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(file)->i_private;
28	if (fc)
29		fc = fuse_conn_get(fc);
30	mutex_unlock(&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(&fc->num_waiting);
60		file->private_data = (void *)value;
61		fuse_conn_put(fc);
62	}
63	size = sprintf(tmp, "%ld\n", (long)file->private_data);
64	return simple_read_from_buffer(buf, len, ppos, tmp, 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(tmp, "%u\n", val);
72
73	return simple_read_from_buffer(buf, len, ppos, tmp, 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(buf, count, 0, &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,
127				    max_user_bgreq);
128	if (ret > 0) {
129		struct fuse_conn *fc = fuse_ctl_file_conn_get(file);
130		if (fc) {
131			spin_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(&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,
170				    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(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(d_inode(parent));
262	sprintf(name, "%u", fc->dev);
263	parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, 2,
264				     &simple_dir_inode_operations,
265				     &simple_dir_operations);
266	if (!parent)
267		goto err;
268
269	if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400, 1,
270				 NULL, &fuse_ctl_waiting_ops) ||
271	    !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200, 1,
272				 NULL, &fuse_ctl_abort_ops) ||
273	    !fuse_ctl_add_dentry(parent, fc, "max_background", S_IFREG | 0600,
274				 1, NULL, &fuse_conn_max_background_ops) ||
275	    !fuse_ctl_add_dentry(parent, fc, "congestion_threshold",
276				 S_IFREG | 0600, 1, NULL,
277				 &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(d_inode(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(&fuse_mutex);
328			return err;
329		}
330	}
331	mutex_unlock(&fuse_mutex);
332
333	return 0;
334}
335
336static int fuse_ctl_get_tree(struct fs_context *fsc)
337{
338	return get_tree_single(fsc, 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(&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