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Linux/fs/9p/fid.c

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  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                 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, char ***names)
 95 {
 96         int n = 0, i;
 97         char **wnames;
 98         struct dentry *ds;
 99 
100         for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
101                 n++;
102 
103         wnames = kmalloc(sizeof(char *) * n, 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] = (char  *)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         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, (char **)&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_fid_clone(struct dentry *dentry)
261 {
262         struct p9_fid *fid, *ret;
263 
264         fid = v9fs_fid_lookup(dentry);
265         if (IS_ERR(fid))
266                 return fid;
267 
268         ret = p9_client_walk(fid, 0, NULL, 1);
269         return ret;
270 }
271 
272 static struct p9_fid *v9fs_fid_clone_with_uid(struct dentry *dentry, kuid_t uid)
273 {
274         struct p9_fid *fid, *ret;
275 
276         fid = v9fs_fid_lookup_with_uid(dentry, uid, 0);
277         if (IS_ERR(fid))
278                 return fid;
279 
280         ret = p9_client_walk(fid, 0, NULL, 1);
281         return ret;
282 }
283 
284 struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
285 {
286         int err;
287         struct p9_fid *fid;
288 
289         fid = v9fs_fid_clone_with_uid(dentry, GLOBAL_ROOT_UID);
290         if (IS_ERR(fid))
291                 goto error_out;
292         /*
293          * writeback fid will only be used to write back the
294          * dirty pages. We always request for the open fid in read-write
295          * mode so that a partial page write which result in page
296          * read can work.
297          */
298         err = p9_client_open(fid, O_RDWR);
299         if (err < 0) {
300                 p9_client_clunk(fid);
301                 fid = ERR_PTR(err);
302                 goto error_out;
303         }
304 error_out:
305         return fid;
306 }
307 

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