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: %pd (%p) uid %d any %d\n",
  69                  dentry, 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                 spin_lock(&dentry->d_lock);
  76                 hlist_for_each_entry(fid, h, dlist) {
  77                         if (any || uid_eq(fid->uid, uid)) {
  78                                 ret = fid;
  79                                 break;
  80                         }
  81                 }
  82                 spin_unlock(&dentry->d_lock);
  83         }
  84
  85         return ret;
  86 }
  87
  88 /*
  89  * We need to hold v9ses->rename_sem as long as we hold references
  90  * to returned path array. Array element contain pointers to
  91  * dentry names.
  92  */
  93 static int build_path_from_dentry(struct v9fs_session_info *v9ses,
  94                                   struct dentry *dentry, const unsigned char ***names)
  95 {
  96         int n = 0, i;
  97         const unsigned char **wnames;
  98         struct dentry *ds;
  99
 100         for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
 101                 n++;
 102
 103         wnames = kmalloc_array(n, sizeof(char *), GFP_KERNEL);
 104         if (!wnames)
 105                 goto err_out;
 106
 107         for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
 108                 wnames[i] = ds->d_name.name;
 109
 110         *names = wnames;
 111         return n;
 112 err_out:
 113         return -ENOMEM;
 114 }
 115
 116 static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
 117                                                kuid_t uid, int any)
 118 {
 119         struct dentry *ds;
 120         const unsigned char **wnames, *uname;
 121         int i, n, l, clone, access;
 122         struct v9fs_session_info *v9ses;
 123         struct p9_fid *fid, *old_fid = NULL;
 124
 125         v9ses = v9fs_dentry2v9ses(dentry);
 126         access = v9ses->flags & V9FS_ACCESS_MASK;
 127         fid = v9fs_fid_find(dentry, uid, any);
 128         if (fid)
 129                 return fid;
 130         /*
 131          * we don't have a matching fid. To do a TWALK we need
 132          * parent fid. We need to prevent rename when we want to
 133          * look at the parent.
 134          */
 135         down_read(&v9ses->rename_sem);
 136         ds = dentry->d_parent;
 137         fid = v9fs_fid_find(ds, uid, any);
 138         if (fid) {
 139                 /* Found the parent fid do a lookup with that */
 140                 fid = p9_client_walk(fid, 1, &dentry->d_name.name, 1);
 141                 goto fid_out;
 142         }
 143         up_read(&v9ses->rename_sem);
 144
 145         /* start from the root and try to do a lookup */
 146         fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
 147         if (!fid) {
 148                 /* the user is not attached to the fs yet */
 149                 if (access == V9FS_ACCESS_SINGLE)
 150                         return ERR_PTR(-EPERM);
 151
 152                 if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
 153                                 uname = NULL;
 154                 else
 155                         uname = v9ses->uname;
 156
 157                 fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
 158                                        v9ses->aname);
 159                 if (IS_ERR(fid))
 160                         return fid;
 161
 162                 v9fs_fid_add(dentry->d_sb->s_root, fid);
 163         }
 164         /* If we are root ourself just return that */
 165         if (dentry->d_sb->s_root == dentry)
 166                 return fid;
 167         /*
 168          * Do a multipath walk with attached root.
 169          * When walking parent we need to make sure we
 170          * don't have a parallel rename happening
 171          */
 172         down_read(&v9ses->rename_sem);
 173         n  = build_path_from_dentry(v9ses, dentry, &wnames);
 174         if (n < 0) {
 175                 fid = ERR_PTR(n);
 176                 goto err_out;
 177         }
 178         clone = 1;
 179         i = 0;
 180         while (i < n) {
 181                 l = min(n - i, P9_MAXWELEM);
 182                 /*
 183                  * We need to hold rename lock when doing a multipath
 184                  * walk to ensure none of the patch component change
 185                  */
 186                 fid = p9_client_walk(fid, l, &wnames[i], clone);
 187                 if (IS_ERR(fid)) {
 188                         if (old_fid) {
 189                                 /*
 190                                  * If we fail, clunk fid which are mapping
 191                                  * to path component and not the last component
 192                                  * of the path.
 193                                  */
 194                                 p9_client_clunk(old_fid);
 195                         }
 196                         kfree(wnames);
 197                         goto err_out;
 198                 }
 199                 old_fid = fid;
 200                 i += l;
 201                 clone = 0;
 202         }
 203         kfree(wnames);
 204 fid_out:
 205         if (!IS_ERR(fid)) {
 206                 spin_lock(&dentry->d_lock);
 207                 if (d_unhashed(dentry)) {
 208                         spin_unlock(&dentry->d_lock);
 209                         p9_client_clunk(fid);
 210                         fid = ERR_PTR(-ENOENT);
 211                 } else {
 212                         __add_fid(dentry, fid);
 213                         spin_unlock(&dentry->d_lock);
 214                 }
 215         }
 216 err_out:
 217         up_read(&v9ses->rename_sem);
 218         return fid;
 219 }
 220
 221 /**
 222  * v9fs_fid_lookup - lookup for a fid, try to walk if not found
 223  * @dentry: dentry to look for fid in
 224  *
 225  * Look for a fid in the specified dentry for the current user.
 226  * If no fid is found, try to create one walking from a fid from the parent
 227  * dentry (if it has one), or the root dentry. If the user haven't accessed
 228  * the fs yet, attach now and walk from the root.
 229  */
 230
 231 struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
 232 {
 233         kuid_t uid;
 234         int  any, access;
 235         struct v9fs_session_info *v9ses;
 236
 237         v9ses = v9fs_dentry2v9ses(dentry);
 238         access = v9ses->flags & V9FS_ACCESS_MASK;
 239         switch (access) {
 240         case V9FS_ACCESS_SINGLE:
 241         case V9FS_ACCESS_USER:
 242         case V9FS_ACCESS_CLIENT:
 243                 uid = current_fsuid();
 244                 any = 0;
 245                 break;
 246
 247         case V9FS_ACCESS_ANY:
 248                 uid = v9ses->uid;
 249                 any = 1;
 250                 break;
 251
 252         default:
 253                 uid = INVALID_UID;
 254                 any = 0;
 255                 break;
 256         }
 257         return v9fs_fid_lookup_with_uid(dentry, uid, any);
 258 }
 259
 260 struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
 261 {
 262         int err;
 263         struct p9_fid *fid;
 264
 265         fid = clone_fid(v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0));
 266         if (IS_ERR(fid))
 267                 goto error_out;
 268         /*
 269          * writeback fid will only be used to write back the
 270          * dirty pages. We always request for the open fid in read-write
 271          * mode so that a partial page write which result in page
 272          * read can work.
 273          */
 274         err = p9_client_open(fid, O_RDWR);
 275         if (err < 0) {
 276                 p9_client_clunk(fid);
 277                 fid = ERR_PTR(err);
 278                 goto error_out;
 279         }
 280 error_out:
 281         return fid;
 282 }