ia64/linux-2.6.18-xen.hg

view fs/filesystems.c @ 524:7f8b544237bf

netfront: Allow netfront in domain 0.

This is useful if your physical network device is in a utility domain.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Apr 15 15:18:58 2008 +0100 (2008-04-15)
parents 831230e53067
children
line source
1 /*
2 * linux/fs/filesystems.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 *
6 * table of configured filesystems
7 */
9 #include <linux/syscalls.h>
10 #include <linux/fs.h>
11 #include <linux/slab.h>
12 #include <linux/kmod.h>
13 #include <linux/init.h>
14 #include <linux/module.h>
15 #include <linux/sched.h> /* for 'current' */
16 #include <asm/uaccess.h>
18 /*
19 * Handling of filesystem drivers list.
20 * Rules:
21 * Inclusion to/removals from/scanning of list are protected by spinlock.
22 * During the unload module must call unregister_filesystem().
23 * We can access the fields of list element if:
24 * 1) spinlock is held or
25 * 2) we hold the reference to the module.
26 * The latter can be guaranteed by call of try_module_get(); if it
27 * returned 0 we must skip the element, otherwise we got the reference.
28 * Once the reference is obtained we can drop the spinlock.
29 */
31 static struct file_system_type *file_systems;
32 static DEFINE_RWLOCK(file_systems_lock);
34 /* WARNING: This can be used only if we _already_ own a reference */
35 void get_filesystem(struct file_system_type *fs)
36 {
37 __module_get(fs->owner);
38 }
40 void put_filesystem(struct file_system_type *fs)
41 {
42 module_put(fs->owner);
43 }
45 static struct file_system_type **find_filesystem(const char *name)
46 {
47 struct file_system_type **p;
48 for (p=&file_systems; *p; p=&(*p)->next)
49 if (strcmp((*p)->name,name) == 0)
50 break;
51 return p;
52 }
54 /**
55 * register_filesystem - register a new filesystem
56 * @fs: the file system structure
57 *
58 * Adds the file system passed to the list of file systems the kernel
59 * is aware of for mount and other syscalls. Returns 0 on success,
60 * or a negative errno code on an error.
61 *
62 * The &struct file_system_type that is passed is linked into the kernel
63 * structures and must not be freed until the file system has been
64 * unregistered.
65 */
67 int register_filesystem(struct file_system_type * fs)
68 {
69 int res = 0;
70 struct file_system_type ** p;
72 if (!fs)
73 return -EINVAL;
74 if (fs->next)
75 return -EBUSY;
76 INIT_LIST_HEAD(&fs->fs_supers);
77 write_lock(&file_systems_lock);
78 p = find_filesystem(fs->name);
79 if (*p)
80 res = -EBUSY;
81 else
82 *p = fs;
83 write_unlock(&file_systems_lock);
84 return res;
85 }
87 EXPORT_SYMBOL(register_filesystem);
89 /**
90 * unregister_filesystem - unregister a file system
91 * @fs: filesystem to unregister
92 *
93 * Remove a file system that was previously successfully registered
94 * with the kernel. An error is returned if the file system is not found.
95 * Zero is returned on a success.
96 *
97 * Once this function has returned the &struct file_system_type structure
98 * may be freed or reused.
99 */
101 int unregister_filesystem(struct file_system_type * fs)
102 {
103 struct file_system_type ** tmp;
105 write_lock(&file_systems_lock);
106 tmp = &file_systems;
107 while (*tmp) {
108 if (fs == *tmp) {
109 *tmp = fs->next;
110 fs->next = NULL;
111 write_unlock(&file_systems_lock);
112 return 0;
113 }
114 tmp = &(*tmp)->next;
115 }
116 write_unlock(&file_systems_lock);
117 return -EINVAL;
118 }
120 EXPORT_SYMBOL(unregister_filesystem);
122 static int fs_index(const char __user * __name)
123 {
124 struct file_system_type * tmp;
125 char * name;
126 int err, index;
128 name = getname(__name);
129 err = PTR_ERR(name);
130 if (IS_ERR(name))
131 return err;
133 err = -EINVAL;
134 read_lock(&file_systems_lock);
135 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
136 if (strcmp(tmp->name,name) == 0) {
137 err = index;
138 break;
139 }
140 }
141 read_unlock(&file_systems_lock);
142 putname(name);
143 return err;
144 }
146 static int fs_name(unsigned int index, char __user * buf)
147 {
148 struct file_system_type * tmp;
149 int len, res;
151 read_lock(&file_systems_lock);
152 for (tmp = file_systems; tmp; tmp = tmp->next, index--)
153 if (index <= 0 && try_module_get(tmp->owner))
154 break;
155 read_unlock(&file_systems_lock);
156 if (!tmp)
157 return -EINVAL;
159 /* OK, we got the reference, so we can safely block */
160 len = strlen(tmp->name) + 1;
161 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
162 put_filesystem(tmp);
163 return res;
164 }
166 static int fs_maxindex(void)
167 {
168 struct file_system_type * tmp;
169 int index;
171 read_lock(&file_systems_lock);
172 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
173 ;
174 read_unlock(&file_systems_lock);
175 return index;
176 }
178 /*
179 * Whee.. Weird sysv syscall.
180 */
181 asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
182 {
183 int retval = -EINVAL;
185 switch (option) {
186 case 1:
187 retval = fs_index((const char __user *) arg1);
188 break;
190 case 2:
191 retval = fs_name(arg1, (char __user *) arg2);
192 break;
194 case 3:
195 retval = fs_maxindex();
196 break;
197 }
198 return retval;
199 }
201 int get_filesystem_list(char * buf)
202 {
203 int len = 0;
204 struct file_system_type * tmp;
206 read_lock(&file_systems_lock);
207 tmp = file_systems;
208 while (tmp && len < PAGE_SIZE - 80) {
209 len += sprintf(buf+len, "%s\t%s\n",
210 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
211 tmp->name);
212 tmp = tmp->next;
213 }
214 read_unlock(&file_systems_lock);
215 return len;
216 }
218 struct file_system_type *get_fs_type(const char *name)
219 {
220 struct file_system_type *fs;
222 read_lock(&file_systems_lock);
223 fs = *(find_filesystem(name));
224 if (fs && !try_module_get(fs->owner))
225 fs = NULL;
226 read_unlock(&file_systems_lock);
227 if (!fs && (request_module("%s", name) == 0)) {
228 read_lock(&file_systems_lock);
229 fs = *(find_filesystem(name));
230 if (fs && !try_module_get(fs->owner))
231 fs = NULL;
232 read_unlock(&file_systems_lock);
233 }
234 return fs;
235 }
237 EXPORT_SYMBOL(get_fs_type);