1/*
2 FUSE: Filesystem in Userspace
3 Copyright (C) 2001-2008 Miklos Szeredi <miklos@szeredi.hu>
4
5 This program can be distributed under the terms of the GNU GPL.
6 See the file COPYING.
7*/
8
9#include "fuse_i.h"
10
11#include <linux/init.h>
12#include <linux/module.h>
13#include <linux/fs_context.h>
14
15#define FUSE_CTL_SUPER_MAGIC 0x65735543
16
17/*
18 * This is non-NULL when the single instance of the control filesystem
19 * exists. Protected by fuse_mutex
20 */
21static struct super_block *fuse_control_sb;
22
23static struct fuse_conn *fuse_ctl_file_conn_get(struct file *file)
24{
25 struct fuse_conn *fc;
26 mutex_lock(&fuse_mutex);
27 fc = file_inode(f: file)->i_private;
28 if (fc)
29 fc = fuse_conn_get(fc);
30 mutex_unlock(lock: &fuse_mutex);
31 return fc;
32}
33
34static ssize_t fuse_conn_abort_write(struct file *file, const char __user *buf,
35 size_t count, loff_t *ppos)
36{
37 struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
38 if (fc) {
39 if (fc->abort_err)
40 fc->aborted = true;
41 fuse_abort_conn(fc);
42 fuse_conn_put(fc);
43 }
44 return count;
45}
46
47static ssize_t fuse_conn_waiting_read(struct file *file, char __user *buf,
48 size_t len, loff_t *ppos)
49{
50 char tmp[32];
51 size_t size;
52
53 if (!*ppos) {
54 long value;
55 struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
56 if (!fc)
57 return 0;
58
59 value = atomic_read(v: &fc->num_waiting);
60 file->private_data = (void *)value;
61 fuse_conn_put(fc);
62 }
63 size = sprintf(buf: tmp, fmt: "%ld\n", (long)file->private_data);
64 return simple_read_from_buffer(to: buf, count: len, ppos, from: tmp, available: size);
65}
66
67static ssize_t fuse_conn_limit_read(struct file *file, char __user *buf,
68 size_t len, loff_t *ppos, unsigned val)
69{
70 char tmp[32];
71 size_t size = sprintf(buf: tmp, fmt: "%u\n", val);
72
73 return simple_read_from_buffer(to: buf, count: len, ppos, from: tmp, available: size);
74}
75
76static ssize_t fuse_conn_limit_write(struct file *file, const char __user *buf,
77 size_t count, loff_t *ppos, unsigned *val,
78 unsigned global_limit)
79{
80 unsigned long t;
81 unsigned limit = (1 << 16) - 1;
82 int err;
83
84 if (*ppos)
85 return -EINVAL;
86
87 err = kstrtoul_from_user(s: buf, count, base: 0, res: &t);
88 if (err)
89 return err;
90
91 if (!capable(CAP_SYS_ADMIN))
92 limit = min(limit, global_limit);
93
94 if (t > limit)
95 return -EINVAL;
96
97 *val = t;
98
99 return count;
100}
101
102static ssize_t fuse_conn_max_background_read(struct file *file,
103 char __user *buf, size_t len,
104 loff_t *ppos)
105{
106 struct fuse_conn *fc;
107 unsigned val;
108
109 fc = fuse_ctl_file_conn_get(file);
110 if (!fc)
111 return 0;
112
113 val = READ_ONCE(fc->max_background);
114 fuse_conn_put(fc);
115
116 return fuse_conn_limit_read(file, buf, len, ppos, val);
117}
118
119static ssize_t fuse_conn_max_background_write(struct file *file,
120 const char __user *buf,
121 size_t count, loff_t *ppos)
122{
123 unsigned val;
124 ssize_t ret;
125
126 ret = fuse_conn_limit_write(file, buf, count, ppos, val: &val,
127 global_limit: max_user_bgreq);
128 if (ret > 0) {
129 struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
130 if (fc) {
131 spin_lock(lock: &fc->bg_lock);
132 fc->max_background = val;
133 fc->blocked = fc->num_background >= fc->max_background;
134 if (!fc->blocked)
135 wake_up(&fc->blocked_waitq);
136 spin_unlock(lock: &fc->bg_lock);
137 fuse_conn_put(fc);
138 }
139 }
140
141 return ret;
142}
143
144static ssize_t fuse_conn_congestion_threshold_read(struct file *file,
145 char __user *buf, size_t len,
146 loff_t *ppos)
147{
148 struct fuse_conn *fc;
149 unsigned val;
150
151 fc = fuse_ctl_file_conn_get(file);
152 if (!fc)
153 return 0;
154
155 val = READ_ONCE(fc->congestion_threshold);
156 fuse_conn_put(fc);
157
158 return fuse_conn_limit_read(file, buf, len, ppos, val);
159}
160
161static ssize_t fuse_conn_congestion_threshold_write(struct file *file,
162 const char __user *buf,
163 size_t count, loff_t *ppos)
164{
165 unsigned val;
166 struct fuse_conn *fc;
167 ssize_t ret;
168
169 ret = fuse_conn_limit_write(file, buf, count, ppos, val: &val,
170 global_limit: max_user_congthresh);
171 if (ret <= 0)
172 goto out;
173 fc = fuse_ctl_file_conn_get(file);
174 if (!fc)
175 goto out;
176
177 WRITE_ONCE(fc->congestion_threshold, val);
178 fuse_conn_put(fc);
179out:
180 return ret;
181}
182
183static const struct file_operations fuse_ctl_abort_ops = {
184 .open = nonseekable_open,
185 .write = fuse_conn_abort_write,
186 .llseek = no_llseek,
187};
188
189static const struct file_operations fuse_ctl_waiting_ops = {
190 .open = nonseekable_open,
191 .read = fuse_conn_waiting_read,
192 .llseek = no_llseek,
193};
194
195static const struct file_operations fuse_conn_max_background_ops = {
196 .open = nonseekable_open,
197 .read = fuse_conn_max_background_read,
198 .write = fuse_conn_max_background_write,
199 .llseek = no_llseek,
200};
201
202static const struct file_operations fuse_conn_congestion_threshold_ops = {
203 .open = nonseekable_open,
204 .read = fuse_conn_congestion_threshold_read,
205 .write = fuse_conn_congestion_threshold_write,
206 .llseek = no_llseek,
207};
208
209static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
210 struct fuse_conn *fc,
211 const char *name,
212 int mode, int nlink,
213 const struct inode_operations *iop,
214 const struct file_operations *fop)
215{
216 struct dentry *dentry;
217 struct inode *inode;
218
219 BUG_ON(fc->ctl_ndents >= FUSE_CTL_NUM_DENTRIES);
220 dentry = d_alloc_name(parent, name);
221 if (!dentry)
222 return NULL;
223
224 inode = new_inode(sb: fuse_control_sb);
225 if (!inode) {
226 dput(dentry);
227 return NULL;
228 }
229
230 inode->i_ino = get_next_ino();
231 inode->i_mode = mode;
232 inode->i_uid = fc->user_id;
233 inode->i_gid = fc->group_id;
234 simple_inode_init_ts(inode);
235 /* setting ->i_op to NULL is not allowed */
236 if (iop)
237 inode->i_op = iop;
238 inode->i_fop = fop;
239 set_nlink(inode, nlink);
240 inode->i_private = fc;
241 d_add(dentry, inode);
242
243 fc->ctl_dentry[fc->ctl_ndents++] = dentry;
244
245 return dentry;
246}
247
248/*
249 * Add a connection to the control filesystem (if it exists). Caller
250 * must hold fuse_mutex
251 */
252int fuse_ctl_add_conn(struct fuse_conn *fc)
253{
254 struct dentry *parent;
255 char name[32];
256
257 if (!fuse_control_sb || fc->no_control)
258 return 0;
259
260 parent = fuse_control_sb->s_root;
261 inc_nlink(inode: d_inode(dentry: parent));
262 sprintf(buf: name, fmt: "%u", fc->dev);
263 parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, nlink: 2,
264 iop: &simple_dir_inode_operations,
265 fop: &simple_dir_operations);
266 if (!parent)
267 goto err;
268
269 if (!fuse_ctl_add_dentry(parent, fc, name: "waiting", S_IFREG | 0400, nlink: 1,
270 NULL, fop: &fuse_ctl_waiting_ops) ||
271 !fuse_ctl_add_dentry(parent, fc, name: "abort", S_IFREG | 0200, nlink: 1,
272 NULL, fop: &fuse_ctl_abort_ops) ||
273 !fuse_ctl_add_dentry(parent, fc, name: "max_background", S_IFREG | 0600,
274 nlink: 1, NULL, fop: &fuse_conn_max_background_ops) ||
275 !fuse_ctl_add_dentry(parent, fc, name: "congestion_threshold",
276 S_IFREG | 0600, nlink: 1, NULL,
277 fop: &fuse_conn_congestion_threshold_ops))
278 goto err;
279
280 return 0;
281
282 err:
283 fuse_ctl_remove_conn(fc);
284 return -ENOMEM;
285}
286
287/*
288 * Remove a connection from the control filesystem (if it exists).
289 * Caller must hold fuse_mutex
290 */
291void fuse_ctl_remove_conn(struct fuse_conn *fc)
292{
293 int i;
294
295 if (!fuse_control_sb || fc->no_control)
296 return;
297
298 for (i = fc->ctl_ndents - 1; i >= 0; i--) {
299 struct dentry *dentry = fc->ctl_dentry[i];
300 d_inode(dentry)->i_private = NULL;
301 if (!i) {
302 /* Get rid of submounts: */
303 d_invalidate(dentry);
304 }
305 dput(dentry);
306 }
307 drop_nlink(inode: d_inode(dentry: fuse_control_sb->s_root));
308}
309
310static int fuse_ctl_fill_super(struct super_block *sb, struct fs_context *fsc)
311{
312 static const struct tree_descr empty_descr = {""};
313 struct fuse_conn *fc;
314 int err;
315
316 err = simple_fill_super(sb, FUSE_CTL_SUPER_MAGIC, &empty_descr);
317 if (err)
318 return err;
319
320 mutex_lock(&fuse_mutex);
321 BUG_ON(fuse_control_sb);
322 fuse_control_sb = sb;
323 list_for_each_entry(fc, &fuse_conn_list, entry) {
324 err = fuse_ctl_add_conn(fc);
325 if (err) {
326 fuse_control_sb = NULL;
327 mutex_unlock(lock: &fuse_mutex);
328 return err;
329 }
330 }
331 mutex_unlock(lock: &fuse_mutex);
332
333 return 0;
334}
335
336static int fuse_ctl_get_tree(struct fs_context *fsc)
337{
338 return get_tree_single(fc: fsc, fill_super: fuse_ctl_fill_super);
339}
340
341static const struct fs_context_operations fuse_ctl_context_ops = {
342 .get_tree = fuse_ctl_get_tree,
343};
344
345static int fuse_ctl_init_fs_context(struct fs_context *fsc)
346{
347 fsc->ops = &fuse_ctl_context_ops;
348 return 0;
349}
350
351static void fuse_ctl_kill_sb(struct super_block *sb)
352{
353 struct fuse_conn *fc;
354
355 mutex_lock(&fuse_mutex);
356 fuse_control_sb = NULL;
357 list_for_each_entry(fc, &fuse_conn_list, entry)
358 fc->ctl_ndents = 0;
359 mutex_unlock(lock: &fuse_mutex);
360
361 kill_litter_super(sb);
362}
363
364static struct file_system_type fuse_ctl_fs_type = {
365 .owner = THIS_MODULE,
366 .name = "fusectl",
367 .init_fs_context = fuse_ctl_init_fs_context,
368 .kill_sb = fuse_ctl_kill_sb,
369};
370MODULE_ALIAS_FS("fusectl");
371
372int __init fuse_ctl_init(void)
373{
374 return register_filesystem(&fuse_ctl_fs_type);
375}
376
377void __exit fuse_ctl_cleanup(void)
378{
379 unregister_filesystem(&fuse_ctl_fs_type);
380}
381

source code of linux/fs/fuse/control.c