control.c

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