New locking/refcounting for fs_struct
[linux-2.6.git] / fs / fs_struct.c
1 #include <linux/module.h>
2 #include <linux/sched.h>
3 #include <linux/fs.h>
4 #include <linux/path.h>
5 #include <linux/slab.h>
6
7 /*
8  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
9  * It can block.
10  */
11 void set_fs_root(struct fs_struct *fs, struct path *path)
12 {
13         struct path old_root;
14
15         write_lock(&fs->lock);
16         old_root = fs->root;
17         fs->root = *path;
18         path_get(path);
19         write_unlock(&fs->lock);
20         if (old_root.dentry)
21                 path_put(&old_root);
22 }
23
24 /*
25  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
26  * It can block.
27  */
28 void set_fs_pwd(struct fs_struct *fs, struct path *path)
29 {
30         struct path old_pwd;
31
32         write_lock(&fs->lock);
33         old_pwd = fs->pwd;
34         fs->pwd = *path;
35         path_get(path);
36         write_unlock(&fs->lock);
37
38         if (old_pwd.dentry)
39                 path_put(&old_pwd);
40 }
41
42 void chroot_fs_refs(struct path *old_root, struct path *new_root)
43 {
44         struct task_struct *g, *p;
45         struct fs_struct *fs;
46         int count = 0;
47
48         read_lock(&tasklist_lock);
49         do_each_thread(g, p) {
50                 task_lock(p);
51                 fs = p->fs;
52                 if (fs) {
53                         write_lock(&fs->lock);
54                         if (fs->root.dentry == old_root->dentry
55                             && fs->root.mnt == old_root->mnt) {
56                                 path_get(new_root);
57                                 fs->root = *new_root;
58                                 count++;
59                         }
60                         if (fs->pwd.dentry == old_root->dentry
61                             && fs->pwd.mnt == old_root->mnt) {
62                                 path_get(new_root);
63                                 fs->pwd = *new_root;
64                                 count++;
65                         }
66                         write_unlock(&fs->lock);
67                 }
68                 task_unlock(p);
69         } while_each_thread(g, p);
70         read_unlock(&tasklist_lock);
71         while (count--)
72                 path_put(old_root);
73 }
74
75 void free_fs_struct(struct fs_struct *fs)
76 {
77         path_put(&fs->root);
78         path_put(&fs->pwd);
79         kmem_cache_free(fs_cachep, fs);
80 }
81
82 void exit_fs(struct task_struct *tsk)
83 {
84         struct fs_struct *fs = tsk->fs;
85
86         if (fs) {
87                 int kill;
88                 task_lock(tsk);
89                 write_lock(&fs->lock);
90                 tsk->fs = NULL;
91                 kill = !--fs->users;
92                 write_unlock(&fs->lock);
93                 task_unlock(tsk);
94                 if (kill)
95                         free_fs_struct(fs);
96         }
97 }
98
99 struct fs_struct *copy_fs_struct(struct fs_struct *old)
100 {
101         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
102         /* We don't need to lock fs - think why ;-) */
103         if (fs) {
104                 fs->users = 1;
105                 fs->in_exec = 0;
106                 rwlock_init(&fs->lock);
107                 fs->umask = old->umask;
108                 read_lock(&old->lock);
109                 fs->root = old->root;
110                 path_get(&old->root);
111                 fs->pwd = old->pwd;
112                 path_get(&old->pwd);
113                 read_unlock(&old->lock);
114         }
115         return fs;
116 }
117
118 int unshare_fs_struct(void)
119 {
120         struct fs_struct *fs = current->fs;
121         struct fs_struct *new_fs = copy_fs_struct(fs);
122         int kill;
123
124         if (!new_fs)
125                 return -ENOMEM;
126
127         task_lock(current);
128         write_lock(&fs->lock);
129         kill = !--fs->users;
130         current->fs = new_fs;
131         write_unlock(&fs->lock);
132         task_unlock(current);
133
134         if (kill)
135                 free_fs_struct(fs);
136
137         return 0;
138 }
139 EXPORT_SYMBOL_GPL(unshare_fs_struct);
140
141 /* to be mentioned only in INIT_TASK */
142 struct fs_struct init_fs = {
143         .users          = 1,
144         .lock           = __RW_LOCK_UNLOCKED(init_fs.lock),
145         .umask          = 0022,
146 };
147
148 void daemonize_fs_struct(void)
149 {
150         struct fs_struct *fs = current->fs;
151
152         if (fs) {
153                 int kill;
154
155                 task_lock(current);
156
157                 write_lock(&init_fs.lock);
158                 init_fs.users++;
159                 write_unlock(&init_fs.lock);
160
161                 write_lock(&fs->lock);
162                 current->fs = &init_fs;
163                 kill = !--fs->users;
164                 write_unlock(&fs->lock);
165
166                 task_unlock(current);
167                 if (kill)
168                         free_fs_struct(fs);
169         }
170 }