fs/fuse/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
  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  */
  21 static struct super_block *fuse_control_sb;
  22
  23 static 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
  34 static 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
  47 static 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
  67 static 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
  76 static 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
 102 static 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
 119 static 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
 144 static 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
 161 static 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);
 179 out:
 180         return ret;
 181 }
 182
 183 static const struct file_operations fuse_ctl_abort_ops = {
 184         .open = nonseekable_open,
 185         .write = fuse_conn_abort_write,
 186 };
 187
 188 static const struct file_operations fuse_ctl_waiting_ops = {
 189         .open = nonseekable_open,
 190         .read = fuse_conn_waiting_read,
 191 };
 192
 193 static const struct file_operations fuse_conn_max_background_ops = {
 194         .open = nonseekable_open,
 195         .read = fuse_conn_max_background_read,
 196         .write = fuse_conn_max_background_write,
 197 };
 198
 199 static const struct file_operations fuse_conn_congestion_threshold_ops = {
 200         .open = nonseekable_open,
 201         .read = fuse_conn_congestion_threshold_read,
 202         .write = fuse_conn_congestion_threshold_write,
 203 };
 204
 205 static struct dentry *fuse_ctl_add_dentry(struct dentry *parent,
 206                                           struct fuse_conn *fc,
 207                                           const char *name,
 208                                           int mode, int nlink,
 209                                           const struct inode_operations *iop,
 210                                           const struct file_operations *fop)
 211 {
 212         struct dentry *dentry;
 213         struct inode *inode;
 214
 215         BUG_ON(fc->ctl_ndents >= FUSE_CTL_NUM_DENTRIES);
 216         dentry = d_alloc_name(parent, name);
 217         if (!dentry)
 218                 return NULL;
 219
 220         inode = new_inode(fuse_control_sb);
 221         if (!inode) {
 222                 dput(dentry);
 223                 return NULL;
 224         }
 225
 226         inode->i_ino = get_next_ino();
 227         inode->i_mode = mode;
 228         inode->i_uid = fc->user_id;
 229         inode->i_gid = fc->group_id;
 230         simple_inode_init_ts(inode);
 231         /* setting ->i_op to NULL is not allowed */
 232         if (iop)
 233                 inode->i_op = iop;
 234         inode->i_fop = fop;
 235         set_nlink(inode, nlink);
 236         inode->i_private = fc;
 237         d_add(dentry, inode);
 238
 239         fc->ctl_dentry[fc->ctl_ndents++] = dentry;
 240
 241         return dentry;
 242 }
 243
 244 /*
 245  * Add a connection to the control filesystem (if it exists).  Caller
 246  * must hold fuse_mutex
 247  */
 248 int fuse_ctl_add_conn(struct fuse_conn *fc)
 249 {
 250         struct dentry *parent;
 251         char name[32];
 252
 253         if (!fuse_control_sb || fc->no_control)
 254                 return 0;
 255
 256         parent = fuse_control_sb->s_root;
 257         inc_nlink(d_inode(parent));
 258         sprintf(name, "%u", fc->dev);
 259         parent = fuse_ctl_add_dentry(parent, fc, name, S_IFDIR | 0500, 2,
 260                                      &simple_dir_inode_operations,
 261                                      &simple_dir_operations);
 262         if (!parent)
 263                 goto err;
 264
 265         if (!fuse_ctl_add_dentry(parent, fc, "waiting", S_IFREG | 0400, 1,
 266                                  NULL, &fuse_ctl_waiting_ops) ||
 267             !fuse_ctl_add_dentry(parent, fc, "abort", S_IFREG | 0200, 1,
 268                                  NULL, &fuse_ctl_abort_ops) ||
 269             !fuse_ctl_add_dentry(parent, fc, "max_background", S_IFREG | 0600,
 270                                  1, NULL, &fuse_conn_max_background_ops) ||
 271             !fuse_ctl_add_dentry(parent, fc, "congestion_threshold",
 272                                  S_IFREG | 0600, 1, NULL,
 273                                  &fuse_conn_congestion_threshold_ops))
 274                 goto err;
 275
 276         return 0;
 277
 278  err:
 279         fuse_ctl_remove_conn(fc);
 280         return -ENOMEM;
 281 }
 282
 283 /*
 284  * Remove a connection from the control filesystem (if it exists).
 285  * Caller must hold fuse_mutex
 286  */
 287 void fuse_ctl_remove_conn(struct fuse_conn *fc)
 288 {
 289         int i;
 290
 291         if (!fuse_control_sb || fc->no_control)
 292                 return;
 293
 294         for (i = fc->ctl_ndents - 1; i >= 0; i--) {
 295                 struct dentry *dentry = fc->ctl_dentry[i];
 296                 d_inode(dentry)->i_private = NULL;
 297                 if (!i) {
 298                         /* Get rid of submounts: */
 299                         d_invalidate(dentry);
 300                 }
 301                 dput(dentry);
 302         }
 303         drop_nlink(d_inode(fuse_control_sb->s_root));
 304 }
 305
 306 static int fuse_ctl_fill_super(struct super_block *sb, struct fs_context *fsc)
 307 {
 308         static const struct tree_descr empty_descr = {""};
 309         struct fuse_conn *fc;
 310         int err;
 311
 312         err = simple_fill_super(sb, FUSE_CTL_SUPER_MAGIC, &empty_descr);
 313         if (err)
 314                 return err;
 315
 316         mutex_lock(&fuse_mutex);
 317         BUG_ON(fuse_control_sb);
 318         fuse_control_sb = sb;
 319         list_for_each_entry(fc, &fuse_conn_list, entry) {
 320                 err = fuse_ctl_add_conn(fc);
 321                 if (err) {
 322                         fuse_control_sb = NULL;
 323                         mutex_unlock(&fuse_mutex);
 324                         return err;
 325                 }
 326         }
 327         mutex_unlock(&fuse_mutex);
 328
 329         return 0;
 330 }
 331
 332 static int fuse_ctl_get_tree(struct fs_context *fsc)
 333 {
 334         return get_tree_single(fsc, fuse_ctl_fill_super);
 335 }
 336
 337 static const struct fs_context_operations fuse_ctl_context_ops = {
 338         .get_tree       = fuse_ctl_get_tree,
 339 };
 340
 341 static int fuse_ctl_init_fs_context(struct fs_context *fsc)
 342 {
 343         fsc->ops = &fuse_ctl_context_ops;
 344         return 0;
 345 }
 346
 347 static void fuse_ctl_kill_sb(struct super_block *sb)
 348 {
 349         struct fuse_conn *fc;
 350
 351         mutex_lock(&fuse_mutex);
 352         fuse_control_sb = NULL;
 353         list_for_each_entry(fc, &fuse_conn_list, entry)
 354                 fc->ctl_ndents = 0;
 355         mutex_unlock(&fuse_mutex);
 356
 357         kill_litter_super(sb);
 358 }
 359
 360 static struct file_system_type fuse_ctl_fs_type = {
 361         .owner          = THIS_MODULE,
 362         .name           = "fusectl",
 363         .init_fs_context = fuse_ctl_init_fs_context,
 364         .kill_sb        = fuse_ctl_kill_sb,
 365 };
 366 MODULE_ALIAS_FS("fusectl");
 367
 368 int __init fuse_ctl_init(void)
 369 {
 370         return register_filesystem(&fuse_ctl_fs_type);
 371 }
 372
 373 void __exit fuse_ctl_cleanup(void)
 374 {
 375         unregister_filesystem(&fuse_ctl_fs_type);
 376 }