This can be used to share devices/named pipes/sockets between
                hosts.  This functionality will be expanded in later versions.
 
+  access       there are three access modes.
+                       user  = if a user tries to access a file on v9fs
+                               filesystem for the first time, v9fs sends an
+                               attach command (Tattach) for that user.
+                               This is the default mode.
+                       <uid> = allows only user with uid=<uid> to access
+                               the files on the mounted filesystem
+                       any   = v9fs does single attach and performs all
+                               operations as one user
+
 RESOURCES
 =========
 
 
 /*
  * V9FS FID Management
  *
+ *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
  *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
  *
  *  This program is free software; you can redistribute it and/or modify
 #include "fid.h"
 
 /**
- * v9fs_fid_insert - add a fid to a dentry
+ * v9fs_fid_add - add a fid to a dentry
+ * @dentry: dentry that the fid is being added to
  * @fid: fid to add
- * @dentry: dentry that it is being added to
  *
  */
 
 }
 
 /**
- * v9fs_fid_lookup - return a locked fid from a dentry
+ * v9fs_fid_find - retrieve a fid that belongs to the specified uid
  * @dentry: dentry to look for fid in
- *
- * find a fid in the dentry, obtain its semaphore and return a reference to it.
- * code calling lookup is responsible for releasing lock
- *
- * TODO: only match fids that have the same uid as current user
+ * @uid: return fid that belongs to the specified user
+ * @any: if non-zero, return any fid associated with the dentry
  *
  */
 
-struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
+static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
 {
        struct v9fs_dentry *dent;
-       struct p9_fid *fid;
-
-       P9_DPRINTK(P9_DEBUG_VFS, " dentry: %s (%p)\n", dentry->d_iname, dentry);
-       dent = dentry->d_fsdata;
-       if (dent)
-               fid = list_entry(dent->fidlist.next, struct p9_fid, dlist);
-       else
-               fid = ERR_PTR(-EBADF);
+       struct p9_fid *fid, *ret;
+
+       P9_DPRINTK(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d\n",
+               dentry->d_iname, dentry, uid, any);
+       dent = (struct v9fs_dentry *) dentry->d_fsdata;
+       ret = NULL;
+       if (dent) {
+               spin_lock(&dent->lock);
+               list_for_each_entry(fid, &dent->fidlist, dlist) {
+                       if (any || fid->uid == uid) {
+                               ret = fid;
+                               break;
+                       }
+               }
+               spin_unlock(&dent->lock);
+       }
 
-       P9_DPRINTK(P9_DEBUG_VFS, " fid: %p\n", fid);
-       return fid;
+       return ret;
 }
 
 /**
- * v9fs_fid_clone - lookup the fid for a dentry, clone a private copy and
- *     release it
+ * v9fs_fid_lookup - lookup for a fid, try to walk if not found
  * @dentry: dentry to look for fid in
  *
- * find a fid in the dentry and then clone to a new private fid
- *
- * TODO: only match fids that have the same uid as current user
- *
+ * Look for a fid in the specified dentry for the current user.
+ * If no fid is found, try to create one walking from a fid from the parent
+ * dentry (if it has one), or the root dentry. If the user haven't accessed
+ * the fs yet, attach now and walk from the root.
  */
 
-struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
+struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
 {
-       struct p9_fid *ofid, *fid;
+       int i, n, l, clone, any, access;
+       u32 uid;
+       struct p9_fid *fid;
+       struct dentry *d, *ds;
+       struct v9fs_session_info *v9ses;
+       char **wnames, *uname;
+
+       v9ses = v9fs_inode2v9ses(dentry->d_inode);
+       access = v9ses->flags & V9FS_ACCESS_MASK;
+       switch (access) {
+       case V9FS_ACCESS_SINGLE:
+       case V9FS_ACCESS_USER:
+               uid = current->fsuid;
+               any = 0;
+               break;
+
+       case V9FS_ACCESS_ANY:
+               uid = v9ses->uid;
+               any = 1;
+               break;
+
+       default:
+               uid = ~0;
+               any = 0;
+               break;
+       }
 
-       P9_DPRINTK(P9_DEBUG_VFS, " dentry: %s (%p)\n", dentry->d_iname, dentry);
-       ofid = v9fs_fid_lookup(dentry);
-       if (IS_ERR(ofid))
-               return ofid;
+       fid = v9fs_fid_find(dentry, uid, any);
+       if (fid)
+               return fid;
+
+       ds = dentry->d_parent;
+       fid = v9fs_fid_find(ds, uid, any);
+       if (!fid) { /* walk from the root */
+               n = 0;
+               for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
+                       n++;
+
+               fid = v9fs_fid_find(ds, uid, any);
+               if (!fid) { /* the user is not attached to the fs yet */
+                       if (access == V9FS_ACCESS_SINGLE)
+                               return ERR_PTR(-EPERM);
+
+                       if (v9fs_extended(v9ses))
+                               uname = NULL;
+                       else
+                               uname = v9ses->uname;
+
+                       fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
+                               v9ses->aname);
+
+                       if (IS_ERR(fid))
+                               return fid;
+
+                       v9fs_fid_add(ds, fid);
+               }
+       } else /* walk from the parent */
+               n = 1;
+
+       if (ds == dentry)
+               return fid;
+
+       wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
+       if (!wnames)
+               return ERR_PTR(-ENOMEM);
+
+       for (d = dentry, i = n; i >= 0; i--, d = d->d_parent)
+               wnames[i] = (char *) d->d_name.name;
+
+       clone = 1;
+       i = 0;
+       while (i < n) {
+               l = min(n - i, P9_MAXWELEM);
+               fid = p9_client_walk(fid, l, &wnames[i], clone);
+               if (!fid) {
+                       kfree(wnames);
+                       return fid;
+               }
+
+               i += l;
+               clone = 0;
+       }
 
-       fid = p9_client_walk(ofid, 0, NULL, 1);
+       kfree(wnames);
+       v9fs_fid_add(dentry, fid);
        return fid;
 }
+
+struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
+{
+       struct p9_fid *fid, *ret;
+
+       fid = v9fs_fid_lookup(dentry);
+       if (IS_ERR(fid))
+               return fid;
+
+       ret = p9_client_walk(fid, 0, NULL, 1);
+       return ret;
+}
 
        Opt_legacy, Opt_nodevmap,
        /* Cache options */
        Opt_cache_loose,
+       /* Access options */
+       Opt_access,
        /* Error token */
        Opt_err
 };
        {Opt_nodevmap, "nodevmap"},
        {Opt_cache_loose, "cache=loose"},
        {Opt_cache_loose, "loose"},
+       {Opt_access, "access=%s"},
        {Opt_err, NULL}
 };
 
        char *p;
        int option;
        int ret;
+       char *s, *e;
 
        /* setup defaults */
        v9ses->maxdata = 8192;
-       v9ses->flags = V9FS_EXTENDED;
        v9ses->afid = ~0;
        v9ses->debug = 0;
        v9ses->cache = 0;
                        v9ses->trans = v9fs_match_trans(&args[0]);
                        break;
                case Opt_uname:
-                       match_strcpy(v9ses->name, &args[0]);
+                       match_strcpy(v9ses->uname, &args[0]);
                        break;
                case Opt_remotename:
-                       match_strcpy(v9ses->remotename, &args[0]);
+                       match_strcpy(v9ses->aname, &args[0]);
                        break;
                case Opt_legacy:
                        v9ses->flags &= ~V9FS_EXTENDED;
                case Opt_cache_loose:
                        v9ses->cache = CACHE_LOOSE;
                        break;
+
+               case Opt_access:
+                       s = match_strdup(&args[0]);
+                       v9ses->flags &= ~V9FS_ACCESS_MASK;
+                       if (strcmp(s, "user") == 0)
+                               v9ses->flags |= V9FS_ACCESS_USER;
+                       else if (strcmp(s, "any") == 0)
+                               v9ses->flags |= V9FS_ACCESS_ANY;
+                       else {
+                               v9ses->flags |= V9FS_ACCESS_SINGLE;
+                               v9ses->uid = simple_strtol(s, &e, 10);
+                               if (*e != '\0')
+                                       v9ses->uid = ~0;
+                       }
+                       break;
+
                default:
                        continue;
                }
        struct p9_trans *trans = NULL;
        struct p9_fid *fid;
 
-       v9ses->name = __getname();
-       if (!v9ses->name)
+       v9ses->uname = __getname();
+       if (!v9ses->uname)
                return ERR_PTR(-ENOMEM);
 
-       v9ses->remotename = __getname();
-       if (!v9ses->remotename) {
-               __putname(v9ses->name);
+       v9ses->aname = __getname();
+       if (!v9ses->aname) {
+               __putname(v9ses->uname);
                return ERR_PTR(-ENOMEM);
        }
 
-       strcpy(v9ses->name, V9FS_DEFUSER);
-       strcpy(v9ses->remotename, V9FS_DEFANAME);
+       v9ses->flags = V9FS_EXTENDED | V9FS_ACCESS_USER;
+       strcpy(v9ses->uname, V9FS_DEFUSER);
+       strcpy(v9ses->aname, V9FS_DEFANAME);
+       v9ses->uid = ~0;
        v9ses->dfltuid = V9FS_DEFUID;
        v9ses->dfltgid = V9FS_DEFGID;
-
        v9ses->options = kstrdup(data, GFP_KERNEL);
        v9fs_parse_options(v9ses);
 
                goto error;
        }
 
-       fid = p9_client_attach(v9ses->clnt, NULL, v9ses->name,
-                                                       v9ses->remotename);
+       if (!v9ses->clnt->dotu)
+               v9ses->flags &= ~V9FS_EXTENDED;
+
+       /* for legacy mode, fall back to V9FS_ACCESS_ANY */
+       if (!v9fs_extended(v9ses) &&
+               ((v9ses->flags&V9FS_ACCESS_MASK) == V9FS_ACCESS_USER)) {
+
+               v9ses->flags &= ~V9FS_ACCESS_MASK;
+               v9ses->flags |= V9FS_ACCESS_ANY;
+               v9ses->uid = ~0;
+       }
+
+       fid = p9_client_attach(v9ses->clnt, NULL, v9ses->uname, ~0,
+                                                       v9ses->aname);
        if (IS_ERR(fid)) {
                retval = PTR_ERR(fid);
                fid = NULL;
                goto error;
        }
 
+       if ((v9ses->flags & V9FS_ACCESS_MASK) == V9FS_ACCESS_SINGLE)
+               fid->uid = v9ses->uid;
+       else
+               fid->uid = ~0;
+
        return fid;
 
 error:
                v9ses->clnt = NULL;
        }
 
-       __putname(v9ses->name);
-       __putname(v9ses->remotename);
+       __putname(v9ses->uname);
+       __putname(v9ses->aname);
        kfree(v9ses->options);
 }
 
 
        unsigned int cache;     /* cache mode */
 
        char *options;          /* copy of mount options */
-       char *name;             /* user name to mount as */
-       char *remotename;       /* name of remote hierarchy being mounted */
+       char *uname;            /* user name to mount as */
+       char *aname;            /* name of remote hierarchy being mounted */
        unsigned int dfltuid;   /* default uid/muid for legacy support */
        unsigned int dfltgid;   /* default gid for legacy support */
+       u32 uid;                /* if ACCESS_SINGLE, the uid that has access */
        struct p9_trans_module *trans; /* 9p transport */
        struct p9_client *clnt; /* 9p client */
        struct dentry *debugfs_dir;
 
 /* session flags */
 enum {
-       V9FS_EXTENDED,
+       V9FS_EXTENDED           = 0x01, /* 9P2000.u */
+       V9FS_ACCESS_MASK        = 0x06, /* access mask */
+       V9FS_ACCESS_SINGLE      = 0x02, /* only one user can access the files */
+       V9FS_ACCESS_USER        = 0x04, /* attache per user */
+       V9FS_ACCESS_ANY         = 0x06, /* use the same attach for all users */
 };
 
 /* possible values of ->cache */
 
        file_inode = file->d_inode;
        v9ses = v9fs_inode2v9ses(file_inode);
        v9fid = v9fs_fid_clone(file);
-       if(IS_ERR(v9fid))
+       if (IS_ERR(v9fid))
                return PTR_ERR(v9fid);
 
        return p9_client_remove(v9fid);
        fid = NULL;
        name = (char *) dentry->d_name.name;
        dfid = v9fs_fid_clone(dentry->d_parent);
-       if(IS_ERR(dfid)) {
+       if (IS_ERR(dfid)) {
                err = PTR_ERR(dfid);
                dfid = NULL;
                goto error;
                goto error;
        }
 
-       if(v9ses->cache)
+       if (v9ses->cache)
                dentry->d_op = &v9fs_cached_dentry_operations;
        else
                dentry->d_op = &v9fs_dentry_operations;
        if (result < 0)
                goto error;
 
-       if((fid->qid.version)&&(v9ses->cache))
+       if ((fid->qid.version) && (v9ses->cache))
                dentry->d_op = &v9fs_cached_dentry_operations;
        else
                dentry->d_op = &v9fs_dentry_operations;
        old_inode = old_dentry->d_inode;
        v9ses = v9fs_inode2v9ses(old_inode);
        oldfid = v9fs_fid_lookup(old_dentry);
-       if(IS_ERR(oldfid))
+       if (IS_ERR(oldfid))
                return PTR_ERR(oldfid);
 
        olddirfid = v9fs_fid_clone(old_dentry->d_parent);
-       if(IS_ERR(olddirfid)) {
+       if (IS_ERR(olddirfid)) {
                retval = PTR_ERR(olddirfid);
                goto done;
        }
 
        newdirfid = v9fs_fid_clone(new_dentry->d_parent);
-       if(IS_ERR(newdirfid)) {
+       if (IS_ERR(newdirfid)) {
                retval = PTR_ERR(newdirfid);
                goto clunk_olddir;
        }
        }
 
        v9fs_blank_wstat(&wstat);
-       wstat.muid = v9ses->name;
+       wstat.muid = v9ses->uname;
        wstat.name = (char *) new_dentry->d_name.name;
        retval = p9_client_wstat(oldfid, &wstat);
 
        retval = -EPERM;
        v9ses = v9fs_inode2v9ses(dentry->d_inode);
        fid = v9fs_fid_lookup(dentry);
-       if(IS_ERR(fid))
+       if (IS_ERR(fid))
                return PTR_ERR(fid);
 
        if (!v9fs_extended(v9ses))
                old_dentry->d_name.name);
 
        oldfid = v9fs_fid_clone(old_dentry);
-       if(IS_ERR(oldfid))
+       if (IS_ERR(oldfid))
                return PTR_ERR(oldfid);
 
        name = __getname();
 
        u32 afid;
        struct p9_str uname;
        struct p9_str aname;
+       u32 n_uname;            /* 9P2000.u extensions */
 };
 
 struct p9_rauth {
        u32 afid;
        struct p9_str uname;
        struct p9_str aname;
+       u32 n_uname;            /* 9P2000.u extensions */
 };
 
 struct p9_rattach {
 void p9_set_tag(struct p9_fcall *fc, u16 tag);
 struct p9_fcall *p9_create_tversion(u32 msize, char *version);
 struct p9_fcall *p9_create_tattach(u32 fid, u32 afid, char *uname,
-       char *aname);
-struct p9_fcall *p9_create_tauth(u32 afid, char *uname, char *aname);
+       char *aname, u32 n_uname, int dotu);
+struct p9_fcall *p9_create_tauth(u32 afid, char *uname, char *aname,
+       u32 n_uname, int dotu);
 struct p9_fcall *p9_create_tflush(u16 oldtag);
 struct p9_fcall *p9_create_twalk(u32 fid, u32 newfid, u16 nwname,
        char **wnames);
 
 void p9_client_destroy(struct p9_client *clnt);
 void p9_client_disconnect(struct p9_client *clnt);
 struct p9_fid *p9_client_attach(struct p9_client *clnt, struct p9_fid *afid,
-                                                    char *uname, char *aname);
-struct p9_fid *p9_client_auth(struct p9_client *clnt, char *uname, char *aname);
+                                       char *uname, u32 n_uname, char *aname);
+struct p9_fid *p9_client_auth(struct p9_client *clnt, char *uname,
+                                               u32 n_uname, char *aname);
 struct p9_fid *p9_client_walk(struct p9_fid *oldfid, int nwname, char **wnames,
                                                                int clone);
 int p9_client_open(struct p9_fid *fid, int mode);
 
 EXPORT_SYMBOL(p9_client_disconnect);
 
 struct p9_fid *p9_client_attach(struct p9_client *clnt, struct p9_fid *afid,
-       char *uname, char *aname)
+       char *uname, u32 n_uname, char *aname)
 {
        int err;
        struct p9_fcall *tc, *rc;
                goto error;
        }
 
-       tc = p9_create_tattach(fid->fid, afid?afid->fid:P9_NOFID, uname, aname);
+       tc = p9_create_tattach(fid->fid, afid?afid->fid:P9_NOFID, uname, aname,
+               n_uname, clnt->dotu);
        if (IS_ERR(tc)) {
                err = PTR_ERR(tc);
                tc = NULL;
 }
 EXPORT_SYMBOL(p9_client_attach);
 
-struct p9_fid *p9_client_auth(struct p9_client *clnt, char *uname, char *aname)
+struct p9_fid *p9_client_auth(struct p9_client *clnt, char *uname,
+       u32 n_uname, char *aname)
 {
        int err;
        struct p9_fcall *tc, *rc;
                goto error;
        }
 
-       tc = p9_create_tauth(fid->fid, uname, aname);
+       tc = p9_create_tauth(fid->fid, uname, aname, n_uname, clnt->dotu);
        if (IS_ERR(tc)) {
                err = PTR_ERR(tc);
                tc = NULL;
 
 }
 EXPORT_SYMBOL(p9_create_tversion);
 
-struct p9_fcall *p9_create_tauth(u32 afid, char *uname, char *aname)
+struct p9_fcall *p9_create_tauth(u32 afid, char *uname, char *aname,
+       u32 n_uname, int dotu)
 {
        int size;
        struct p9_fcall *fc;
        struct cbuf *bufp = &buffer;
 
        /* afid[4] uname[s] aname[s] */
-       size = 4 + 2 + strlen(uname) + 2 + strlen(aname);
+       size = 4 + 2 + 2;
+       if (uname)
+               size += strlen(uname);
+
+       if (aname)
+               size += strlen(aname);
+
+       if (dotu)
+               size += 4;      /* n_uname */
+
        fc = p9_create_common(bufp, size, P9_TAUTH);
        if (IS_ERR(fc))
                goto error;
        p9_put_int32(bufp, afid, &fc->params.tauth.afid);
        p9_put_str(bufp, uname, &fc->params.tauth.uname);
        p9_put_str(bufp, aname, &fc->params.tauth.aname);
+       if (dotu)
+               p9_put_int32(bufp, n_uname, &fc->params.tauth.n_uname);
 
        if (buf_check_overflow(bufp)) {
                kfree(fc);
 EXPORT_SYMBOL(p9_create_tauth);
 
 struct p9_fcall *
-p9_create_tattach(u32 fid, u32 afid, char *uname, char *aname)
+p9_create_tattach(u32 fid, u32 afid, char *uname, char *aname,
+       u32 n_uname, int dotu)
 {
        int size;
        struct p9_fcall *fc;
        struct cbuf *bufp = &buffer;
 
        /* fid[4] afid[4] uname[s] aname[s] */
-       size = 4 + 4 + 2 + strlen(uname) + 2 + strlen(aname);
+       size = 4 + 4 + 2 + 2;
+       if (uname)
+               size += strlen(uname);
+
+       if (aname)
+               size += strlen(aname);
+
+       if (dotu)
+               size += 4;      /* n_uname */
+
        fc = p9_create_common(bufp, size, P9_TATTACH);
        if (IS_ERR(fc))
                goto error;
        p9_put_int32(bufp, afid, &fc->params.tattach.afid);
        p9_put_str(bufp, uname, &fc->params.tattach.uname);
        p9_put_str(bufp, aname, &fc->params.tattach.aname);
+       if (dotu)
+               p9_put_int32(bufp, n_uname, &fc->params.tattach.n_uname);
 
 error:
        return fc;