fs/9p/fid.c

   1 /*
   2  * V9FS FID Management
   3  *
   4  *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>
   5  *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>
   6  *
   7  *  This program is free software; you can redistribute it and/or modify
   8  *  it under the terms of the GNU General Public License version 2
   9  *  as published by the Free Software Foundation.
  10  *
  11  *  This program is distributed in the hope that it will be useful,
  12  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  *  GNU General Public License for more details.
  15  *
  16  *  You should have received a copy of the GNU General Public License
  17  *  along with this program; if not, write to:
  18  *  Free Software Foundation
  19  *  51 Franklin Street, Fifth Floor
  20  *  Boston, MA  02111-1301  USA
  21  *
  22  */
  23
  24 #include <linux/module.h>
  25 #include <linux/errno.h>
  26 #include <linux/fs.h>
  27 #include <linux/slab.h>
  28 #include <linux/sched.h>
  29 #include <linux/idr.h>
  30 #include <net/9p/9p.h>
  31 #include <net/9p/client.h>
  32
  33 #include "v9fs.h"
  34 #include "v9fs_vfs.h"
  35 #include "fid.h"
  36
  37 /**
  38  * v9fs_fid_add - add a fid to a dentry
  39  * @dentry: dentry that the fid is being added to
  40  * @fid: fid to add
  41  *
  42  */
  43
  44 static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
  45 {
  46         hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
  47 }
  48
  49 void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
  50 {
  51         spin_lock(&dentry->d_lock);
  52         __add_fid(dentry, fid);
  53         spin_unlock(&dentry->d_lock);
  54 }
  55
  56 /**
  57  * v9fs_fid_find - retrieve a fid that belongs to the specified uid
  58  * @dentry: dentry to look for fid in
  59  * @uid: return fid that belongs to the specified user
  60  * @any: if non-zero, return any fid associated with the dentry
  61  *
  62  */
  63
  64 static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
  65 {
  66         struct p9_fid *fid, *ret;
  67
  68         p9_debug(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d\n",
  69                  dentry->d_name.name, dentry, from_kuid(&init_user_ns, uid),
  70                  any);
  71         ret = NULL;
  72         /* we'll recheck under lock if there's anything to look in */
  73         if (dentry->d_fsdata) {
  74                 struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
  75                 struct hlist_node *n;
  76                 spin_lock(&dentry->d_lock);
  77                 hlist_for_each_entry(fid, n, h, dlist) {
  78                         if (any || uid_eq(fid->uid, uid)) {
  79                                 ret = fid;
  80                                 break;
  81                         }
  82                 }
  83                 spin_unlock(&dentry->d_lock);
  84         }
  85
  86         return ret;
  87 }
  88
  89 /*
  90  * We need to hold v9ses->rename_sem as long as we hold references
  91  * to returned path array. Array element contain pointers to
  92  * dentry names.
  93  */
  94 static int build_path_from_dentry(struct v9fs_session_info *v9ses,
  95                                   struct dentry *dentry, char ***names)
  96 {
  97         int n = 0, i;
  98         char **wnames;
  99         struct dentry *ds;
 100
 101         for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
 102                 n++;
 103
 104         wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
 105         if (!wnames)
 106                 goto err_out;
 107
 108         for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
 109                 wnames[i] = (char  *)ds->d_name.name;
 110
 111         *names = wnames;
 112         return n;
 113 err_out:
 114         return -ENOMEM;
 115 }
 116
 117 static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 118                                                kuid_t uid, int any)
 119 {
 120         struct dentry *ds;
 121         char **wnames, *uname;
 122         int i, n, l, clone, access;
 123         struct v9fs_session_info *v9ses;
 124         struct p9_fid *fid, *old_fid = NULL;
 125
 126         v9ses = v9fs_dentry2v9ses(dentry);
 127         access = v9ses->flags & V9FS_ACCESS_MASK;
 128         fid = v9fs_fid_find(dentry, uid, any);
 129         if (fid)
 130                 return fid;
 131         /*
 132          * we don't have a matching fid. To do a TWALK we need
 133          * parent fid. We need to prevent rename when we want to
 134          * look at the parent.
 135          */
 136         down_read(&v9ses->rename_sem);
 137         ds = dentry->d_parent;
 138         fid = v9fs_fid_find(ds, uid, any);
 139         if (fid) {
 140                 /* Found the parent fid do a lookup with that */
 141                 fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
 142                 goto fid_out;
 143         }
 144         up_read(&v9ses->rename_sem);
 145
 146         /* start from the root and try to do a lookup */
 147         fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
 148         if (!fid) {
 149                 /* the user is not attached to the fs yet */
 150                 if (access == V9FS_ACCESS_SINGLE)
 151                         return ERR_PTR(-EPERM);
 152
 153                 if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
 154                                 uname = NULL;
 155                 else
 156                         uname = v9ses->uname;
 157
 158                 fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
 159                                        v9ses->aname);
 160                 if (IS_ERR(fid))
 161                         return fid;
 162
 163                 v9fs_fid_add(dentry->d_sb->s_root, fid);
 164         }
 165         /* If we are root ourself just return that */
 166         if (dentry->d_sb->s_root == dentry)
 167                 return fid;
 168         /*
 169          * Do a multipath walk with attached root.
 170          * When walking parent we need to make sure we
 171          * don't have a parallel rename happening
 172          */
 173         down_read(&v9ses->rename_sem);
 174         n  = build_path_from_dentry(v9ses, dentry, &wnames);
 175         if (n < 0) {
 176                 fid = ERR_PTR(n);
 177                 goto err_out;
 178         }
 179         clone = 1;
 180         i = 0;
 181         while (i < n) {
 182                 l = min(n - i, P9_MAXWELEM);
 183                 /*
 184                  * We need to hold rename lock when doing a multipath
 185                  * walk to ensure none of the patch component change
 186                  */
 187                 fid = p9_client_walk(fid, l, &wnames[i], clone);
 188                 if (IS_ERR(fid)) {
 189                         if (old_fid) {
 190                                 /*
 191                                  * If we fail, clunk fid which are mapping
 192                                  * to path component and not the last component
 193                                  * of the path.
 194                                  */
 195                                 p9_client_clunk(old_fid);
 196                         }
 197                         kfree(wnames);
 198                         goto err_out;
 199                 }
 200                 old_fid = fid;
 201                 i += l;
 202                 clone = 0;
 203         }
 204         kfree(wnames);
 205 fid_out:
 206         if (!IS_ERR(fid)) {
 207                 spin_lock(&dentry->d_lock);
 208                 if (d_unhashed(dentry)) {
 209                         spin_unlock(&dentry->d_lock);
 210                         p9_client_clunk(fid);
 211                         fid = ERR_PTR(-ENOENT);
 212                 } else {
 213                         __add_fid(dentry, fid);
 214                         spin_unlock(&dentry->d_lock);
 215                 }
 216         }
 217 err_out:
 218         up_read(&v9ses->rename_sem);
 219         return fid;
 220 }
 221
 222 /**
 223  * v9fs_fid_lookup - lookup for a fid, try to walk if not found
 224  * @dentry: dentry to look for fid in
 225  *
 226  * Look for a fid in the specified dentry for the current user.
 227  * If no fid is found, try to create one walking from a fid from the parent
 228  * dentry (if it has one), or the root dentry. If the user haven't accessed
 229  * the fs yet, attach now and walk from the root.
 230  */
 231
 232 struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
 233 {
 234         kuid_t uid;
 235         int  any, access;
 236         struct v9fs_session_info *v9ses;
 237
 238         v9ses = v9fs_dentry2v9ses(dentry);
 239         access = v9ses->flags & V9FS_ACCESS_MASK;
 240         switch (access) {
 241         case V9FS_ACCESS_SINGLE:
 242         case V9FS_ACCESS_USER:
 243         case V9FS_ACCESS_CLIENT:
 244                 uid = current_fsuid();
 245                 any = 0;
 246                 break;
 247
 248         case V9FS_ACCESS_ANY:
 249                 uid = v9ses->uid;
 250                 any = 1;
 251                 break;
 252
 253         default:
 254                 uid = INVALID_UID;
 255                 any = 0;
 256                 break;
 257         }
 258         return v9fs_fid_lookup_with_uid(dentry, uid, any);
 259 }
 260
 261 struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
 262 {
 263         struct p9_fid *fid, *ret;
 264
 265         fid = v9fs_fid_lookup(dentry);
 266         if (IS_ERR(fid))
 267                 return fid;
 268
 269         ret = p9_client_walk(fid, 0, NULL, 1);
 270         return ret;
 271 }
 272
 273 static struct p9_fid *v9fs_fid_clone_with_uid(struct dentry *dentry, kuid_t uid)
 274 {
 275         struct p9_fid *fid, *ret;
 276
 277         fid = v9fs_fid_lookup_with_uid(dentry, uid, 0);
 278         if (IS_ERR(fid))
 279                 return fid;
 280
 281         ret = p9_client_walk(fid, 0, NULL, 1);
 282         return ret;
 283 }
 284
 285 struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
 286 {
 287         int err;
 288         struct p9_fid *fid;
 289
 290         fid = v9fs_fid_clone_with_uid(dentry, GLOBAL_ROOT_UID);
 291         if (IS_ERR(fid))
 292                 goto error_out;
 293         /*
 294          * writeback fid will only be used to write back the
 295          * dirty pages. We always request for the open fid in read-write
 296          * mode so that a partial page write which result in page
 297          * read can work.
 298          */
 299         err = p9_client_open(fid, O_RDWR);
 300         if (err < 0) {
 301                 p9_client_clunk(fid);
 302                 fid = ERR_PTR(err);
 303                 goto error_out;
 304         }
 305 error_out:
 306         return fid;
 307 }