minor fixes for safecopy & safemap tests

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

/* lookup() is the main routine that controls the path name lookup. It
 * handles mountpoints and symbolic links. The actual lookup requests
 * are sent through the req_lookup wrapper function.
 */

#include "fs.h"
#include <string.h>
#include <minix/callnr.h>
#include <minix/com.h>
#include <minix/keymap.h>
#include <minix/const.h>
#include <minix/endpoint.h>
#include <stddef.h>
#include <unistd.h>
#include <assert.h>
#include <minix/vfsif.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <dirent.h>
#include "threads.h"
#include "vmnt.h"
#include "vnode.h"
#include "path.h"
#include "fproc.h"
#include "param.h"

/* Set to following define to 1 if you really want to use the POSIX definition
 * (IEEE Std 1003.1, 2004) of pathname resolution. POSIX requires pathnames
 * with a traling slash (and that do not entirely consist of slash characters)
 * to be treated as if a single dot is appended. This means that for example
 * mkdir("dir/", ...) and rmdir("dir/") will fail because the call tries to
 * create or remove the directory '.'. Historically, Unix systems just ignore
 * trailing slashes.
 */
#define DO_POSIX_PATHNAME_RES   0

static int lookup(struct vnode *dirp, struct lookup *resolve,
        node_details_t *node, struct fproc *rfp);
static int check_perms(endpoint_t ep, cp_grant_id_t io_gr, size_t
        pathlen);

/*===========================================================================*
 *                              advance                                      *
 *===========================================================================*/
struct vnode *advance(dirp, resolve, rfp)
struct vnode *dirp;
struct lookup *resolve;
struct fproc *rfp;
{
/* Resolve a path name starting at dirp to a vnode. */
  int r;
  int do_downgrade = 1;
  struct vnode *new_vp, *vp;
  struct vmnt *vmp;
  struct node_details res = {0,0,0,0,0,0,0};
  tll_access_t initial_locktype;

  assert(dirp);
  assert(resolve->l_vnode_lock != TLL_NONE);
  assert(resolve->l_vmnt_lock != TLL_NONE);

  if (resolve->l_vnode_lock == VNODE_READ)
        initial_locktype = VNODE_OPCL;
  else
        initial_locktype = resolve->l_vnode_lock;

  /* Get a free vnode and lock it */
  if ((new_vp = get_free_vnode()) == NULL) return(NULL);
  lock_vnode(new_vp, initial_locktype);

  /* Lookup vnode belonging to the file. */
  if ((r = lookup(dirp, resolve, &res, rfp)) != OK) {
        err_code = r;
        unlock_vnode(new_vp);
        return(NULL);
  }

  /* Check whether we already have a vnode for that file */
  if ((vp = find_vnode(res.fs_e, res.inode_nr)) != NULL) {
        unlock_vnode(new_vp);   /* Don't need this anymore */
        do_downgrade = (lock_vnode(vp, initial_locktype) != EBUSY);

        /* Unfortunately, by the time we get the lock, another thread might've
         * rid of the vnode (e.g., find_vnode found the vnode while a
         * req_putnode was being processed). */
        if (vp->v_ref_count == 0) { /* vnode vanished! */
                /* As the lookup before increased the usage counters in the FS,
                 * we can simply set the usage counters to 1 and proceed as
                 * normal, because the putnode resulted in a use count of 1 in
                 * the FS. Other data is still valid, because the vnode was
                 * marked as pending lock, so get_free_vnode hasn't
                 * reinitialized the vnode yet. */
                vp->v_fs_count = 1;
                if (vp->v_mapfs_e != NONE) vp->v_mapfs_count = 1;
        } else {
                vp->v_fs_count++;       /* We got a reference from the FS */
        }

  } else {
        /* Vnode not found, fill in the free vnode's fields */

        new_vp->v_fs_e = res.fs_e;
        new_vp->v_inode_nr = res.inode_nr;
        new_vp->v_mode = res.fmode;
        new_vp->v_size = res.fsize;
        new_vp->v_uid = res.uid;
        new_vp->v_gid = res.gid;
        new_vp->v_sdev = res.dev;

        if( (vmp = find_vmnt(new_vp->v_fs_e)) == NULL)
                  panic("advance: vmnt not found");

        new_vp->v_vmnt = vmp;
        new_vp->v_dev = vmp->m_dev;
        new_vp->v_fs_count = 1;

        vp = new_vp;
  }

  dup_vnode(vp);
  if (do_downgrade) {
        /* Only downgrade a lock if we managed to lock it in the first place */
        *(resolve->l_vnode) = vp;

        if (initial_locktype != resolve->l_vnode_lock)
                tll_downgrade(&vp->v_lock);

#if LOCK_DEBUG
        if (resolve->l_vnode_lock == VNODE_READ)
                fp->fp_vp_rdlocks++;
#endif
  }

  return(vp);
}

/*===========================================================================*
 *                              eat_path                                     *
 *===========================================================================*/
struct vnode *eat_path(resolve, rfp)
struct lookup *resolve;
struct fproc *rfp;
{
/* Resolve path to a vnode. advance does the actual work. */
  struct vnode *start_dir;

  start_dir = (resolve->l_path[0] == '/' ? rfp->fp_rd : rfp->fp_wd);
  return advance(start_dir, resolve, rfp);
}

/*===========================================================================*
 *                              last_dir                                     *
 *===========================================================================*/
struct vnode *last_dir(resolve, rfp)
struct lookup *resolve;
struct fproc *rfp;
{
/* Parse a path, as far as the last directory, fetch the vnode
 * for the last directory into the vnode table, and return a pointer to the
 * vnode. In addition, return the final component of the path in 'string'. If
 * the last directory can't be opened, return NULL and the reason for
 * failure in 'err_code'. We can't parse component by component as that would
 * be too expensive. Alternatively, we cut off the last component of the path,
 * and parse the path up to the penultimate component.
 */

  size_t len;
  char *cp;
  char dir_entry[NAME_MAX+1];
  struct vnode *start_dir, *res_vp, *sym_vp, *loop_start;
  struct vmnt *sym_vmp = NULL;
  int r, symloop = 0, ret_on_symlink = 0;
  struct lookup symlink;

  *resolve->l_vnode = NULL;
  *resolve->l_vmp = NULL;
  loop_start = NULL;
  sym_vp = NULL;

  ret_on_symlink = !!(resolve->l_flags & PATH_RET_SYMLINK);

  do {
        /* Is the path absolute or relative? Initialize 'start_dir'
         * accordingly. Use loop_start in case we're looping.
         */
        if (loop_start != NULL)
                start_dir = loop_start;
        else
                start_dir = (resolve->l_path[0] == '/' ? rfp->fp_rd:rfp->fp_wd);

        len = strlen(resolve->l_path);

        /* If path is empty, return ENOENT. */
        if (len == 0)   {
                err_code = ENOENT;
                res_vp = NULL;
                break;
        }

#if !DO_POSIX_PATHNAME_RES
        /* Remove trailing slashes */
        while (len > 1 && resolve->l_path[len-1] == '/') {
                len--;
                resolve->l_path[len]= '\0';
        }
#endif

        cp = strrchr(resolve->l_path, '/');
        if (cp == NULL) {
                /* Just an entry in the current working directory. Prepend
                 * "./" in front of the path and resolve it.
                 */
                if (strlcpy(dir_entry, resolve->l_path, NAME_MAX+1) >= NAME_MAX + 1) {
                        err_code = ENAMETOOLONG;
                        res_vp = NULL;
                        break;
                }
                dir_entry[NAME_MAX] = '\0';
                resolve->l_path[0] = '.';
                resolve->l_path[1] = '\0';
        } else if (cp[1] == '\0') {
                /* Path ends in a slash. The directory entry is '.' */
                strlcpy(dir_entry, ".", NAME_MAX+1);
        } else {
                /* A path name for the directory and a directory entry */
                if (strlcpy(dir_entry, cp+1, NAME_MAX+1) >= NAME_MAX + 1) {
                        err_code = ENAMETOOLONG;
                        res_vp = NULL;
                        break;
                }
                cp[1] = '\0';
                dir_entry[NAME_MAX] = '\0';
        }

        /* Remove trailing slashes */
        while (cp > resolve->l_path && cp[0] == '/') {
                cp[0]= '\0';
                cp--;
        }

        /* Resolve up to and including the last directory of the path. Turn off
         * PATH_RET_SYMLINK, because we do want to follow the symlink in this
         * case. That is, the flag is meant for the actual filename of the path,
         * not the last directory.
         */
        resolve->l_flags &= ~PATH_RET_SYMLINK;
        if ((res_vp = advance(start_dir, resolve, rfp)) == NULL) {
                break;
        }

        /* If the directory entry is not a symlink we're done now. If it is a
         * symlink, then we're not at the last directory, yet. */

        /* Copy the directory entry back to user_fullpath */
        strlcpy(resolve->l_path, dir_entry, NAME_MAX + 1);

        /* Look up the directory entry, but do not follow the symlink when it
         * is one.
         */
        lookup_init(&symlink, resolve->l_path,
                    resolve->l_flags|PATH_RET_SYMLINK, &sym_vmp, &sym_vp);
        symlink.l_vnode_lock = VNODE_READ;
        symlink.l_vmnt_lock = VMNT_READ;
        sym_vp = advance(res_vp, &symlink, rfp);

        if (sym_vp != NULL && S_ISLNK(sym_vp->v_mode)) {
                /* Last component is a symlink, but if we've been asked to not
                 * resolve it, return now.
                 */
                if (ret_on_symlink) {
                        break;
                }

                r = req_rdlink(sym_vp->v_fs_e, sym_vp->v_inode_nr, NONE,
                                (vir_bytes) resolve->l_path, PATH_MAX - 1, 1);

                if (r < 0) {
                        /* Failed to read link */
                        err_code = r;
                        unlock_vnode(res_vp);
                        unlock_vmnt(*resolve->l_vmp);
                        put_vnode(res_vp);
                        *resolve->l_vmp = NULL;
                        *resolve->l_vnode = NULL;
                        res_vp = NULL;
                        break;
                }
                resolve->l_path[r] = '\0';

                if (strrchr(resolve->l_path, '/') != NULL) {
                        unlock_vnode(sym_vp);
                        unlock_vmnt(*resolve->l_vmp);
                        if (sym_vmp != NULL)
                                unlock_vmnt(sym_vmp);
                        *resolve->l_vmp = NULL;
                        put_vnode(sym_vp);
                        sym_vp = NULL;

                        symloop++;

                        /* Relative symlinks are relative to res_vp, not cwd */
                        if (resolve->l_path[0] != '/') {
                                loop_start = res_vp;
                        } else {
                                /* Absolute symlink, forget about res_vp */
                                unlock_vnode(res_vp);
                                put_vnode(res_vp);
                        }

                        continue;
                }
        }
        break;
  } while (symloop < SYMLOOP_MAX);

  if (symloop >= SYMLOOP_MAX) {
        err_code = ELOOP;
        res_vp = NULL;
  }

  if (sym_vp != NULL) {
        unlock_vnode(sym_vp);
        if (sym_vmp != NULL) {
                unlock_vmnt(sym_vmp);
        }
        put_vnode(sym_vp);
  }

  if (loop_start != NULL) {
        unlock_vnode(loop_start);
        put_vnode(loop_start);
  }

  /* Copy the directory entry back to user_fullpath */
  strlcpy(resolve->l_path, dir_entry, NAME_MAX + 1);

  /* Turn PATH_RET_SYMLINK flag back on if it was on */
  if (ret_on_symlink) resolve->l_flags |= PATH_RET_SYMLINK;

  return(res_vp);
}

/*===========================================================================*
 *                              lookup                                       *
 *===========================================================================*/
static int lookup(start_node, resolve, result_node, rfp)
struct vnode *start_node;
struct lookup *resolve;
node_details_t *result_node;
struct fproc *rfp;
{
/* Resolve a path name relative to start_node. */

  int r, symloop;
  endpoint_t fs_e;
  size_t path_off, path_left_len;
  ino_t dir_ino, root_ino;
  uid_t uid;
  gid_t gid;
  struct vnode *dir_vp;
  struct vmnt *vmp, *vmpres;
  struct lookup_res res;

  assert(resolve->l_vmp);
  assert(resolve->l_vnode);

  *(resolve->l_vmp) = vmpres = NULL; /* No vmnt found nor locked yet */

  /* Empty (start) path? */
  if (resolve->l_path[0] == '\0') {
        result_node->inode_nr = 0;
        return(ENOENT);
  }

  if (!rfp->fp_rd || !rfp->fp_wd) {
        printf("VFS: lookup %d: no rd/wd\n", rfp->fp_endpoint);
        return(ENOENT);
  }

  fs_e = start_node->v_fs_e;
  dir_ino = start_node->v_inode_nr;
  vmpres = find_vmnt(fs_e);

  if (vmpres == NULL) return(EIO);      /* mountpoint vanished? */

  /* Is the process' root directory on the same partition?,
   * if so, set the chroot directory too. */
  if (rfp->fp_rd->v_dev == rfp->fp_wd->v_dev)
        root_ino = rfp->fp_rd->v_inode_nr;
  else
        root_ino = 0;

  /* Set user and group ids according to the system call */
  uid = (job_call_nr == ACCESS ? rfp->fp_realuid : rfp->fp_effuid);
  gid = (job_call_nr == ACCESS ? rfp->fp_realgid : rfp->fp_effgid);

  symloop = 0;  /* Number of symlinks seen so far */

  /* Lock vmnt */
  if ((r = lock_vmnt(vmpres, resolve->l_vmnt_lock)) != OK) {
        if (r == EBUSY) /* vmnt already locked */
                vmpres = NULL;
        else
                return(r);
  }
  *(resolve->l_vmp) = vmpres;

  /* Issue the request */
  r = req_lookup(fs_e, dir_ino, root_ino, uid, gid, resolve, &res, rfp);

  if (r != OK && r != EENTERMOUNT && r != ELEAVEMOUNT && r != ESYMLINK) {
        if (vmpres) unlock_vmnt(vmpres);
        *(resolve->l_vmp) = NULL;
        return(r); /* i.e., an error occured */
  }

  /* While the response is related to mount control set the
   * new requests respectively */
  while (r == EENTERMOUNT || r == ELEAVEMOUNT || r == ESYMLINK) {
        /* Update user_fullpath to reflect what's left to be parsed. */
        path_off = res.char_processed;
        path_left_len = strlen(&resolve->l_path[path_off]);
        memmove(resolve->l_path, &resolve->l_path[path_off], path_left_len);
        resolve->l_path[path_left_len] = '\0'; /* terminate string */

        /* Update the current value of the symloop counter */
        symloop += res.symloop;
        if (symloop > SYMLOOP_MAX) {
                if (vmpres) unlock_vmnt(vmpres);
                *(resolve->l_vmp) = NULL;
                return(ELOOP);
        }

        /* Symlink encountered with absolute path */
        if (r == ESYMLINK) {
                dir_vp = rfp->fp_rd;
                vmp = NULL;
        } else if (r == EENTERMOUNT) {
                /* Entering a new partition */
                dir_vp = NULL;
                /* Start node is now the mounted partition's root node */
                for (vmp = &vmnt[0]; vmp != &vmnt[NR_MNTS]; ++vmp) {
                        if (vmp->m_dev != NO_DEV && vmp->m_mounted_on) {
                           if (vmp->m_mounted_on->v_inode_nr == res.inode_nr &&
                               vmp->m_mounted_on->v_fs_e == res.fs_e) {
                                dir_vp = vmp->m_root_node;
                                break;
                           }
                        }
                }
                if (dir_vp == NULL) {
                        printf("VFS: path lookup error; root node not found\n");
                        if (vmpres) unlock_vmnt(vmpres);
                        *(resolve->l_vmp) = NULL;
                        return(EIO);
                }
        } else {
                /* Climbing up mount */
                /* Find the vmnt that represents the partition on
                 * which we "climb up". */
                if ((vmp = find_vmnt(res.fs_e)) == NULL) {
                        panic("VFS lookup: can't find parent vmnt");
                }

                /* Make sure that the child FS does not feed a bogus path
                 * to the parent FS. That is, when we climb up the tree, we
                 * must've encountered ".." in the path, and that is exactly
                 * what we're going to feed to the parent */
                if(strncmp(resolve->l_path, "..", 2) != 0 ||
                   (resolve->l_path[2] != '\0' && resolve->l_path[2] != '/')) {
                        printf("VFS: bogus path: %s\n", resolve->l_path);
                        if (vmpres) unlock_vmnt(vmpres);
                        *(resolve->l_vmp) = NULL;
                        return(ENOENT);
                }

                /* Start node is the vnode on which the partition is
                 * mounted */
                dir_vp = vmp->m_mounted_on;
        }

        /* Set the starting directories inode number and FS endpoint */
        fs_e = dir_vp->v_fs_e;
        dir_ino = dir_vp->v_inode_nr;

        /* Is the process' root directory on the same partition?,
         * if so, set the chroot directory too. */
        if (dir_vp->v_dev == rfp->fp_rd->v_dev)
                root_ino = rfp->fp_rd->v_inode_nr;
        else
                root_ino = 0;

        /* Unlock a previously locked vmnt if locked and lock new vmnt */
        if (vmpres) unlock_vmnt(vmpres);
        vmpres = find_vmnt(fs_e);
        if (vmpres == NULL) return(EIO);        /* mount point vanished? */
        if ((r = lock_vmnt(vmpres, resolve->l_vmnt_lock)) != OK) {
                if (r == EBUSY)
                        vmpres = NULL;  /* Already locked */
                else
                        return(r);
        }
        *(resolve->l_vmp) = vmpres;

        r = req_lookup(fs_e, dir_ino, root_ino, uid, gid, resolve, &res, rfp);

        if (r != OK && r != EENTERMOUNT && r != ELEAVEMOUNT && r != ESYMLINK) {
                if (vmpres) unlock_vmnt(vmpres);
                *(resolve->l_vmp) = NULL;
                return(r);
        }
  }

  /* Fill in response fields */
  result_node->inode_nr = res.inode_nr;
  result_node->fmode = res.fmode;
  result_node->fsize = res.fsize;
  result_node->dev = res.dev;
  result_node->fs_e = res.fs_e;
  result_node->uid = res.uid;
  result_node->gid = res.gid;

  return(r);
}

/*===========================================================================*
 *                              lookup_init                                  *
 *===========================================================================*/
void lookup_init(resolve, path, flags, vmp, vp)
struct lookup *resolve;
char *path;
int flags;
struct vmnt **vmp;
struct vnode **vp;
{
  assert(vmp != NULL);
  assert(vp != NULL);

  resolve->l_path = path;
  resolve->l_flags = flags;
  resolve->l_vmp = vmp;
  resolve->l_vnode = vp;
  resolve->l_vmnt_lock = TLL_NONE;
  resolve->l_vnode_lock = TLL_NONE;
  *vmp = NULL;  /* Initialize lookup result to NULL */
  *vp = NULL;
}

/*===========================================================================*
 *                              get_name                                     *
 *===========================================================================*/
int get_name(dirp, entry, ename)
struct vnode *dirp;
struct vnode *entry;
char ename[NAME_MAX + 1];
{
#define DIR_ENTRIES 8
#define DIR_ENTRY_SIZE (sizeof(struct dirent) + NAME_MAX)
  u64_t pos, new_pos;
  int r, consumed, totalbytes, name_len;
  char buf[DIR_ENTRY_SIZE * DIR_ENTRIES];
  struct dirent *cur;

  pos = make64(0, 0);

  if (!S_ISDIR(dirp->v_mode)) return(EBADF);

  do {
        r = req_getdents(dirp->v_fs_e, dirp->v_inode_nr, pos, buf, sizeof(buf),
                         &new_pos, 1);

        if (r == 0) {
                return(ENOENT); /* end of entries -- matching inode !found */
        } else if (r < 0) {
                return(r); /* error */
        }

        consumed = 0; /* bytes consumed */
        totalbytes = r; /* number of bytes to consume */

        do {
                cur = (struct dirent *) (buf + consumed);
                name_len = cur->d_reclen - offsetof(struct dirent, d_name) - 1;

                if(cur->d_name + name_len+1 >= &buf[DIR_ENTRIES*DIR_ENTRY_SIZE])
                        return(EINVAL); /* Rubbish in dir entry */
                if (entry->v_inode_nr == cur->d_ino) {
                        /* found the entry we were looking for */
                        int copylen = MIN(name_len + 1, NAME_MAX + 1);
                        if (strlcpy(ename, cur->d_name, copylen) >= copylen) {
                                return(ENAMETOOLONG);
                        }
                        ename[NAME_MAX] = '\0';
                        return(OK);
                }

                /* not a match -- move on to the next dirent */
                consumed += cur->d_reclen;
        } while (consumed < totalbytes);

        pos = new_pos;
  } while (1);
}

/*===========================================================================*
 *                              canonical_path                               *
 *===========================================================================*/
int canonical_path(orig_path, rfp)
char orig_path[PATH_MAX];
struct fproc *rfp;
{
/* Find canonical path of a given path */
  int len = 0;
  int r, symloop = 0;
  struct vnode *dir_vp, *parent_dir;
  struct vmnt *dir_vmp, *parent_vmp;
  char component[NAME_MAX+1];   /* NAME_MAX does /not/ include '\0' */
  char temp_path[PATH_MAX];
  struct lookup resolve;

  dir_vp = NULL;
  strlcpy(temp_path, orig_path, PATH_MAX);
  temp_path[PATH_MAX - 1] = '\0';

  /* First resolve path to the last directory holding the file */
  do {
        if (dir_vp) {
                unlock_vnode(dir_vp);
                unlock_vmnt(dir_vmp);
                put_vnode(dir_vp);
        }

        lookup_init(&resolve, temp_path, PATH_NOFLAGS, &dir_vmp, &dir_vp);
        resolve.l_vmnt_lock = VMNT_READ;
        resolve.l_vnode_lock = VNODE_READ;
        if ((dir_vp = last_dir(&resolve, rfp)) == NULL) return(err_code);

        /* dir_vp points to dir and resolve path now contains only the
         * filename.
         */
        strlcpy(orig_path, temp_path, NAME_MAX+1);      /* Store file name */

        /* check if the file is a symlink, if so resolve it */
        r = rdlink_direct(orig_path, temp_path, rfp);

        if (r <= 0)
                break;

        /* encountered a symlink -- loop again */
        strlcpy(orig_path, temp_path, PATH_MAX);
        symloop++;
  } while (symloop < SYMLOOP_MAX);

  if (symloop >= SYMLOOP_MAX) {
        if (dir_vp) {
                unlock_vnode(dir_vp);
                unlock_vmnt(dir_vmp);
                put_vnode(dir_vp);
        }
        return(ELOOP);
  }

  /* We've got the filename and the actual directory holding the file. From
   * here we start building up the canonical path by climbing up the tree */
  while (dir_vp != rfp->fp_rd) {

        strlcpy(temp_path, "..", NAME_MAX+1);

        /* check if we're at the root node of the file system */
        if (dir_vp->v_vmnt->m_root_node == dir_vp) {
                unlock_vnode(dir_vp);
                unlock_vmnt(dir_vmp);
                put_vnode(dir_vp);
                dir_vp = dir_vp->v_vmnt->m_mounted_on;
                dir_vmp = dir_vp->v_vmnt;
                if (lock_vmnt(dir_vmp, VMNT_READ) != OK)
                        panic("failed to lock vmnt");
                if (lock_vnode(dir_vp, VNODE_READ) != OK)
                        panic("failed to lock vnode");
                dup_vnode(dir_vp);
        }

        lookup_init(&resolve, temp_path, PATH_NOFLAGS, &parent_vmp,
                    &parent_dir);
        resolve.l_vmnt_lock = VMNT_READ;
        resolve.l_vnode_lock = VNODE_READ;

        if ((parent_dir = advance(dir_vp, &resolve, rfp)) == NULL) {
                unlock_vnode(dir_vp);
                unlock_vmnt(dir_vmp);
                put_vnode(dir_vp);
                return(err_code);
        }

        /* now we have to retrieve the name of the parent directory */
        if (get_name(parent_dir, dir_vp, component) != OK) {
                unlock_vnode(parent_dir);
                unlock_vmnt(parent_vmp);
                unlock_vnode(dir_vp);
                unlock_vmnt(dir_vmp);
                put_vnode(parent_dir);
                put_vnode(dir_vp);
                return(ENOENT);
        }

        len += strlen(component) + 1;
        if (len >= PATH_MAX) {
                /* adding the component to orig_path would exceed PATH_MAX */
                unlock_vnode(parent_dir);
                unlock_vmnt(parent_vmp);
                unlock_vnode(dir_vp);
                unlock_vmnt(dir_vmp);
                put_vnode(parent_dir);
                put_vnode(dir_vp);
                return(ENOMEM);
        }

        /* Store result of component in orig_path. First make space by moving
         * the contents of orig_path to the right. Move strlen + 1 bytes to
         * include the terminating '\0'. Move to strlen + 1 bytes to reserve
         * space for the slash.
         */
        memmove(orig_path+strlen(component)+1, orig_path, strlen(orig_path)+1);
        /* Copy component into canon_path */
        memmove(orig_path, component, strlen(component));
        /* Put slash into place */
        orig_path[strlen(component)] = '/';

        /* Store parent_dir result, and continue the loop once more */
        unlock_vnode(dir_vp);
        unlock_vmnt(dir_vmp);
        put_vnode(dir_vp);
        dir_vp = parent_dir;
  }

  unlock_vnode(dir_vp);
  unlock_vmnt(parent_vmp);

  put_vnode(dir_vp);

  /* add the leading slash */
  if (strlen(orig_path) >= PATH_MAX) return(ENAMETOOLONG);
  memmove(orig_path+1, orig_path, strlen(orig_path));
  orig_path[0] = '/';

  return(OK);
}

/*===========================================================================*
 *                              check_perms                                  *
 *===========================================================================*/
static int check_perms(ep, io_gr, pathlen)
endpoint_t ep;
cp_grant_id_t io_gr;
size_t pathlen;
{
  int r, slot;
  struct vnode *vp;
  struct vmnt *vmp;
  struct fproc *rfp;
  char canon_path[PATH_MAX];
  struct lookup resolve;

  if (isokendpt(ep, &slot) != OK) return(EINVAL);
  if (pathlen < UNIX_PATH_MAX || pathlen >= PATH_MAX) return(EINVAL);

  rfp = &(fproc[slot]);
  r = sys_safecopyfrom(PFS_PROC_NR, io_gr, (vir_bytes) 0,
                                (vir_bytes) canon_path, pathlen);
  if (r != OK) return(r);
  canon_path[pathlen] = '\0';

  /* Turn path into canonical path to the socket file */
  if ((r = canonical_path(canon_path, rfp)) != OK) return(r);
  if (strlen(canon_path) >= pathlen) return(ENAMETOOLONG);

  /* copy canon_path back to PFS */
  r = sys_safecopyto(PFS_PROC_NR, (cp_grant_id_t) io_gr, (vir_bytes) 0,
                                (vir_bytes) canon_path, pathlen);
  if (r != OK) return(r);

  /* Now do permissions checking */
  lookup_init(&resolve, canon_path, PATH_NOFLAGS, &vmp, &vp);
  resolve.l_vmnt_lock = VMNT_READ;
  resolve.l_vnode_lock = VNODE_READ;
  if ((vp = eat_path(&resolve, rfp)) == NULL) return(err_code);

  /* check permissions */
  r = forbidden(rfp, vp, (R_BIT | W_BIT));

  unlock_vnode(vp);
  unlock_vmnt(vmp);

  put_vnode(vp);
  return(r);
}

/*===========================================================================*
 *                              do_check_perms                               *
 *===========================================================================*/
int do_check_perms(void)
{
  return check_perms(job_m_in.USER_ENDPT, (cp_grant_id_t) job_m_in.IO_GRANT,
                     (size_t) job_m_in.COUNT);
}