */
  leaving_mount = rip->i_mountpoint; /* True iff rip is a mountpoint */

  /* Scan the path component by component. */
  while (TRUE) {
        if(cp[0] == '\0') {
                /* We're done; either the path was empty or we've parsed all 
                   components of the path */
                
                *res_inop = rip;
                *offsetp += cp - user_path;

                /* Return EENTERMOUNT if we are at a mount point */
                if (rip->i_mountpoint) return(EENTERMOUNT);
                
                return(OK);
        }

        while(cp[0] == '/') cp++;
        next_cp = get_name(cp, component);

        /* Special code for '..'. A process is not allowed to leave a chrooted
         * environment. A lookup of '..' at the root of a mounted filesystem
         * has to return ELEAVEMOUNT. In both cases, the caller needs search
         * permission for the current inode, as it is used as directory.
         */
        if(strcmp(component, "..") == 0) {
                /* 'rip' is now accessed as directory */
                if ((r = forbidden(rip, X_BIT)) != OK) {
                        put_inode(rip);
                        return(r);
                }

                if (rip->i_num == root_ino) {
                        cp = next_cp;
                        continue;       /* Ignore the '..' at a process' root 
                                           and move on to the next component */
                }
                
                if (rip->i_num == ROOT_INODE && !rip->i_sp->s_is_root) {
                        /* Climbing up to parent FS */

                        put_inode(rip);
                        *offsetp += cp - user_path; 
                        return(ELEAVEMOUNT);
                }
        }

        /* Only check for a mount point if we are not coming from one. */
        if (!leaving_mount && rip->i_mountpoint) {
                /* Going to enter a child FS */

                *res_inop = rip;
                *offsetp += cp - user_path;
                return(EENTERMOUNT);
        }

        /* There is more path.  Keep parsing.
         * If we're leaving a mountpoint, skip directory permission checks.
         */
        dir_ip = rip;
        rip = advance(dir_ip, leaving_mount ? dot2 : component, CHK_PERM);
        if(err_code == ELEAVEMOUNT || err_code == EENTERMOUNT)
                err_code = OK;

        if (err_code != OK) {
                put_inode(dir_ip);
                return(err_code);
        }
        
        leaving_mount = 0;

        /* The call to advance() succeeded.  Fetch next component. */
        if (S_ISLNK(rip->i_mode)) {

                if (next_cp[0] == '\0' && (flags & PATH_RET_SYMLINK)) {
                        put_inode(dir_ip);
                        *res_inop = rip;
                        *offsetp += next_cp - user_path;
                        return(OK);
                }

                /* Extract path name from the symlink file */
                r = ltraverse(rip, next_cp);
                next_cp = user_path;
                *offsetp = 0;

                /* Symloop limit reached? */
                if (++(*symlinkp) > SYMLOOP_MAX)
                        r = ELOOP;

                if (r != OK) {
                        put_inode(dir_ip);
                        put_inode(rip);
                        return(r);
                }

                if (next_cp[0] == '/') {
                        put_inode(dir_ip);
                        put_inode(rip);
                        return(ESYMLINK);
                }
        
                put_inode(rip);
                dup_inode(dir_ip);
                rip = dir_ip;
        } 

        put_inode(dir_ip);
        cp = next_cp; /* Process subsequent component in next round */
  }
}


/*===========================================================================*
 *                             ltraverse                                     *
 *===========================================================================*/
PRIVATE int ltraverse(rip, suffix)
register struct inode *rip;     /* symbolic link */
char *suffix;                   /* current remaining path. Has to point in the
                                 * user_path buffer
                                 */
{
/* Traverse a symbolic link. Copy the link text from the inode and insert
 * the text into the path. Return error code or report success. Base 
 * directory has to be determined according to the first character of the
 * new pathname.
 */
  
  block_t blink;        /* block containing link text */
  size_t llen;          /* length of link */
  size_t slen;          /* length of suffix */
  struct buf *bp;       /* buffer containing link text */
  char *sp;             /* start of link text */

  bp  = NIL_BUF;

  if ((blink = read_map(rip, (off_t) 0)) == NO_BLOCK)
        return(EIO);

  bp = get_block(rip->i_dev, blink, NORMAL);
  llen = rip->i_size;
  sp = bp->b_data;
  slen = strlen(suffix);

  /* The path we're parsing looks like this:
   * /already/processed/path/<link> or
   * /already/processed/path/<link>/not/yet/processed/path
   * After expanding the <link>, the path will look like
   * <expandedlink> or
   * <expandedlink>/not/yet/processed
   * In both cases user_path must have enough room to hold <expandedlink>.
   * However, in the latter case we have to move /not/yet/processed to the
   * right place first, before we expand <link>. When strlen(<expandedlink>) is
   * smaller than strlen(/already/processes/path), we move the suffix to the
   * left. Is strlen(<expandedlink>) greater then we move it to the right. Else
   * we do nothing. */ 

  if (slen > 0) { /* Do we have path after the link? */
        /* For simplicity we require that suffix starts with a slash */
        if (suffix[0] != '/') {
                panic("ltraverse: suffix does not start with a slash");
        }

        /* To be able to expand the <link>, we have to move the 'suffix'
         * to the right place. */
        if (slen + llen + 1 > sizeof(user_path))
                return(ENAMETOOLONG);/* <expandedlink>+suffix+\0 does not fit*/
        if (suffix-user_path != llen) /* Move suffix left or right if needed */
                memmove(&user_path[llen], suffix, slen+1);
  } else {
        if (llen + 1 > sizeof(user_path))
                return(ENAMETOOLONG); /* <expandedlink> + \0 does not fix */
                
        /* Set terminating nul */
        user_path[llen]= '\0';
  }

  /* Everything is set, now copy the expanded link to user_path */
  memmove(user_path, sp, llen);

  put_block(bp, DIRECTORY_BLOCK);
  return(OK);
}


/*===========================================================================*
 *                              advance                                      *
 *===========================================================================*/
PUBLIC struct inode *advance(dirp, string, chk_perm)
struct inode *dirp;             /* inode for directory to be searched */
char string[NAME_MAX];          /* component name to look for */
int chk_perm;                   /* check permissions when string is looked up*/
{
/* 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.
 */
  ino_t numb;
  struct inode *rip;

  /* If 'string' is empty, return an error. */
  if (string[0] == '\0') {
        err_code = ENOENT;
        return(NIL_INODE);
  }

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

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

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

  /* The following test is for "mountpoint/.." where mountpoint is a
   * mountpoint. ".." will refer to the root of the mounted filesystem,
   * but has to become a reference to the parent of the 'mountpoint'
   * directory.
   *
   * This case is recognized by the looked up name pointing to a
   * root inode, and the directory in which it is held being a
   * root inode, _and_ the name[1] being '.'. (This is a test for '..'
   * and excludes '.'.)
   */
  if (rip->i_num == ROOT_INODE) {
          if (dirp->i_num == ROOT_INODE) {
                  if (string[1] == '.') {
                          if (!rip->i_sp->s_is_root) {
                                  /* Climbing up mountpoint */
                                  err_code = ELEAVEMOUNT;
                          }
                  }
          }
  }

  /* 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.
   */
  if (rip != NIL_INODE && rip->i_mountpoint) {
          /* Mountpoint encountered, report it */
          err_code = EENTERMOUNT;
  }

  return(rip);
}


/*===========================================================================*
 *                              get_name                                     *
 *===========================================================================*/
PRIVATE char *get_name(path_name, string)
char *path_name;                /* path name to parse */
char string[NAME_MAX+1];        /* component extracted from 'old_name' */
{
/* Given a pointer to a path name in fs space, 'path_name', copy the first
 * component to 'string' (truncated if necessary, always nul terminated).
 * A pointer to the string after the first component of the name as yet
 * unparsed is returned.  Roughly speaking,
 * 'get_name' = 'path_name' - 'string'.
 *
 * This routine follows the standard convention that /usr/ast, /usr//ast,
 * //usr///ast and /usr/ast/ are all equivalent.
 */
  size_t len;
  char *cp, *ep;

  cp = path_name;

  /* Skip leading slashes */
  while (cp[0] == '/') cp++;

  /* Find the end of the first component */
  ep = cp;
  while(ep[0] != '\0' && ep[0] != '/')
        ep++;

  len = ep - cp;

  /* Truncate the amount to be copied if it exceeds NAME_MAX */
  if (len > NAME_MAX)
        len = NAME_MAX;

  /* Special case of the string at cp is empty */
  if (len == 0) 
        strcpy(string, ".");  /* Return "." */
  else {
        memcpy(string, cp, len);
        string[len]= '\0';
  }

  return(ep);
}


/*===========================================================================*
 *                              search_dir                                   *
 *===========================================================================*/
PUBLIC int search_dir(ldir_ptr, string, numb, flag, check_permissions)
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 */
int check_permissions;           /* check permissions when flag is !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 if(check_permissions) {
                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("get_block returned NO_BLOCK");

        /* 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; i < NAME_MAX && string[i]; 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);
}