xref: /openbmc/linux/fs/9p/fid.c (revision 495311927ffbe3604e915aeafdf03325e9925b9d)
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 int v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
45 {
46 	struct v9fs_dentry *dent;
47 
48 	P9_DPRINTK(P9_DEBUG_VFS, "fid %d dentry %s\n",
49 					fid->fid, dentry->d_name.name);
50 
51 	dent = dentry->d_fsdata;
52 	if (!dent) {
53 		dent = kmalloc(sizeof(struct v9fs_dentry), GFP_KERNEL);
54 		if (!dent)
55 			return -ENOMEM;
56 
57 		spin_lock_init(&dent->lock);
58 		INIT_LIST_HEAD(&dent->fidlist);
59 		dentry->d_fsdata = dent;
60 	}
61 
62 	spin_lock(&dent->lock);
63 	list_add(&fid->dlist, &dent->fidlist);
64 	spin_unlock(&dent->lock);
65 
66 	return 0;
67 }
68 
69 /**
70  * v9fs_fid_find - retrieve a fid that belongs to the specified uid
71  * @dentry: dentry to look for fid in
72  * @uid: return fid that belongs to the specified user
73  * @any: if non-zero, return any fid associated with the dentry
74  *
75  */
76 
77 static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)
78 {
79 	struct v9fs_dentry *dent;
80 	struct p9_fid *fid, *ret;
81 
82 	P9_DPRINTK(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d\n",
83 		dentry->d_name.name, dentry, uid, any);
84 	dent = (struct v9fs_dentry *) dentry->d_fsdata;
85 	ret = NULL;
86 	if (dent) {
87 		spin_lock(&dent->lock);
88 		list_for_each_entry(fid, &dent->fidlist, dlist) {
89 			if (any || fid->uid == uid) {
90 				ret = fid;
91 				break;
92 			}
93 		}
94 		spin_unlock(&dent->lock);
95 	}
96 
97 	return ret;
98 }
99 
100 /*
101  * We need to hold v9ses->rename_sem as long as we hold references
102  * to returned path array. Array element contain pointers to
103  * dentry names.
104  */
105 static int build_path_from_dentry(struct v9fs_session_info *v9ses,
106 				  struct dentry *dentry, char ***names)
107 {
108 	int n = 0, i;
109 	char **wnames;
110 	struct dentry *ds;
111 
112 	for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
113 		n++;
114 
115 	wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
116 	if (!wnames)
117 		goto err_out;
118 
119 	for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
120 		wnames[i] = (char  *)ds->d_name.name;
121 
122 	*names = wnames;
123 	return n;
124 err_out:
125 	return -ENOMEM;
126 }
127 
128 /**
129  * v9fs_fid_lookup - lookup for a fid, try to walk if not found
130  * @dentry: dentry to look for fid in
131  *
132  * Look for a fid in the specified dentry for the current user.
133  * If no fid is found, try to create one walking from a fid from the parent
134  * dentry (if it has one), or the root dentry. If the user haven't accessed
135  * the fs yet, attach now and walk from the root.
136  */
137 
138 struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
139 {
140 	int i, n, l, clone, any, access;
141 	u32 uid;
142 	struct p9_fid *fid, *old_fid = NULL;
143 	struct dentry *ds;
144 	struct v9fs_session_info *v9ses;
145 	char **wnames, *uname;
146 
147 	v9ses = v9fs_inode2v9ses(dentry->d_inode);
148 	access = v9ses->flags & V9FS_ACCESS_MASK;
149 	switch (access) {
150 	case V9FS_ACCESS_SINGLE:
151 	case V9FS_ACCESS_USER:
152 		uid = current_fsuid();
153 		any = 0;
154 		break;
155 
156 	case V9FS_ACCESS_ANY:
157 		uid = v9ses->uid;
158 		any = 1;
159 		break;
160 
161 	default:
162 		uid = ~0;
163 		any = 0;
164 		break;
165 	}
166 
167 	fid = v9fs_fid_find(dentry, uid, any);
168 	if (fid)
169 		return fid;
170 	/*
171 	 * we don't have a matching fid. To do a TWALK we need
172 	 * parent fid. We need to prevent rename when we want to
173 	 * look at the parent.
174 	 */
175 	down_read(&v9ses->rename_sem);
176 	ds = dentry->d_parent;
177 	fid = v9fs_fid_find(ds, uid, any);
178 	if (fid) {
179 		/* Found the parent fid do a lookup with that */
180 		fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
181 		goto fid_out;
182 	}
183 	up_read(&v9ses->rename_sem);
184 
185 	/* start from the root and try to do a lookup */
186 	fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
187 	if (!fid) {
188 		/* the user is not attached to the fs yet */
189 		if (access == V9FS_ACCESS_SINGLE)
190 			return ERR_PTR(-EPERM);
191 
192 		if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
193 				uname = NULL;
194 		else
195 			uname = v9ses->uname;
196 
197 		fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
198 				       v9ses->aname);
199 		if (IS_ERR(fid))
200 			return fid;
201 
202 		v9fs_fid_add(dentry->d_sb->s_root, fid);
203 	}
204 	/* If we are root ourself just return that */
205 	if (dentry->d_sb->s_root == dentry)
206 		return fid;
207 	/*
208 	 * Do a multipath walk with attached root.
209 	 * When walking parent we need to make sure we
210 	 * don't have a parallel rename happening
211 	 */
212 	down_read(&v9ses->rename_sem);
213 	n  = build_path_from_dentry(v9ses, dentry, &wnames);
214 	if (n < 0) {
215 		fid = ERR_PTR(n);
216 		goto err_out;
217 	}
218 	clone = 1;
219 	i = 0;
220 	while (i < n) {
221 		l = min(n - i, P9_MAXWELEM);
222 		/*
223 		 * We need to hold rename lock when doing a multipath
224 		 * walk to ensure none of the patch component change
225 		 */
226 		fid = p9_client_walk(fid, l, &wnames[i], clone);
227 		if (IS_ERR(fid)) {
228 			if (old_fid) {
229 				/*
230 				 * If we fail, clunk fid which are mapping
231 				 * to path component and not the last component
232 				 * of the path.
233 				 */
234 				p9_client_clunk(old_fid);
235 			}
236 			kfree(wnames);
237 			goto err_out;
238 		}
239 		old_fid = fid;
240 		i += l;
241 		clone = 0;
242 	}
243 	kfree(wnames);
244 fid_out:
245 	v9fs_fid_add(dentry, fid);
246 err_out:
247 	up_read(&v9ses->rename_sem);
248 	return fid;
249 }
250 
251 struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
252 {
253 	struct p9_fid *fid, *ret;
254 
255 	fid = v9fs_fid_lookup(dentry);
256 	if (IS_ERR(fid))
257 		return fid;
258 
259 	ret = p9_client_walk(fid, 0, NULL, 1);
260 	return ret;
261 }
262